![Buchner Pressure Formula
h
dt
dw
g
w
dt
dh
P *
cos
(
*
* +
+
= θ
ρ
ρ
[ ] [ ]
imaginar
al
aginary
al
imaginary
al
imag
al
ih
h
dt
dw
i
dt
dw
g
iw
w
dt
dh
i
dt
dh
P +
+
+
+
+
+
= Re
Im
Re
Re
Re
*
cos
*
*
*
* θ
ρ
ρ
Freeboard
h −
−
= 3
ε
ς
Freeboard
x
kx
h
Freeboard
x
kx
h
−
−
−
=
−
−
−
=
5
5
3
3
5
5
3
3
sin
sin
sin
Im
cos
Re
cos
Re
cos
Re
Re
θ
ε
θ
ε
ς
θ
ε
θ
ε
ς](https://image.slidesharecdn.com/2353978-250528071528-356ae398/85/Design-And-Operation-For-Abnormal-Conditions-Iii-39-320.jpg)
![Buchner Pressure Formula
h
dt
dw
g
w
dt
dh
P *
cos
(
*
* +
+
= θ
ρ
ρ
[ ] [ ]
imaginar
al
aginary
al
imaginary
al
imag
al
ih
h
dt
dw
i
dt
dw
g
iw
w
dt
dh
i
dt
dh
P +
+
+
+
+
+
= Re
Im
Re
Re
Re
*
cos
*
*
*
* θ
ρ
ρ
5
5
5
5
3
3
5
5
5
5
3
3
3
cos
cos
cos
cos
sin
Im
Im
sin
sin
sin
sin
Re
Re
θ
ε
ς
θ
ε
θ
ε
ς
θ
ε
ς
θ
ε
θ
ε
ε
ς
weU
kx
we
x
we
we
kx
we
dt
dh
weU
kx
we
x
we
we
dt
dh
dt
d
dt
d
dt
dh
+
+
+
−
=
+
+
+
=
−
=](https://image.slidesharecdn.com/2353978-250528071528-356ae398/85/Design-And-Operation-For-Abnormal-Conditions-Iii-40-320.jpg)
![Buchner Pressure Formula
h
dt
dw
g
w
dt
dh
P *
cos
(
*
* +
+
= θ
ρ
ρ
[ ] [ ]
imaginar
al
aginary
al
imaginary
al
imag
al
ih
h
dt
dw
i
dt
dw
g
iw
w
dt
dh
i
dt
dh
P +
+
+
+
+
+
= Re
Im
Re
Re
Re
*
cos
*
*
*
* θ
ρ
ρ
5
5
5
5
3
3
5
5
5
5
3
3
5
5
3
cos
cos
cos
cos
Im
sin
sin
sin
sin
Re
*
θ
ε
ς
θ
ε
θ
ε
θ
ε
ς
θ
ε
θ
ε
ς
ε
ε
ε
weu
kx
we
x
we
we
w
weU
kx
we
x
we
we
w
U
dt
d
x
dt
d
w
+
+
+
−
=
+
+
+
−
=
−
−
−
=](https://image.slidesharecdn.com/2353978-250528071528-356ae398/85/Design-And-Operation-For-Abnormal-Conditions-Iii-41-320.jpg)
![Buchner Pressure Formula
h
dt
dw
g
w
dt
dh
P *
cos
(
*
* +
+
= θ
ρ
ρ
[ ] [ ]
imaginar
al
aginary
al
imaginary
al
imag
al
ih
h
dt
dw
i
dt
dw
g
iw
w
dt
dh
i
dt
dh
P +
+
+
+
+
+
= Re
Im
Re
Re
Re
*
cos
*
*
*
* θ
ρ
ρ
kx
we
x
we
we
dt
dw
U
we
kx
we
x
we
we
dt
dw
dt
d
dt
d
dt
du
dt
d
x
dt
d
dt
dw
sin
sin
sin
Im
cos
cos
cos
cos
Re
*
2
5
5
2
3
3
2
5
5
2
2
5
5
2
3
3
2
5
5
2
3
2
ς
θ
ε
θ
ε
θ
ε
ς
θ
ε
θ
ε
ς
ε
ε
ε
−
−
=
+
+
+
−
=
−
−
−
=](https://image.slidesharecdn.com/2353978-250528071528-356ae398/85/Design-And-Operation-For-Abnormal-Conditions-Iii-42-320.jpg)
![thin, careful strokes until they do fit, for the joint will not be good
unless the edges coincide. Remember, however, that it takes more
than merely touching to make a good joint. The surfaces of the
boards must be in line (in the same plane). Of course this really
depends upon the edges being square. Test by holding a straight-
edge, the square, the edge of the plane, or anything straight,
against the surface of the boards (Fig. 553).[47]
Do not be misled by the directions you may see in "amateur"
books and magazine articles which tell you, for cases like this,—
when you wish to glue up the lid of a desk, for instance,—to plane
and sandpaper your boards carefully on the sides and then fit the
edges together, after which you "have only to glue the edges and
the job is done." That is not the right way to make a glued joint, as
you will find out for yourself after you have planed a few dozen
boards the second time. The skilled workman seldom attempts to do
this except in repairing or some case where the surface of the pieces
must be preserved. The practical work-man's way (which is the way
for you), is to glue first and plane afterwards. The best way,
practically, is to glue up the rough boards before they have been
planed at all, and then have the whole planed down as one piece by
machine to the required thickness. Of course you should get the
surfaces as nearly in line as you can, to avoid needless planing
afterwards, but give your special attention to making the joint hold
(see note under Clamps).
