Types --

Board measure, carpenter, cordage, desk, drafting, ell, engineer, folding, lumber, log, machinists, surveying, tailors, shrink rules, cork gauge & square.

The carpenter's rule

The slide rule uses the same principles as Edmond Gunter's logarithmic scale. It was developed by William Oughtred in the early 1630's. In the early 1800's Joshua Routledge combined a 12 inch brass slide containing the logarithmic scales with an ordinary 2 fold 2 foot rule. The brass slide was engraved with two scales. These scales were the same, one over the other, each consisting of a two period logarithmic line of numbers. This slide was placed between two scales engraved in the wood base of the rule. The scale above the slide was the same two period logarithmic line of numbers. The scale below the slide was a single period logarithmic line of numbers. From top to bottom these were labeled the A, B, C & D scales.

At that time the Gunter scale was in common use for navigation calculations. The logarithm of a number was usually taken from the scale using a pair of dividers. By laying out on a line the logarithms of numbers, multiplication and division could easily be done with an accuracy of about 1 percent. Constants or often used values were marked in the Gunter scale using brass pins. These pins were called gauge points. Gauge points would have been very complex for the Routledge rule since engineering work required many different values. Routledge added a table of gauge points commonly used in engineering calculations to the ruler. This rule became known as the Routledge engineer's rule

Sir William Armstrong, a hydraulic engineer, probably was responsible for the variation to the Routledge rule that became the carpenter's rule. The A, B & C scales remained the same, however the D scale, still a single period log scale, was changed such that the numbers ran from 4 to 40 (.4 to 4, 40 to 400 or any other decade of numbers). This had the effect of moving the number 12 closer to the center of the scale. 12 is a common gauge point in timber measuring. This D scale is commonly refered to as the GIRT LINE and is so marked on most carpenter rules. The carpenter would not normally use the table of gauge points thus that area of the rule usually contains draughting scales as well as the eight square scale used for spar making.

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The cordage rule

The cordage rule was usually made of boxwood and brass (some examples of all brass, or aluminum and brass are seen). Usually 2 or more inches wide by 5 or more inches long and about 1/4 inch thick. These rules contained a caliper to indicate either diameter or circumference of large wire ropes or fiber lines (ropes). They usually are marked with the name of a rope maker or distributer. While often thought to be advertising pieces, they were a very valuable tool. These rules contained tables relating the diameter or circumference of ropes to either breaking strength or the weight of certain length coil (usually 100 or 200 fathoms). The below table is taken from a boxwood and brass KERBY & BRO MAKERS 51 FULTON ST NEW YORK, also marked on the back side with PLYMOUTH CORDAGE CO / NORTH PLYMOUTH / MASSACHUSETTS.
MANILA CORDAGE
SIZEWEIGHT
CIRDIAPER COIL OF
INCHESINCHES200 FATHOMS
6 THD1/4 INCH22
9 "5/1629
12 "3/844
15 "3/8 FULL50
1 1/4 IN7/1665
1 1/2 "1/290
1 3/4 " 9/16125
2 "5/8 160
2 1/4 "3/4 198
2 1/2 "13/16 234
2 3/4 "7/8 270
3 "1 324
3 1/4 "1 1/16378
3 1/2 "1 1/8 432
3 3/4 "1 1/4 504
4 "1 5/16 576
4 1/4 "1 3/8 648
4 1/2 "1 1/2 720
4 3/4 "1 9/16 810
5 "1 5/8 900
5 1/2 "1 3/4 1080
6 "2 1296
6 1/2 "2 1/8 1512
7 "2 1/4 1764
7 1/2 "2 1/2 2016
8 "2 5/8 2304
8 1/2 "2 7/8 2590
9 "3 2915
9 1/2 "3 1/8 3240
10 "3 1/4 3600

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The shrink rule

Average shrinkage of castings
from: Stanley Tools Catalog No. 139, September 1, 1939
Material Shrinkage inch per foot
Cast Iron 1/8Many different special rules have been used over the years. For example molten metal shrinks when it cools, forming a casting that is smaller than its mold. Therefore the mold is made an amount larger to offset the shrinkage. Patternmakers used these specially made rules for each type of metal they poured. Thus a 2 foot shrink rule for cast iron is actually 24 1/4 inches long.
Brass 3/16
Steel 1/4
Malable Iron 1/8
Zinc 5/16
Tin 1/12
Aluminum 3/16
Britannia 1/32
Lead 5/16
Copper 3/16
Bismuth 5/32
Tera Cotta 3/4

