Production Steps to Make the Acu-Math 401 Slide Rule
An interview with Eugene Castiglione, former manager of the Mt. Olive
making wood slide rules since 1938 and dealing with the raw material
shortages and allocations during World War II, the Acu-Rule
Co. was ready to develop new products. Magnesium core slide
rules were produced in 1946 and then vinyl
slide rules around 1948. After a few unsuccessful tries their
final choice of a substrate was a material consisting of eight layers of a special, 0.015 inch thick, vinyl film laminated with an adhesive under heat and pressure made by the Bakelite Company of Ottawa,
was sold in a 30 inch by 20 inch piece that was 0.12 inches
At each step there is a chance for damage that will result in a reject. The model 401 averaged a 13% loss with most of it from the stamping and milling operations. Some of these rejects may have been almost finished and both the raw materials and the labor were a loss. Each model of slide rule had a stamping die. These were obtained from the Western Die Co. in St. Louis and were expensive.
The Economics of the Business.
The production models, 400 and 401, had a retail price of $2.00. They were sold to vendors and resellers on terms of 50 / 10 / 5 . This meant a 50 % reduction which reduced the wholesale price to $1.00 and the 10 % reduced it to 90 cents followed by the 5 % left about 85 cents. Also sales terms of 2%10 net 30 gave another 2% if paid for in 10 days - the final bill was due in 30 days. The company would get about 83 cents for a rule. Labor in 1960 was $1.48. The labor force was about 18 people. The cost estimate for this rule was 67 cents so the profit was low. This did not include general overhead of running the business. The overall profit of the company was about 6%.
Based on the same 1960 process a cost estimate to make a #401 today would be about $2.40 and would need to sell for $8.00 to $9.00. Modern technology probably will reduce the cost rather than increase it. Around 2,000 or more rules a day could be made depending on the model. This would put the estimated yearly output at around 600,000 slide rules.
With some professional models scrap was as high as 20%. Some of these rejects may have been almost finished and both the raw materials and the labor were a loss. The more production steps the greater the chance for damage. A slide rule with two color printing and scales on both sides required four hot stamping steps and perfect register. Some higher grade professional models required processing Magnesium (the Magnesium dust being very flammable), assembly with screws and bolts, cursor assembly using 8 screws, two color printing and adjustment for alignment by hand. The higher grade professional models used a thicker 10 layer substrate. Seventeen models were produced. The top of the line was the 1311 selling at retail for $13.95. This was a magnesium core with a single sheet of 0.015 vinyl film laminated to it. Other magnesium rules were the 511 and the 1211. The rules were guaranteed but very few were returned.
The 21 steps to make the #401 slide rule
1. Vinyl stock is cut into blanks.
2. Each edge of the blank is machined.
3. The scales are now applied
4. Inspect for complete printing.
5. Remove excess printing foil
6. Round each corner of the blank.
7. Slice the blank into three strips.
8. Machine the stators
9. Machine the tongue on the slide.
10. Inspect quality, fit, completeness.
11. Place in a gluing jig.
12. Apply a chemical bonding material.
13. Bond the plastic brackets.
14. A twenty minute dry time is required.
15. Apply center line to the cursor.
16. Fit the cursor with a tension spring.
17. Move rule to the packing station.
18. Install cursor and final inspection.
19. Insert rule into a sheath.
20. Pack rule, sheath, manual into box
21. Pack for shipment