Sometimes the edges of boards to be glued are purposely planed,
hollowing lengthways, so that the two pieces touch at the ends, but
do not quite come together in the middle, the idea being that a
clamp at the middle will force the joint together for its whole length
and will give a stronger result than to attempt to make both edges
exactly straight. If there is to be any open place in the joint before
gluing, it is better to have it at the middle than at the ends, but
there is a difference of opinion as to whether there is any advantage
in springing boards to fit in this way.](https://image.slidesharecdn.com/2353978-250528071528-356ae398/85/Design-And-Operation-For-Abnormal-Conditions-Iii-59-320.jpg)
Design And Operation For Abnormal Conditions Iii
- 1. Design And Operation For Abnormal Conditions Iii download https://ebookbell.com/product/design-and-operation-for-abnormal- conditions-iii-4707956 Explore and download more ebooks at ebookbell.com
- 2. Here are some recommended products that we believe you will be interested in. You can click the link to download. Doubleshift Schooling Design And Operation For Costeffectiveness Third Edition Mark Bray https://ebookbell.com/product/doubleshift-schooling-design-and- operation-for-costeffectiveness-third-edition-mark-bray-2029972 A Holistic Approach To Ship Design Volume 1 Optimisation Of Ship Design And Operation For Life Cycle 1st Ed Apostolos Papanikolaou https://ebookbell.com/product/a-holistic-approach-to-ship-design- volume-1-optimisation-of-ship-design-and-operation-for-life-cycle-1st- ed-apostolos-papanikolaou-7321048 Design And Operation Of Production Networks For Mass Personalization In The Era Of Cloud Technology 1st Edition Dimitris Mourtzis https://ebookbell.com/product/design-and-operation-of-production- networks-for-mass-personalization-in-the-era-of-cloud-technology-1st- edition-dimitris-mourtzis-36427248 Safe Design And Operation Of Process Vents And Emission Control Systems Ccps Concept Books Center For Chemical Process Safety Ccps https://ebookbell.com/product/safe-design-and-operation-of-process- vents-and-emission-control-systems-ccps-concept-books-center-for- chemical-process-safety-ccps-2614826
- 3. Building Performance Simulation For Design And Operation Jan Lm Henseneditor Roberto Lambertseditor https://ebookbell.com/product/building-performance-simulation-for- design-and-operation-jan-lm-henseneditor-roberto- lambertseditor-10413682 Building Performance Simulation For Design And Operation 2nd Edition Jan L M Hensen Roberto Lamberts https://ebookbell.com/product/building-performance-simulation-for- design-and-operation-2nd-edition-jan-l-m-hensen-roberto- lamberts-11819488 Sustainable Practices For Landfill Design And Operation 1st Edition Timothy G Townsend https://ebookbell.com/product/sustainable-practices-for-landfill- design-and-operation-1st-edition-timothy-g-townsend-5353258 Standard Practice For The Design And Operation Of Supercooled Fog Dispersal Projects Asce Standard Ansiasceewri 4413 2nd American Society Of Civil Engineers https://ebookbell.com/product/standard-practice-for-the-design-and- operation-of-supercooled-fog-dispersal-projects-asce-standard- ansiasceewri-4413-2nd-american-society-of-civil-engineers-5394622 Standard Practice For The Design And Operation Of Precipitation Enhancement Projects Not Available https://ebookbell.com/product/standard-practice-for-the-design-and- operation-of-precipitation-enhancement-projects-not-available-5427196
- 5. RINA INTERNATIONAL CONFERENCE DESIGN AND OPERATION FOR ABNORMAL CONDITIONS III 26 – 27 January 2005 © 2005: The Royal Institution of Naval Architects The Institution is not, as a body, responsible for the opinions expressed by the individual authors or speakers THE ROYAL INSTITUTION OF NAVAL ARCHITECTS 10 Upper Belgrave Street London SW1X 8BQ Telephone: 020 7235 4622 Fax: 020 7259 5912 ISBN No: 1-905040-08-3
- 6. Investigation into the influence of Forecastles, Bow Visors and Pitched Hatch Covers on Green Water Loads Benedict Graat
- 7. Investigation into the influence of forecastles, bow visors and pitched hatch covers on green water loads Investigate the influence of pitched hatch covers, forecastles and bow visors on green water loads Validate Hoi Sang Chaungs 2D Motion Program Investigate the use of Buchner Pressure Formula and Spectrum Analysis techniques as a design stage method to predict green water loadings
- 8. Investigation into the influence of Forecastles, Bow Visors and Pitched Hatch Covers on Green Water Loads MV Derbyshire Green seas Behaviour of green water Conditions giving rise to green water loading Design features to defend against green seas Analytical Investigation Design stage method to predict loadings Model Tests Empirical Relationships Conclusions
- 10. Supporting Evidence from the Wreckage
- 11. Supporting Evidence from the Wreckage
- 12. Green Seas Vertical motion relative to the local wave elevation exceeds the local freeboard
- 13. Behaviour of Green Water Relative wave motions around the bow Sequence of Events Water flows onto the deck Shallow water wave over the deck Final impact of water to the structure
- 14. Bow goes down into a wave and creates a vertical wall of water around the bulwark
- 15. Jet hits forward deck equipment and stops suddenly on hatch coaming
- 16. Water deflected above the hatch falls on aft part of No.1 hatch
- 17. Conditions giving rise to green water loading When the length of a ship is very close to the dominant wavelength, a vessel will become subject to very large pitch and relative vertical motions
- 18. Seakeeping Studies Ships with shorter ship lengths to wavelengths can: • Contour the waves to a greater extent • Weather a storm better In irregular seas: Pitch motion reduces with increase in length L 1 Pitch Motion a L L L = Motions at extreme ends likely to increase
- 19. Design features adopted to defend against green seas Forecastle Shear
- 20. Design Features adopted to defend against Green Seas
- 21. Design Features adopted to defend against green seas Increase freeboard at the fore-end
- 22. Proposed Design Features to defend against green seas
- 23. Proposed Design Features to defend against Green Seas
- 24. Analytical Design Stage Method Use 2D Motion Program to Calculate Motion RAOs at various wave frequencies Input Motion RAOs into Buchner Pressure Formula to calculate a Pressure RAO for each frequency Apply Spectrum Analysis to calculate extreme, significant pressures and probablities of exceedance Investigate Empirical Relationships
- 25. Experimental Method Apply FFT Analysis to experimental data to obtain Motion RAOs for each wave frequency Input Motion RAOs into Buchner Pressure Formula to calculate a Pressure RAO for each frequency Apply Spectrum Analysis to calculate extreme, significant pressures and probablities of exceedance Investigate Empirical Relationships
- 26. Motions and Relative Motions Relative Motions around the bow – input to green water problem R = ζ – z H = r- fb εr = ε3 + yε4 -xε5 − ζ
- 27. Motion Program
- 28. Motion Program
- 29. Heave Response Amplitude Operators Heave RAOs 0 0.1 0.2 0.3 0.4 0.5 0.00 0.50 1.00 1.50 Wave Frequency Heave RAO Heave RAO 7m Heave RAO 14m Motion Amplitudes
- 30. Heave Phase Angles Heave Phase Angles -4 -3 -2 -1 0 1 2 3 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 Wave Frequency H e a v e P h a se A n g le Heave Phase Angle Heave Phase Angle Phase Angles