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Lengths of Standard Corks from cork gauge by
Mundet Cork Corp, Brooklyn N.Y.
ShortsRegularsExtra Longs
SizeLengthSizeLengthSizeLength(length in inches)
0 3/8 0 1/205/8Stoppers were gauged by the diameter of the large end. The adjacent table gives the correct length for each size diameter stopper for the commonly used lengths of Shorts, Regulars and Extra Longs. The cork gauge has graduations at a 16th inch spacing; starting at 7th mark (3/8 inch) and continuing on alternate marks are: < 0 >, < 2 >, ..., < 26 >.
1 1/2 1 5/813/4
2 1/2 211/162 3/4
3 1/2 3 3/43 13/16
4 1/2 413/164 7/8
5 5/8 5 7/8 5 1
6 5/8 615/16 6 1 1/16
7 3/4 7 1 7 1 1/8
8 3/4 81 1/168 1 1/4
9 3/4 91 1/8 9 1 1/4
10 to 26 1 10 to 151 1/4 10 to 151 1/2
16 to 261 1/2
Sizes 21, 23, 24 were not used.

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From Ken Roberts' reprint of Lufkin 1888 catalogue,
p. 24, Comparison of Log Tables (partial) number of board foot of lumber in a 16 foot log of given diameter:
Diameter 10 11 12 13 20 30 40
Scale
Doyle's36 49 64 81 256 676 1296The number of board feet of lumber attained from a sawn log depends on the diameter and length of the log. A log rule, used to measure board feet as a function of diameter was used. Factors like species (taper), sawing method, local customs all defined variations such that many different scales evolved and many are still used today. Most states have laws defining which scales are to be used for inventorying or quoting saw logs. I am aware of at least 28 different scales. Some are listed in the adjacent table.
Scribner49 64 79 97 280 657 1204
Favorite 37 48 64 82 248 632 1160
Baxter 56 69 84 100 250 582 1052
Two-Thirds58 70 85 100 237 533 944
Dusenberry40 54 68 80 229 567 1054
Cumberland River47 57 68 80 190 427 759
St. Louis Hardwood59 72 85 100 237 533 947
Northwestern61 70 77 97 248 632 1160
Decimal 6 7 8 10 28 66 120
Spaulding's Pacific Coast50 63 77 94 276 656 1185

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Explanation of Symbols used in Table of Eagle Squares
fbo Face of Body Outside bbo Back of Body Outside
fbi Face of Body Inside bbi Back of Body Inside
fto Face of Tongue Outside bto Back of Tongue Outside
fti Face of Tongue Inside bti Back of Tongue Inside

