Woodworker's Journal 1984-8-6, страница 21

board surface. This method is not as economical as plainsawing, since it results in more waste. As mentioned earlier, however, with some species of wood, especially oak, the pronounced medullary rays that quartersawing brings out, make for unusually attrac-

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tive figuring on the board surface. If there is an advantage to quarter-sawing lumber, it is that there is iess shrinkage across the face of the board and therefore less of a tendency toward cupping.

Wood Shrinkage and Warping

Though wood has its advantages over steel and other materials such as plastics, it is not nearly as stable in terms of dimension. Immediately after a tree is cut, the wood will begin to lose moisture into the atmosphere. Consequently, the wood shrinks. Conversely, even kiln-dried boards will expand slightly when they are subjected to an atmosphere of increased humidity. This is why in summer, when there is higher humidity, drawers stick and doors won't open. In winter, especially in homes using hot air or wood heat, boards can shrink and occasionally even crack. Chairs may get wobbly, panels may rattle in their frames, and pegs may loosen in their holes. There are three basic types of shrinkage, radial, tangential and longitudinal.

Radial shrinkage reduces the thickness of the annual rings. With plain-sawn lumber radial shrinkage will affect the board thickness, as seen in Fig. 3A. With quartersawn wood radial shrinkage affects the width of the board (3B).

How great can radial shrinkage be? For a freshly cut piece of white oak, if it is dried to 0% MC, the percentage of shrinkage will be about 4'/i%. For a piece of white pine, shrinkage will be about one half of that, or 2%.

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The type of shrinkage that a woodworker must be most aware of, however, is tangential shrinkage. This affects the length of the circumference of the rings. The classic illustration of this is a thin disc cut as a cross section of a log. A saw cut is then made from the outside to the center of the disc, and the disc is left standing upright in the sun to dry. As the moisture begins to evaporate into the atmosphere, the saw cut begins to open up (Fig. 4).

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Tangential shrinkage also answers a question asked by many woodworkers: Why do boards cup opposite to the curvature of the rings? Tangential shrinkage is the most common problem with plainsawn lumber. It is of particular concern to woodworkers because it affects board width to a significant degree.

How great is tangential shrinkage? For the same woods, oak and pine, reduced to zero MC, the percentages are 8.8% and 6.1% respectively.

The third type of shrinkage is longitudinal, or along the length of the board. The percentage of longitudinal shrinkage is usually between . 1 % and

(continued on next page)

Woodworkers' Hardware ORDER FORM

Qty- Total

TH^jprO Birch Mug Peg

-——CJ s ,22/ea._

Birch Shaker Peg

s .25 ea.„__,

Oak Shaker Peg

Birch 6 Inch _Furniture Spindles s>o^a. $ .42 93. _

a 1/2 inch

- 3 .51 « a.

*S4 Galley Spindle

si.50/10.

2 Inch

.Wood

3/4* T/S" 1"

11/4" 1 1/2"

Wheels

T5r»ii£ $3.57/C_ S4.77/C_ fB^MiS S5.00/C_

sTsra^'C se,oi/c_ £T»?»4/C SII.OI/C_ ^ ________ a" $ia.oo/c_

tf¹ ri _Ax|_e Peg

Fits 1"lo2" Wh»»t

Wood Cargo oil Drum

"Wvaj. 10 $2.31/ io_ Milk Can

Jireo;io SI.BO/IO_ Pickle Barrel

as: s^^oo $i.3i/ui_

Screw Hole Buttons

3/fl" S1.74/C_

1/2" SlTVM^C S1.77/C_ Dowel Pins 3/s"*2" S1.77/C_

wood 3/4" sTrs«iio s.90/10.

Knobs S7.77/C.

,1" flriaop si.4o/io_

S2"T^WLi.C Si 2.04/C

_1/4- sTwao $i.so/io_ si3.eo/c_

w 'Screws ¹ 3'4'JWaaO Sz.20.10_

Saw Tooth Hangers

ij-C S4.75/C.

Picture Hanger

"Sriaa^c S4.i7/c_

,Clock Movements w/Hands 073 sflrsoja. SS.4B/M.

S29.70/f_

Lazy Susan Bearing

3' S ,69/e»._

S ,9S'98._

SI,73/M..

Brass Plated Candle Cup

S3.oo/1 o S29.40/C, Coat and Hat Hook SzTt*/^. S1.87/ea._ Brass Wreath

S~B~SO^JO S5.10 10_ Brass Anchor

Slrso-LIQ S3.30 10. Brass Pit. Eagle S"T^«~J0 S2.16'10_

Escutcheon Pins _ Brass Pins lor Above .57/C„

#929 Butt Hinge

SITW^LS S1.08/10_

■f F1 24 Screw lor Above

$2.4 0/c_

Clipboard Clips

3" $ .3 5/sa.__

6" S 59'ea._

Plastic Shelf Pins S5.40/C

________ Hoi. £ a 100

CalHloa S 1.00 or l'«0 wllti C'dtr Total Ordar _

Q Minimum Order !■ S2S.OO WN RM.- b » Ta. _

Order Amount : Shipping : Shipping _

S35.00 (0 S49.99 S3.S0 _{Tq|b1 EncloBad} ___

s so.oo to tee.as S4.S0 —----

Owe, S 100.00 S5.00 Qvna □«nHr Cars

GUARANTEE!

SH3NAIIJBE _

r !■I.' _

NAM? __

ADDRESS . STATE

MEISEL HARDWARE SPECIALTIES

P.Q Bo» 258 J . Wound. Minnesota 55364 • <612) 472-5S44