- 31. Pitch Response Amplitude Operators Pitch Motion RAOs 0 0.002 0.004 0.006 0.008 0.01 0.00 0.50 1.00 1.50 Wave Frequency Pitch RAO Pitch RAO 7m Pitch RAO 14m Motion Amplitudes
- 32. Pitch Phase Angles Pitch Phase Angles -3 -2 -1 0 1 2 3 4 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 Wave Frequency P itc h P h a s e An g le Pitch Phase Angle Pitch Phase Angle Phase Angles
- 33. Motion Program RAO Motion ProgramRAO 0 0.5 1 1.5 2 2.5 0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400 1.600 WaveFrequency Relative Motion RA O
- 34. Relative Motion RAO Relative Motion RAO 0 0.5 1 1.5 2 2.5 0.000 0.500 1.000 1.500 Wave Frequency Re la tive M otion RAO Motion Program Relative Motion RAO 14m Wave Test RAO 14m Wave Test RAO 14m Wave Test RAO 7m Wave Test RAO
- 35. Pressure on the deck resulting from green seas Breaking or plunging waves impacting on the deck can generate very steep pressure impulses
- 36. Analytical Investigation Assumed that pressure of water at the deck is equal to: Static water pressure Static water pressure corrected for the vertical acceleration of the deck Impulsive pressure of a falling breaking wave Impulsive loading is due to the rate of change of water height on the deck
- 38. Buchner Pressure Formula m dt dw w dt dm dt w m d F + = = ) . ( h dt dw g w dt dh P ) cos ( + + = θ ρ ρ
- 39. Buchner Pressure Formula h dt dw g w dt dh P * cos ( * * + + = θ ρ ρ [ ] [ ] imaginar al aginary al imaginary al imag al ih h dt dw i dt dw g iw w dt dh i dt dh P + + + + + + = Re Im Re Re Re * cos * * * * θ ρ ρ Freeboard h − − = 3 ε ς Freeboard x kx h Freeboard x kx h − − − = − − − = 5 5 3 3 5 5 3 3 sin sin sin Im cos Re cos Re cos Re Re θ ε θ ε ς θ ε θ ε ς
- 40. Buchner Pressure Formula h dt dw g w dt dh P * cos ( * * + + = θ ρ ρ [ ] [ ] imaginar al aginary al imaginary al imag al ih h dt dw i dt dw g iw w dt dh i dt dh P + + + + + + = Re Im Re Re Re * cos * * * * θ ρ ρ 5 5 5 5 3 3 5 5 5 5 3 3 3 cos cos cos cos sin Im Im sin sin sin sin Re Re θ ε ς θ ε θ ε ς θ ε ς θ ε θ ε ε ς weU kx we x we we kx we dt dh weU kx we x we we dt dh dt d dt d dt dh + + + − = + + + = − =
- 41. Buchner Pressure Formula h dt dw g w dt dh P * cos ( * * + + = θ ρ ρ [ ] [ ] imaginar al aginary al imaginary al imag al ih h dt dw i dt dw g iw w dt dh i dt dh P + + + + + + = Re Im Re Re Re * cos * * * * θ ρ ρ 5 5 5 5 3 3 5 5 5 5 3 3 5 5 3 cos cos cos cos Im sin sin sin sin Re * θ ε ς θ ε θ ε θ ε ς θ ε θ ε ς ε ε ε weu kx we x we we w weU kx we x we we w U dt d x dt d w + + + − = + + + − = − − − =
- 42. Buchner Pressure Formula h dt dw g w dt dh P * cos ( * * + + = θ ρ ρ [ ] [ ] imaginar al aginary al imaginary al imag al ih h dt dw i dt dw g iw w dt dh i dt dh P + + + + + + = Re Im Re Re Re * cos * * * * θ ρ ρ kx we x we we dt dw U we kx we x we we dt dw dt d dt d dt du dt d x dt d dt dw sin sin sin Im cos cos cos cos Re * 2 5 5 2 3 3 2 5 5 2 2 5 5 2 3 3 2 5 5 2 3 2 ς θ ε θ ε θ ε ς θ ε θ ε ς ε ε ε − − = + + + − = − − − =
- 43. Spectrum Analysis − = 4 2 4 4 2 5 2 3 / 1 496 exp 124 ) ( T w T w H w S Hs Tp Spectrum 1 15m 16.95 Spectrum 2 13.18m 13.9s Spectrum 3 8.5m 7.5s
- 44. Motion Program Pressure Analysis FP Deck Pressure-Forecastle Condition Freq Range 0.2-1.4 rad/s Model Test Frequency Spectrum 1 Spectrum 2 Spectrum 1 Spectrum 2 Hs 15m 13.18m 15m 13.18m Tp 16.95s 13.9s 16.95s 13.9s T 3 3 3 3 n* 0.07 0.08 0.13 0.14 N 804.34 811.03 1,380.86 1528.46 x* (Kpa) 530.6 528.64 65.1 176.59 x 1/3 (Kpa) 291.05 289.88 34.24 92.37 Experimental Data Analysis Spectrum 1 Spectrum 2 Spectrum 3 Hs 15m Hs 13.18m Hs 8.5m Tp 16.95s Tp 13.9s Tp 7.5s T 3 T 3 T 3 n* 0.11 n* 0.11 n* 0.11 N 1137.78 N 1138.53 N 1173.99 x* KPa 92.94 x* Kpa 118.36 x* Kpa 164.93 x 1/3 KPa 49.56 x 1/3 Kpa 63.12 x 1/3 Kpa 87.75
- 45. Weibull Probablity Fit WeibullF itforHs15m,Tp16.95s 14mRegularWaveTests 0 0.2 0.4 0.6 0.8 1 1.2 0 20 40 60 80 100 120 Impact Pressure K Pa Probablity of Exceedance
- 46. Motion Program Pressure Analysis 0 Degree Hatch Cover Freq Range 0.2-1.4 rad/s Model Test Frequency Spectrum 1 Spectrum 2 Spectrum 3 Spectrum 1 Spectrum 2 Hs 15m 13.18m 8.5m 15m 13.18m Tp 16.95s 13.9s 7.5s 16.95s 13.9s T 3 3 3 3 3 n* 0.09 0.08 0.07 0.12 0.1 N 946.54 833.26 715.4 1,307.99 1115.83 x* (Kpa) 386.87 312.05 18.11 154.5 145.54 x 1/3 (Kpa) 210.12 170.6 9.99 81.66 77.7 Experimental Analysis for 0 Degree Hatch Cover Hs 15m Hs 13.18 Hs 8.5 Tp 16.95 Tp 13.9s Tp 7.5 T 3 T 3 T 3 n* 0.11 n* 0.11 n* 0.11 N 1148.9 N 1207.85 N 1215.75 x* Kpa 117.18 x* Kpa 125.15 x* Kpa 187.36 x 1/3 Kpa 15.8 x 1/3 Kpa 66.45 x 1/3 Kpa 99.43
- 47. Weibull Fit –Experimental Analysis 0 deg Hatch Cover W eibull Fit H s 15mTp16.95s 0 0.5 1 1.5 0 20 40 60 80 100 120 Impact Pressure (K Pa) Probablity of Exceedance
- 48. Weibull Fit – Motion Program Analysis 0 deg Hatch Cover 0 Hatch Hs 15m, Tp, 16.95s 0 0.2 0.4 0.6 0.8 1 1.2 0 20 40 60 80 100 120 Impact Pressure (KPa) Probablity of Exceedance
- 49. Overall Results of Analytical Investigation ImpactP ressureatF orepeakvsVisorAngle 0 50 100 150 200 0 5 10 15 20 VisorAngleD egrees Impact Pressure (KPa) S pectrum1 S pectrum2 E xperim entS pectrum1 E xperim entS pectrum2 E xperim entS pectrum3
- 50. Overall Results of Analytical Investigation Im p actP ressu reS en so r2v sV iso rA n g le 0 50 100 150 200 0 5 10 15 20 VisorA ngle(degrees) Im p act Pressure ( KPa ) S pectrum1 S pectrum2 E xperim entS pectrum1 E xperim entS pectrum2 E xperim entS pectrum3
- 51. Model Tests Impact Pressure vs Hatch Cover Angle 0 50 100 150 200 0 10 20 30 40 Hatch Cover Angle degrees Im p a c t P r e s s u r e ( K P a ) Spectrum1 Spectrum2 Experiment Spectrum1 Spectrum2 Spectrum3
- 52. Model Tests Wave Height Speed (Knots) Speed Lamda/L Lw Period Frequency 14m 2 0.13m/s 0.5 134 1.08 1.07 14m 2 0.13m/s 1 268 0.77 0.75 7m 2 0.13m/s 0.5 134 0.94 1.07 7m 2 0.13m/s 0.75 201 1.15 0.87 7m 2 0.13m/s 1 268 1.33 0.75 7m 2 0.13m/s 1.25 334 1.48 0.67 7m 2 0.13m/s 1.5 401 1.62 0.62 7m 2 0.13m/s 1.75 468 1.75 0.57
- 53. Model Tests
- 54. Model Tests
- 55. Another Random Document on Scribd Without Any Related Topics
- 56. Fig. 549. Plaster of Paris (calcined plaster), mixed with very thin hot glue, is excellent for stopping cracks and holes of considerable size. It can be mixed with water only, but this is not as good. Fitting in a plug of wood is a good way when the hole is of such shape that you can do so, making the grain of the plug run the same way as that of the piece to be plugged. Taper the plug slightly, so that when driven in it will fit tightly and not be flush with the surface, but project above it (Fig. 549). Dip in hot glue, and drive well in. When dry smooth off. If the hole is irregular, trim to some shape to which you can fit a plug. In nice work take pains to have the plug a good match for the rest of the wood. Slight cracks at the end of a piece can often be plugged and at the same time secured against further splitting by sawing directly down the crack, so as to remove it and substitute a straight saw-kerf. In this kerf a slip of wood can be fitted and glued. Wax, and also melted shellac, can be used to stop holes and cracks in finished work. For this, see under Finishing. Jack-Plane.—See Plane. Jointer.—See Plane. Jointing.—This term is applied to the act of straightening and making true the edges of two boards or planks which are to be joined to make a tight joint, with glue or otherwise. It is, also, popularly applied to straightening the edge of one piece only, as to "joint" the edge of a board. This you will often have to do, and for jointing two edges which are to be glued particular care will be required. Assuming that the edges have been got out nearly straight, the only plane you will require is the fore-plane,—or better, the jointer, or even the "long" jointer if the piece is long and you are fortunate enough to have these tools,—and it should be set fine, although if the edge is very crooked and you have to work off much