Squares sold by Eagle Square Company, South Shaftsbury, Vermont
POLISHED SIZE IN INCHES GRADUATIONS TO INCH HOW MARKED
No. List /doz. Body TONGUE FACE BACK
Wide Long fbo fbi fto fti bbo bbi bto bti
100 $21.00 2x24 1 1/2 or 1 3/4 16, 17 & 18 16 8 16 8 12 32 12 10 Brace, 100th Scale, 8 Square, Essex's Board Measure
1 $20.00 2x24 1 1/2 or 1 3/4 16, 17 & 18 16 8 16 8 12 8 12 10 Brace, 100th Scale, 8 Square, Essex's Board Measure
2 $18.00 2x24 1 1/2 or 1 3/4 16, 17 & 18 16 8 16 8 12 4 12 4 Brace, 100th Scale, 8 Square, Essex's Board Measure
3 $17.00 2x24 1 1/2 or 1 3/4 16, 17 & 18 16 4 16 4 12 4 12 4 Brace, 100th Scale, 8 Square, Essex's Board Measure
4 $16.50 2x24 1 1/2 or 1 3/4 16, 17 & 18 8 4 8 4 12 4 12 4 Brace, 100th Scale, 8 Square, Essex's Board Measure
5 $16.00 2x24 1 1/2 or 1 3/4 16 8 4 8 4 12 12 4 Brace, 100th Scale, 8 Square, Essex's Board Measure
6 $15.50 2x24 1 1/2 or 1 3/4 16 8 4 8 4 4 4 4 Brace, 100th Scale, 8 Square, Essex's Board Measure
14 $15.00 2x24 1 1/2 or 1 3/4 16, 17 & 18 8 4 8 4 4 4 4 Brace, 100th Scale, 8 Square, Essex's Board Measure
RAFTER SQUARES
No. List /doz. Body TONGUE FACE BACK
Wide Long fbo fbi fto fti bbo bbi bto bti
100R $53.00 2x24 1 1/2 or 1 3/4 16, 17 & 18 16 8 16 8 12 32 12 10 Rafter, Brace, 100th Scale, 8 Square, Board Measure
1R $47.00 2x24 1 1/2 or 1 3/4 16, 17 & 18 16 8 16 8 12 8 12 8 Rafter, Brace, 100th Scale, 8 Square, Board Measure
3R $41.00 2x24 1 1/2 or 1 3/4 16, 17 & 18 16 4 16 4 12 4 12 4 Rafter, Brace, 100th Scale, 8 Square, Board Measure
OCTAGON RAFTER SQUARES
No. List /doz. Body TONGUE FACE BACK
Wide Long fbo fbi fto fti bbo bbi bto bti
100A $60.00 2x24 1 1/2 16, 17 & 18 16 8 16 8 12 32 12 10 Rafter, Octagon Framing, 100th Scale, 8 Square, Brace
BRIDGE BUILDERS
No. List /doz. Body TONGUE FACE BACK
Wide Long fbo fbi fto fti bbo bbi bto bti
15 $144.00 3x24 1 1/2 18 16 8 16 8 12 8 12 10 One inch slot in body, graduated to 1/8ths
STONE CUTTERS
No. List /doz. Body TONGUE FACE BACK
Wide Long fbo fbi fto fti bbo bbi bto bti
16 $36.00 2x30 1 1/2 24 8 4 8 4 8 4 8 4
17 $54.00 2x36 1 1/2 30 8 4 8 4 8 4 8 4
18 INCH SQUARE
No. List /doz. Body TONGUE FACE BACK
Wide Long fbo fbi fto fti bbo bbi bto bti
18 $15.00 1 1/2 x 18 1 12 16 8 16 8 12 8 12 8
12 INCH SQUARE
No. List /doz. Body TONGUE FACE BACK
Wide Long fbo fbi fto fti bbo bbi bto bti
10 $11.00 1 1/2 x 12 1 8 8 4 8 4 12 4 12 4
11 $10.50 1 1/2 x 12 1 8 8 4 8 4 4 4 4 4
12 $12.50 1 1/2 x 12 1 8 16 8 16 8 12 8 12 8
52 $13.50 1 1/2 x 12 1 8 16 8 16 8 12 32 12 10
MACHINISTS
No. List /doz. Body TONGUE FACE BACK
Wide Long fbo fbi fto fti bbo bbi bto bti
40 $8.00 1 x 6 3/4 4 32 8 32 8 12 8 12 8
41 $7.50 1 x 6 3/4 4 16 8 16 8 12 8 12 8
TAKE DOWN
No. List /doz. Body TONGUE FACE BACK
Wide Long fbo fbi fto fti bbo bbi bto bti
100 $31.00 2 x 24 1 1/2 16, 17 & 18 16 8 16 8 12 32 12 10 Brace, 100th Scale, 8 Square, Essex's Board Measure
100R $36.00 2 x 24 1 1/2 16, 17 & 18 16 8 16 8 12 32 12 10 Brace, 100th Scale, 8 Square, Rafter, Board Measure
100A $36.00 2 x 24 1 1/2 16, 17 & 18 16 8 16 8 12 32 12 10 Brace, 100th Scale, 8 Square, Rafter Octagon Framing
FLAT STEEL SQUARES
21 $6.00 1 1/2 x 24 1 12 8 8 STEEL

From 1817 until about 1880 these squares were made of iron. Since 1880 all squares have been made of steel, although the original name of iron has clung to them.
22 $7.00 1 1/2 x 24 1 12 8 8 4 4
24 $8.50 2 x 24 1 1/2 12 8 8 4 4
31 $6.75 1 1/2 x 24 1 12 8 8
32 $7.75 1 1/2 x 24 1 12 8 8 8 8
34 $9.25 2 x 24 1 1/2 12 8 8 8 8
Derived from Eagle Square Company Catalog.

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© 1996, 1997, 2016 Philip A. Cannon All Rights Reserved
Old_tool/eagle updated February, 2016