Barth's gear slide rule
Datecopyright 1902
Inventory Number1990-4-0033
ClassificationSlide Rule
Subject
Maker
Carl G. Barth
1860-1939
Associate Name
Frederick W. Taylor
1856-1915
Cultural Region
Place of Origin
Dimensionsslide rule: 1 × 17 × 17 cm (3/8 × 6 11/16 × 6 11/16 in.)
box: 2 × 19.5 × 19.5 cm (13/16 × 7 11/16 × 7 11/16 in.)
box: 2 × 19.5 × 19.5 cm (13/16 × 7 11/16 × 7 11/16 in.)
Material
Accessoriesstorage box; instruction booklet in instrument file
DescriptionThree off-white circular paper discs and one transluscent yellow rider (celluloid?) joined by a brass bolt with moveable clamping nut.
Two scales are printed around the circumference of the bottom disc. "Tangential Load on Gear in Pounds" carries values from 30 to 30,000. Adjacent to this scale is a scale for "Number of Teeth in Gear," divided vertically. The top portion, labeled for "Cycloidal and 15° Involute Systems," carries values from 12 to 150. The bottom portion is itself divided horizontally. The left-hand side, for "Radial Flank System," carries values from 12 to 120. The right-hand side, for "20° Involute System," carries values from 12 to 300.
Part of the circumference of the middle disc is printed with three scales, stacked vertically. The top scale, "Number of Teeth per Inch of Diameter," carries values from 0.5 to 12. The middle scale, "Circular Pitch," carries descending values from 6'' to 1/4''. The bottom scale, "Face," ranges from 3/4'' to 20.''
One portion of the top disc has a diameter slightly larger than that of the middle disc. Around its circumference is a scale for "Circumferential Velocity of Gear, in Feet per Minute," with descending values from 5000 to 0. Around the circumference of the smaller (in diameter) portion of this disc is a scale for "Permissible Stress on Material at no Velocity, in Pounds per Square Inch of Section," carrying descending values from 100,000 to 400.
Two scales are printed around the circumference of the bottom disc. "Tangential Load on Gear in Pounds" carries values from 30 to 30,000. Adjacent to this scale is a scale for "Number of Teeth in Gear," divided vertically. The top portion, labeled for "Cycloidal and 15° Involute Systems," carries values from 12 to 150. The bottom portion is itself divided horizontally. The left-hand side, for "Radial Flank System," carries values from 12 to 120. The right-hand side, for "20° Involute System," carries values from 12 to 300.
Part of the circumference of the middle disc is printed with three scales, stacked vertically. The top scale, "Number of Teeth per Inch of Diameter," carries values from 0.5 to 12. The middle scale, "Circular Pitch," carries descending values from 6'' to 1/4''. The bottom scale, "Face," ranges from 3/4'' to 20.''
One portion of the top disc has a diameter slightly larger than that of the middle disc. Around its circumference is a scale for "Circumferential Velocity of Gear, in Feet per Minute," with descending values from 5000 to 0. Around the circumference of the smaller (in diameter) portion of this disc is a scale for "Permissible Stress on Material at no Velocity, in Pounds per Square Inch of Section," carrying descending values from 100,000 to 400.
Signedon top disc: Strength of Spur Gears / According to Wilfred Lewis. / Carl G. Barth.
Inscribedon back: Barth's Gear Slide Rule / COPYRIGHT, 1902, BY CARL G. BARTH
Curatorial RemarksIdentical to 1990-5-0003;
Similar in function to rectangular gear slide rules dated 1904, see 1990-4-0011 and 1990-4-0012;
Philadelphia address printed on instruction booklet.
FunctionFor calculating the strength (in load in pounds) of spur gears.
The user first aligns the rider with the appropriate value on the "Number of Teeth in Gear" scale on the bottom disc. Then, using the finger slot on the back of the bottom disc, he rotates the middle disc to align the appropriate pitch value (on either the "Number of Teeth per Inch of Diameter," or "Circular Pitch" scales, according to the gear type) with the rider.
Tightening the clamping nut to hold the bottom two discs in alignment, the user then moves the rider to the appropriate value on the "Face" scale on the middle disc. Then, after loosening the clamping nut, he rotates the top disc so that the appropriate value on the "Permissible Stress" scale coincided with the rider. Again he tightens the clamping nut.
The user finally moves the rider into alignment with the appropriate value on the top disc's "Circumferential Velocity" scale. The coincident value of the "Tangential Load on Gear in Pounds" scale on the bottom disc equals the strength of the gear in question.
According to the instruction booklet (in instrument file), this slide rule derives from a formula published by Wilfred Lewis in 1893. See "Primary Sources" for citation.
Barth also produced straight (rectangular) gear slide rules.
The user first aligns the rider with the appropriate value on the "Number of Teeth in Gear" scale on the bottom disc. Then, using the finger slot on the back of the bottom disc, he rotates the middle disc to align the appropriate pitch value (on either the "Number of Teeth per Inch of Diameter," or "Circular Pitch" scales, according to the gear type) with the rider.
Tightening the clamping nut to hold the bottom two discs in alignment, the user then moves the rider to the appropriate value on the "Face" scale on the middle disc. Then, after loosening the clamping nut, he rotates the top disc so that the appropriate value on the "Permissible Stress" scale coincided with the rider. Again he tightens the clamping nut.
The user finally moves the rider into alignment with the appropriate value on the top disc's "Circumferential Velocity" scale. The coincident value of the "Tangential Load on Gear in Pounds" scale on the bottom disc equals the strength of the gear in question.
According to the instruction booklet (in instrument file), this slide rule derives from a formula published by Wilfred Lewis in 1893. See "Primary Sources" for citation.
Barth also produced straight (rectangular) gear slide rules.
ProvenanceThe papers and slide rules of Carl G. Barth and his son, J. Christian Barth, were transferred to the Baker Library of the Harvard Business School by J. Christian Barth in 1961.
The slide rules were transferred from Harvard Business School to the Collection of Historical Instruments in 1980.
Historical AttributesThis is part of a set of slide rules for machine shops designed by Carl G. Barth under Frederick Winslow Taylor's system of scientific management. Given the characteristics of a particular machine and a depth of cut, for example, a shop manager could quickly calculate the most efficient speed and feed settings using one of Barth's speed and feed slide rules. Other objects in the collection include slide rules for helical springs, belts, and gears, as well as jigs for making slide rules.
Carl G. Barth
Date: copyright 1902
Accessories: storage box; instruction booklet in instrument file
Object number: 1990-5-0003
Carl G. Barth
Date: circa 1904
Accessories: storage box
Object number: 1990-5-0020
Carl G. Barth
Date: circa 1904
Accessories: storage box
Object number: 1990-5-0021