- 57. Fig. 550. Fig. 551. Fig. 552. superfluous stock, the iron can be set to make a coarse shaving at first. In shooting or jointing edges it is customary to hold the finger under the sole of the plane as a guide (Fig. 550). This helps in regard to the common fault of tipping the plane sideways so as to plane off more on one side than on the other (Fig. 551). This trouble may be aggravated by a wrong position of the left hand on the fore part of the plane in case you use a wooden plane (see Fig. 624 for correct position). Keep testing across the edge with the square (Fig. 640). The shooting-board can be used to advantage for short pieces (see Shooting-board), and attachable guides can also be obtained. The jointing should be done with long, deliberate, steady strokes. Any hasty, hit-or-miss slashing away with the plane will be sure to result in a bad joint, and you can easily get the edge into such shape by three or four careless strokes that it will take you a good while to get it straight. Try also to avoid planing the edge rounding, from end to end (see Plane, Figs. 635- 637). Sight along the edge. Also test with straight- edge, looking toward the light. If any shines through, the edge is not yet accurate and the process must be resumed. If you are jointing two edges, as for a "glue-joint," first examine the pieces to see which edges will best go together, according to the purpose for which they are intended. Look at the end grain so as to arrange it in different ways if you are building up a piece of selected parts (Fig. 559). If merely joining two or
- 58. more boards to make a wider one, notice the way the grain runs lengthways, and the way it crops up to the surface, for you will have, for everything but the roughest work, to plane the surface over after the joint is glued, and if the grain runs in two or three different ways it will be harder to make the surface smooth. There are cases, however, in handsomely figured wood, as quartered oak or mahogany, where you will arrange the grain in the way that will look the best, but in such cases you expect to go through extra labour for the sake of having the article as handsome as possible. With soft, straight-grained white pine or whitewood, these matters are of less importance. When you have the pieces laid together in the best way, mark on the surface right across the joints (Fig. 552) so that you will know how to put the pieces together, for you will forget how they were arranged after you have moved them around a few times. Fig. 553. Joint each edge separately. For nice work it is well to joint the edges of the successive pieces alternately from opposite sides,—that is, if in planing the edge of the first piece the marked (or face) side of the board is towards you, plane the edge of the next piece with the face side of the board against the bench, or away from you. This helps to counteract the result of any tendency to tip the plane to one side or any inaccuracy in setting the plane-iron. See Shooting-board. Then, putting one piece in the vice with the jointed edge upwards, lay the other edge upon it in the proper position and see if the two edges touch throughout. If not, one or both must be planed with
- 59. thin, careful strokes until they do fit, for the joint will not be good unless the edges coincide. Remember, however, that it takes more than merely touching to make a good joint. The surfaces of the boards must be in line (in the same plane). Of course this really depends upon the edges being square. Test by holding a straight- edge, the square, the edge of the plane, or anything straight, against the surface of the boards (Fig. 553).[47] Do not be misled by the directions you may see in "amateur" books and magazine articles which tell you, for cases like this,— when you wish to glue up the lid of a desk, for instance,—to plane and sandpaper your boards carefully on the sides and then fit the edges together, after which you "have only to glue the edges and the job is done." That is not the right way to make a glued joint, as you will find out for yourself after you have planed a few dozen boards the second time. The skilled workman seldom attempts to do this except in repairing or some case where the surface of the pieces must be preserved. The practical work-man's way (which is the way for you), is to glue first and plane afterwards. The best way, practically, is to glue up the rough boards before they have been planed at all, and then have the whole planed down as one piece by machine to the required thickness. Of course you should get the surfaces as nearly in line as you can, to avoid needless planing afterwards, but give your special attention to making the joint hold (see note under Clamps). Sometimes the edges of boards to be glued are purposely planed, hollowing lengthways, so that the two pieces touch at the ends, but do not quite come together in the middle, the idea being that a clamp at the middle will force the joint together for its whole length and will give a stronger result than to attempt to make both edges exactly straight. If there is to be any open place in the joint before gluing, it is better to have it at the middle than at the ends, but there is a difference of opinion as to whether there is any advantage in springing boards to fit in this way.
- 60. Fig. 554. Fig. 555. Fig. 556. Fig. 557. Before gluing hardwood edges, it is well to tooth them over with the toothed-plane, if you have one. (See Plane.) See Plane, Gluing, Joints, Cleating, Dowelling, etc. Joints and Splices.—There are many kinds of splices and joints used in the different branches of wood-work, a few of which are here given. The common square butt-joint (Fig. 554) is the simplest way to join two pieces at right angles, as in making a box or frame, and is used for all common work. Glue is of but little use with this joint. Rely wholly on nails or screws. To make a better joint, cut a rabbet at the end of one piece and you have a joint (Fig. 555) which shows less end wood, and can be helped a good deal by gluing, on account of the shoulder. Another way is shown in Fig. 556. Some strength and stiffness is gained by the tongue and groove, but a groove near the end introduces an element of weakness. A much stronger way and a tighter joint (Fig. 557) is often used for cisterns, water-tanks, and horse troughs, but the projecting ends are objectionable for most purposes. See Halving, Mitring, Dovetailing, and also Box-making, page 219. In nailing any such joints as those just shown, remember to always bore holes for the nails wherever there is danger of splitting. See Awl, Bits, Boring, Nailing. There are many ways, besides those just mentioned, for joining sticks and timbers at right angles, which is something you will often have to do, whether for a kite or some small framework or for the timbers of a building.
- 61. Fig. 558. To join two or more boards or planks to make a wider surface, several methods can be used. Cleating, though strong and suitable for all such work as drawing- boards, rough doors, and the like, is often undesirable, both on account of the looks and because the cleats may be in the way (see Cleating). The simplest way, without cleats, is to glue the jointed edges (see Jointing and Gluing). Dowels can be used with this joint (see Dowelling), or grooves can be cut and a strip or spline or tongue inserted (Fig. 558). This last way can be done at the mill quicker and better than by hand. The edges can also be halved, or a rabbet cut in each edge from opposite sides. The boards can also be "matched" (see page 46), in which case it is not usual to glue them. All of these joints can best be made by machine. Fig. 559. To avoid the warping and change of shape to which wide pieces are subject, particularly when they are not middle boards (see Chapter III), they are often built up of selected narrower pieces (Fig. 559). This is done for many things,—the frames of machines, the tops of sewing-tables, drawing-boards, chopping-blocks, etc. Masts, bows, fishing-rods, and the like are sometimes built up of selected pieces, the idea being that a better result can be obtained by combining selected smaller pieces, that flaws and defects (which are apt to occur in larger pieces) can be avoided, and that sometimes the grain can be arranged to better advantage. This is doubtless true, but there is always the objection that glued joints may give way. If you can get a piece which is practically perfect, it is probably in most cases better than a glued-up combination, for it is not easy to improve on Nature when you can get her best specimens; but
- 62. Fig. 560. Fig. 561. unless you can get first-class stock of the dimensions required, it is better to "build up" with smaller pieces of selected stock. Where the ends of two pieces come together and you wish to make a close joint, you will, of course, saw the pieces off as squarely as possible, using the square or perhaps the mitre-box. If you mark and saw them with exactness, and if everything about their arrangement is straight and square and true, the ends will come together exactly and make a close joint, but as a practical matter this frequently will not happen, however careful you may be. For nice work, the workmanlike way in such cases is to plane or pare the ends until they fit, but for rougher work the expedient of sawing the ends to fit can be resorted to. To do this, put the ends together as they are to go (Fig. 560), keep them from moving, and saw straight down through the joint. As the saw will leave a kerf of uniform thickness, the pieces can now be pushed together and the ends will fit, unless the joint was very much open, in which case you have only to saw again, and if necessary repeat the operation until the ends fit. This is a very useful expedient in case of need, but should not be relied on as a regular way to make joints, lest it engender a careless and inaccurate method of work. This applies also to joints which meet at any angle. In some cases, where only one side of each piece shows, as in laying floor-boards, it is usual to undercut the ends slightly—that is, to make the joint a little open at the bottom, which gives a tight and neat joint on the side which shows (Fig. 561, which is exaggerated). Another way to make an end joint is by bevelled scarfing or splaying (Fig. 562). You will see the ends of the clapboards on old houses joined in this way, and it doubtless makes a better joint in many cases than the common square or butt-joint, but it is more work. Strips of moulding are often cut in this way.
- 63. Fig. 562. Fig. 563. Fig. 564. There are many ways of splicing two or more pieces so as to get greater length, many of them, such as are used in bridge-building and roof-framing, being quite complicated. You will rarely, however, in such work as you will do at first, have occasion to do more than nail strips (fish-plates) on the sides of the pieces or make a halved splice or scarfed joint (Fig. 563). The latter is often made longer than that shown and fastened in various ways. A joint for a brace is shown in Fig. 564. See Cleats, Doors, Dovetailing, Dowelling, Gluing, Halving, Mitring, Mortising, Nailing, etc. Keyhole Saw.—See Saw. Knife.—An excellent knife for shop work is a sloyd knife. A good shoe-knife will do very well. This is better for shop work than a jack- knife. It will not close on your fingers for one thing. For general purposes, however, a pocket-knife is the best thing, as you cannot carry a sloyd knife around with you. In buying it get a good plain knife with not more than two or three blades and of the best steel you can afford. Do not waste money in trying to get your whole kit of tools into the compass of one jack-knife handle. In selecting a knife, open the blades and sight along the back to see that each
- 64. blade is accurately in line with the handle, as they are sometimes fastened at a slight angle, which weakens the knife. An immense variety of work can be done with a common pocket- or jack-knife, which is the best emergency tool for either the beginner or the skilled workman. One great thing about whittling is that you cannot rely on squares, rules, or compasses to get your work right, but must be independent, think quickly, look sharply, and rely on your own faculties. A knife is so easy to sharpen that there is not much excuse for using a dull one. See Sharpening. In cutting, always keep your left hand behind the blade, and as a general rule cut from you, for the tool may slip and cut you instead of the wood. There are cases where you have to cut towards you, but there is never any need of getting your left hand in front of the cutting-edge. Level.—A spirit-level is important for some work, but not often necessary for the beginner, as a substitute can easily be made. A horizontal or level line being at right angles with a vertical line, a home-made level can be made by using the principle of the plumb- line, as shown on page 96. When the plumb-line hangs freely on the line ab, which is at right angles to cd, the latter line (cd) must of course be level. The frame should be several feet long for levelling large work, as it can be adjusted more accurately than if small. Linseed Oil.—See Finishing and Painting. Locks.—Use locks of good quality or none at all. Never put very cheap locks on good work. There are many varieties of locks, some to be screwed on the outside of the wood, others to be sunk in recesses cut in the side of the wood, others still to be let into mortises—chest-locks, door-locks, cupboard-locks, drawer-locks, etc. To fit a chest- or box-lock (not a mortise-lock), place the lock in the right position, mark around the part required to be sunk in the wood, which can be cut away with gouge and chisel, the keyhole having been bored quite through the wood and trimmed to a neat
- 65. outline which will conform to the shape of the key. When the lock has been screwed in its recess, put the "hasp," or part which is to be on the lid, into its place in the lock, just where it will be when the chest is locked. Then close the lid, and by slightly pressing you can make a mark on it to show where to put the hasp. Sometimes you can mark the place with a pencil, or by putting transfer-paper between the hasp and the wood, or by rubbing blackened grease on the plate of the hasp. The plate of the hasp should be sunk in the lid to be flush with the surface, and may then be screwed on, bearing in mind the thickness of the lid when selecting the screws. A mortise-lock is fitted in a similar way, but let into a mortise (see Mortising). To fit a common drawer-lock, determine the place for the keyhole and place the lock in position on the inside as before. With a pencil mark the outline of the box-part of the lock, which bears against the wood. Cut away the wood within this line, making a recess slightly deeper than the thickness of the box-part of the lock. The hole must be bored for the key, as before. Put the lock into place and mark the outline of the outer plate, not merely on the inside of the drawer front but also on the top edge. Cut away the wood with the chisel to let the plate sink flush with the wood. When the keyhole is shaped, try the lock and if it works, screw it on. Close the drawer and turn the key hard to raise the bolts (the tops of which have been previously rubbed with blackened grease, such as can be scraped from an oil-stone, or using transfer paper), which, pressing against the wood, will mark the places for the mortises into which they are to slide. Cut these mortises and the drawer can be locked. The variety of locks and their arrangement in regard to fitting is so great that it will be best for you to examine a well-fitted lock for the same purpose that the lock you have to fit is intended, for one rule cannot be given for all cases. Mallet.—The mallet, which is merely a hammer with a wooden head, is made in various forms and sizes, from the big beetle of the
- 66. Fig. 565. wood-chopper to the ladies' carving mallet. It is used to strike the wooden tool-handles. For heavy work a mallet with the handle put through the head from the outside, like the handle of a pickaxe, is good because the head cannot come off. A rounded head with the handle on the end (like a potato-masher) saves having to notice how you hold it, as it is equally effective in any position. A mallet of this type can be turned all in one piece. Hickory or lignum-vitæ or any dense, hard wood is good for a mallet. You do not gain force by using the mallet instead of the hammer, but the softer and more yielding blow of the mallet saves the tool- handle. Marking.—For all rough work the ordinary carpenter's pencil, sharpened flatways, like a screw-driver, is the most convenient and durable instrument. For nicer work, where you need more accurate lines, the common round pencil (medium hard or rather soft) is all you need, but for nice, close work (such as marking accurate joints), a knife, the corner of a chisel, a marking-awl, or a scriber of some sort is necessary. There is no need to buy any tool for this, although they are to be had—nothing is better than a common pocket-knife or a chisel. Keep your pencils sharp by rubbing them on a piece of fine sandpaper, or an old file. In scribing with the chisel, the edge is drawn along with one corner slightly raised and the flat side next the straight-edge, holding the tool either like a pencil or for deeper scoring as in Fig. 565. In all marking and scribing, whether with pencil, awl, knife, chisel, or other tool, be sure that the marking edge is kept close up to the rule, straight-edge, or square, as it will often tend to follow the grain of the
- 67. THIN RULE—FINE WORK. Fig. 566. THICK RULE—ROUGH WORK. Fig. 567. wood and run off the line, and will sometimes force the straight- edge or square out of position if the latter is not held firmly. Do not try to stop lines which meet at a given point, but let them cross one another when they will not show in the finished work, as it is quicker to do so and the crossing of two lines marks a point more accurately than a dot. For work to be finished, however, scoring the surface with lines should be avoided wherever they will show, as they will become conspicuous after the work is finished. In marking lines with a straight-edge or ruler you must be careful that it does not slip. If it is long you can put weights on it. To mark a line accurately through given points, the ruler should not quite touch the points, but be pushed almost up to them and equally distant from each (Fig. 566). This will give you a clear view of both points so that you can be sure that the pencil or whatever you mark with will go as nearly as possible through the centre of each. Bearing the pencil against the edge of the ruler, you can slant it a trifle till the pencil-point will just coincide with the given point on the wood, and, keeping the same inclination, move the pencil along the ruler, and it should also go through the second given point. This applies to a regular ruler with a comparatively thin edge, and to fine work only. In marking by a thick edge, or where extreme nicety is not required, you will of course put the straight- edge right up to the points and run the pencil-point along in the angle (Fig. 567). Besides marking lines, the straight-edge (in some form), is used to determine whether a surface is true. See Straight-edge. For rough, off-hand marking, particularly on undressed stock, chalk is often best. Sticks, shaped like school-crayons, of graphite or
- 68. some black composition, are good for rough marking. The chalk-line is used for distances too great to be covered conveniently by a straight-edge and in places where the latter could not so well be used. The chalk-line is a chalked cord drawn taut between the two points to be connected. It is better to use a small cord than a large one, and blue chalk is often preferred to white. Fasten one end of the cord with a loop around an awl or nail at one end of the desired line, and from this point chalk the cord, holding it between the thumb and the chalk so that the cord will bear on the flat side of the chalk in such a way as to wear it away evenly without cutting it in two. Then draw the chalked cord tight to the other end of the desired line and, holding the end down with one hand, lift the cord from as near the middle as practicable with the thumb and forefinger of the other hand and let it snap back on to the surface. The cord should be raised squarely from the work and not pulled slantingly to one side or the line will not be straight. Marking-Awl.—See Awl. Marking-Gauge.—See Gauge. Matching-Plane.—See Plane. Measurements and Measuring.—For various suggestions, see Rule, and also pages 47, 48, 50, 167 (footnote), 244, and 261. Mirror-Plates.—A good way to fasten such articles as mirrors, cabinets, etc., to the wall is by mirror-plates, which you can buy or make yourself of brass. These should be sunk in the wood so as to be flush with the back side of the shelves. After being fitted, they should be taken off during the process of finishing the work. Mitre.—See Mitring. Mitre-Board.—See Mitring and also page 92. Mitre-Box.—If you can afford it, an iron mitre-box which will cut at various angles will be very useful. You can make one yourself of
- 69. wood. You can get a carpenter to make you one for a small sum, but the iron ones are better. See page 90. Mitre Shooting-Board.—See page 94. Mitring.—A common joint is the mitre (Fig. 568). Its only advantage is that it shows nothing but a line at the angle and the "end wood" is entirely concealed. It is a weak joint at best, even when made by a skilled workman, and is particularly hard for an amateur to make well. The slightest variation in one of the corners of a frame or box throws the whole structure out of shape and in attempting to correct the error the other joints are apt to be opened, and if the whole is finally got together in a fashion it is often after bother enough to have accomplished much good work in some other way.
- 70. Fig. 568. Fig. 569. Fig. 570. The mitre is particularly unscientific for wide pieces used flatways (Fig. 569), as the inevitable expansion and contraction of the pieces is very apt to cause an open joint. If the wood is not quite dry, so that it shrinks, the joint may open permanently toward the inside corner, for when the wood shrinks in width the pieces will become narrower and so separate at the joint, leaving a crack, tapering from the inner to the outer corner. Even if the wood is thoroughly seasoned it will expand and contract more or less. When it expands, the joint will tend to open at the outer corner (Fig. 570). When it contracts it will tend to open, as just shown (Fig. 571), at the inner corner. Fig. 571. Fig. 572. Fig. 573. Of course there are some cases, as in making a picture frame of prepared "mouldings," when mitring is the only way in which the frame can be put together, and there are some other cases in which
- 71. Fig. 574. it is the most proper and suitable joint, but as a general rule, for amateur work, particularly in framing where strength is a consideration, avoid the mitre. Other and better forms for anything like a box are shown in Figs. 554, 555, 556, 557. The mitre is sometimes strengthened for box work and the like by fitting a spline or tongue with the grain running across and not lengthways of the joint (Fig. 572.) This, properly glued under pressure, makes a good joint and one much superior to the plain mitre. But, though easy to do with machinery, it is a slow and careful job to make such a joint by hand, and if a case arises where you wish it done you had best take the work to a factory, where a circular saw is all that is needed. The principle of halving shown in Figs. 539 and 543, can also be applied to a mitred joint. Saw-kerfs are often made (Figs. 573 and 574) into which small strips are tightly fitted and glued. This is a good way and easily done, once having got the mitre properly put together. A combination of the mitre with the joint shown in Fig. 555 is shown in Fig. 575. See also Dovetailing and Joints. Fig. 575.
- 72. Fig. 576. To lay off a mitre, or the lines by which to cut the intersection of any two pieces at any angle, a simple way is that shown in Fig. 576. The pieces are laid one above the other at the desired angle. Then the points of intersection are marked on each edge. Lines connecting these points will give the desired angles for sawing. The square can be used to help in determining the points accurately and to project them to the upper side of the top piece. Mortise and Tenon.—See Mortising. Mortise-Chisel.—See Chisel. Mortise-Gauge.—See Gauge. Mortising (Mortise and Tenon).—If you can get out two pieces and fit them together accurately with a mortise-and-tenon joint, and do the work well, you will be competent to handle a great many of the difficulties of ordinary wood-work. You will often have occasion to use this joint. The mortise is the hole in one of the two pieces to be joined. The tenon is the pin or projection in the other piece, shaped to fit the mortise. To lay out a mortise and tenon (Fig. 577), select and mark the working faces for each piece. First take the piece in which the mortise is to be cut (Fig. 578). Square two lines, ab and cd, across the face and the same distance apart as the width of the piece on which the tenon is to be cut. Carry these lines across the side X (ae and cf) and also across the side opposite to X (that is, the side where the tenon will come through). Next take the tenon-piece (Fig. 579) and measure from the end a distance a little greater than the width of the face of the mortise- piece, and at this point square a line, gh, across the face of the
- 73. Fig. 577. Fig. 578. Fig. 579. Fig. 580. tenon-piece. Continue this line, gi, around the piece, with the square. Now take the gauge and, setting it at the distance from the face settled upon for the mortise, scribe the line jk on the side X and also on the side opposite X. Also from the face of the tenon-piece, without changing the gauge, mark the line lm on the side X, on the opposite side, and on the end. Set the gauge to measure from the face to the other side of the mortise,—that is, add the width of the mortise to the figure at which the gauge was set,—and scribe another set of lines, op and rs, in the same manner as before, remembering to gauge all the time from the same face. In the coarser kinds of work, where marks on the surface do no harm, the gauge marks can be run across the other lines, as being easier and more distinct, but in fine work, especially that which is to be finished, care should be taken not to make scratches that will be seen when the work is finished. The parts to be cut away are indicated by cross marks (Fig. 580) and it will be seen at once that the tenon and mortise are laid out correctly. To cut, take first the mortise-piece and fasten it securely by vise or clamp in a convenient position. The simplest way to remove the wood is to bore a series of holes with a bit of a diameter as nearly the width of the mortise as you have (Fig. 580), but a trifle smaller. This removes a large part of the wood with but slight danger of splitting. The rest can easily be trimmed away to the lines with the
- 74. Fig. 581. Fig. 582. chisel, taking care not to jam the chisel down lengthways of the mortise when the latter is blocked with chips or firm wood, or the wood may split off at the side of the mortise. To cut out the wood with the chisel only (or to trim the ends of the mortise after using the bit), bear in mind the way the chisel acts when you drive it into the wood. If both sides of the chisel were bevelled (as is the case with carving chisels), it would tend to go straight down into the wood, and if held vertically would make a vertical cut (Fig. 581), but the chisels you use for mortising are flat on one side and bevelled on the other. Being one-sided in this way, the edge of the tool is forced by the inclined bevel to slide off, so to speak, more or less, in the direction of the side which is flat. You can prove this easily by holding a chisel across the grain of a board and driving it in. If you hold the tool lightly, you will see that as you drive it in it will incline to cut under, always on the side which is flat (Fig. 581). This shows how to go to work to cut a mortise so as to keep the sides square and true. If you put the chisel at the end, flat side outward, the cut will tend to run under and make the hole too large below the surface. If you turn the tool the other way, it tends to slip in towards the middle of the mortise. So, to cut out the wood, take a chisel just a trifle less in width than the mortise, and, beginning near the middle of the mortise, hold the chisel as in Fig. 582 and make successive cuts, working toward the end, first in one direction and then in the other, giving the chisel handle a slight pull toward the centre of the mortise each time you move it, to loosen the chips (Fig. 583). You can thus work safely toward the ends, which will be left slanting (Fig. 584).
- 75. Fig. 583. Fig. 584. Fig. 585. After cutting about half through the piece in this way, turn it over and repeat the process from the other side, the result being a hole like that shown in Fig. 585. Now turn the chisel around with the flat side toward either end of the hole, and you can pare down the ends to the line without danger of undercutting (Fig. 585). Care must be taken not to jam the chisel down lengthways of the grain until the hole is practically cleared of wood, or the side of the mortise may be split off. Use the chisel lengthways of the grain only at the end of the process, to pare the sides of the mortise evenly, with light strokes, down to the line. In all the use of the chisel, take pains to hold it vertically as regards the sides of the mortise—that is, do not tip it over sideways, or the mortise will be slanting or too wide at the bottom. The common firmer-or paring-chisel can be used for all light mortising, but for heavy work the regular mortising-chisel should be used (see Chisel). To cut the tenon, simply saw carefully on the line gh and its opposite (Fig. 579) and then on the lines lm and rs. Be careful not to cut beyond the line, so as to make the tenon too small. It is easy to trim it a little with the chisel if it is too large. Cut a little bevel around the end of the tenon, so that it will drive through smoothly without
- 76. catching and tearing the sides or ends of the mortise. When it goes through properly and the tenon and shoulder fit snugly, the projecting end of the tenon can be sawed off after the whole job is done. The tenon should be just large enough to drive through with a slight pressure and fit snugly without any wobbling around. It should not be so tight as to require much force to drive it home, or there will be danger of splitting out the sides of the mortise. Fig. 586. Fig. 587. Fig. 588. There is no absolute rule as to how wide to make the mortise and tenon in proportion to the width of the pieces. It depends on the kind of work, the kinds of wood, the kind of strain to be put on the joint, and various circumstances too complex to be gone into here. If the tenon is very thin it will be weaker than the sides of the mortise (Fig. 586). If very thick, the sides of the mortise will be too thin and will be weaker than the tenon (Fig. 587). One third of the width is as thin as a tenon is often made. It will then sometimes be weaker than the sides of the mortise, as you can see from Fig. 588. But it all depends on what the joint is for. If it is to stand violent wrenching, the tenon in this case might break before the mortise-cheeks, and had best be made a little thicker, with the sides of the mortise a little thinner; but, on the other hand, if the joint is merely to hold the tenon-piece in position, as in case of a post resting on a sill, one third is plenty wide enough for the tenon, as it will be best not to weaken the sill by cutting any larger mortise than is necessary. Sometimes the tenon-piece is simply let in to the other piece for its
- 77. Fig. 589. Fig. 590. Fig. 591. Fig. 592. full width. This is called housing (Fig. 589). Two thirds of the width of the piece is thicker than you will be likely to have occasion to make a tenon, as this leaves the cheeks of the mortise very thin. It is wholly a matter of judgment (between, say, one third and two thirds of the width), according to the conditions of each job. The length to which a mortise can safely be cut is also a matter of judgment according to circumstances. If the tenon is thin, the mortise can be longer than if the tenon is thick, as the cheeks will be thicker and stronger, but, as a rule, avoid trying to make very long mortises, unless the tenon is very thin and the wood very strong, as there will not be strength enough left in the cheeks of the mortise (Fig. 590). Six times as long as it is wide is about as long as it is well to make a mortise under ordinary circumstances, though, as just said, it all depends on the conditions of the particular piece of work. When a wide piece is to be mortised into another piece, two or more tenons are sometimes cut, thus avoiding too long a mortise, but this will not do for very wide pieces, unless some of the tenons are fitted loosely, for the expansion and contraction of the wide piece may cause it to buckle or split if all the mortises fit snugly (Fig. 591).
- 78. In such cases as a door-frame or when the end of a board is to be fitted into the side of a post, a tongue and groove is often used in addition to the tenon, and this (known as "relishing") is a good way to do (Fig. 592). Fig. 593. The mortise and tenon given above is a very simple form. Sometimes the tenon is short and does not go through (Fig. 593). This is a common form, and is used a great deal in the best work. It is sometimes called blind mortising, the tenon being known as a "stub" tenon.
- 79. Fig. 594. Mortise and tenon joints are sometimes merely fitted together, but can also be glued (see Gluing), pinned, wedged, or dovetailed and fastened with a key. To pin a mortise and tenon, simply mark a point with square and gauge upon each side of the piece containing the mortise (Fig. 593), fit the tenon in place, and bore in from each side (or in rough work bore right through from one side until the spur appears on the opposite surface) (see Boring). Then drive through a snugly fitting pin and trim off the projecting ends. The pin should be slightly pointed before driving, on the same principle that the end of the tenon is bevelled. It is not necessary to round the pin. An eight- sided one is just as good. Do not use too large pins. In ship-building, bridge-building, and old-fashioned house-framing pins and treenails from 1" to 1¾" or more in diameter, are used. Dowels of various sizes will usually answer for such framing as you may have to do (though a rift-pin is stronger). For such work as pinning a joint in a chair, you will not need anything larger than a ¼" hardwood pin. You must use judgment as to how near the edge to place the pin. If you put it too far from the edge, its hold on the tenon will be weak and the end of the tenon may break out (shear). If you put it too near the edge, the sides of the mortise may tear or split out. Sometimes, particularly in timber work, to insure a snug fit at the joint, "draw-boring" is resorted to (Fig. 594). The hole for the pin is not bored through the tenon as just shown, but is bored a trifle nearer the shoulder of the tenon than the other holes (in the mortise-piece). The result is that when the pin is driven through it draws the tenon-piece down to a snug fit at the shoulder. But this has to be done with judgment. If the hole in the tenon is too much out of line, driving the pin through tends to
- 80. Fig. 596. split (strictly speaking to shear) the end of the tenon, and too much strain is put on the pin. Fig. 595. In the mortising just shown, there are only two shoulders where the tenon begins —that is, the tenon is made by only four cuts. This is good for all common or rough work. In nice work a shoulder is also cut at each edge of the tenon (Fig. 595). This makes a neater-looking joint, as these shoulders cover the ends of the mortise completely. When the joint comes at the end of the mortise-piece, the tenon can extend to the edge on the outside and the mortise be cut clear out to the end, forming an open mortise-and-tenon joint (Fig. 543), or a wide shoulder can be left on the outside of the tenon—the tenon itself being made narrower (Fig. 596). This course is adopted in doors and frames of various kinds (see Fig. 334). Fig. 597.
- 81. Fig. 601. Fig. 598. Fig. 599. Fig. 600. A good way to fasten tenons is to wedge them. This can be done whether the tenon goes through the mortise-piece or only part way, as in a blind joint. The wedges can be driven between the tenon and the ends of the mortise (Fig. 597), or, as is often better, driven into cuts made in the tenon itself, thus spreading the tenon toward the end, dovetail fashion, making it extremely difficult, or impossible, to pull it out of the mortise. Before wedging, the mortise should be cut under or enlarged toward the side on which the tenon comes through (Fig. 598). The wedges can then be dipped in glue and driven as in Fig. 599. To spread the tenons themselves, one or two or even three saw-cuts should be made in the tenon, lengthways and farther than the wedges will extend (Fig. 600). The tenon and mortise having been properly glued, the tenon is fitted in place, and the wedges, previously prepared of some strong wood and tapering quite gradually, are dipped in the glue and driven down into the saw-cuts, thus spreading the end of the tenon into a dovetail until it fills the mortise (Fig. 601). It is often best to drive the outer wedges nearer the edge of the tenon than is shown in Fig. 600, lest the tenon-piece be split.
- 82. Fig. 602. The process is much the same when the tenon does not go through the mortise-piece (Fig. 602). The mortise is undercut as before, and saw-cuts are made in the end of the tenon. The wedges are carefully planned and cut so that, when the tenon is finally in place, they will be of the right size to spread it so as to fit the mortise. The wedges must not be too long, so as to interfere with the tenon being driven home or to break off. When you are sure the whole will go into place and fit snugly, glue everything, start the wedges in the cracks, and drive the tenon quickly to place. This will of course drive in the wedges, which will spread the tenon at the end and fix it firmly. In fact, if well done, you cannot get it out again. There are other forms of mortise and tenon, but they will be seldom required by the amateur. See Joints. Nailing.—To drive nails, hold the hammer near the end of the handle. Do not, as is often done by boys and amateurs, grasp it close to the head. The nearer the end of the handle you take hold, the harder blow you can strike, just as the longer the handle, the harder the blow. Use light strokes—mere taps—in starting the nail. After you are sure it is going straight you can then use more force to drive it home. Do not try to sink the nail-head quite flush with the wood. Leave that for the nail-set. You may think that any slight depression you may make if the hammer strikes the wood will be too
- 83. Fig. 603. slight to be seen, but that is not so, as the slightest dent or depression will probably show in finished work. The head of the hammer should be swung back and forth through an arc of a circle of which the wrist is the centre. Do this carefully and steadily and you will send the nail in quicker and straighter than when you flourish the hammer wildly around in the air and bring it down with a ferocious bang somewhere in the vicinity of the nail, as boys of all ages have been known to do. Now, remembering that the hammer-head will (and should) swing around in an arc of which your wrist is the centre, you must see that your wrist is in such a position that the hammer-head can strike the nail squarely—that is, the hammer-handle, when the head rests squarely on the nail-head, must be in a line parallel with the flat surface of the top of the nail (Fig. 603). If the wrist is much above or below this line, the nail will be struck slantingly, and either be driven crooked or bent (Fig. 604). Fig. 604. First place the hammer in the correct driving position, and then swing it back and forth as nearly in the same curve as you can.
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