I think that you'll find that it makes bugger all difference. The feedscrew will have worn to something slightly different anyway.

Make it 29 1/2 degrees and then calculate the maximum possible error in both cases. Chew on that number a bit in the context of every other error and uncertainty in the making process, including the wear.

It made it very easy (and thus more economic) for Messers Box, Den and Col.

No need to keep two sizes of leadscrew blank in stock. No need for inventory management so they did not get mixed up. Similarly for the cutting tools. Simllarly for the workholding devices. Agile manfacturing ability – at the flip of a lever on the machine either language leadscrew is produced. No need to make a batch of 20 and then call the toolsetter to alter the machine.

In prodcution manufacturing, cost is an issue. Why do so many French cars have M7 threads? Because M6 is too small to work and M8 in million-volume is too costly.

It would be interesting to look at some of the European manufacturers' machines that were available in imperial form and see what they did (e.g Deckel & Aciera mills, Schaublin lathes). Also interesting would be to look at current far-East machines and see what they do – they sell into both SI and Inch markets.

I have just produced 4 leadscrew nuts for the museum's drill mill in 2.5 mm pitch. The threadform is trapezoidal for most metric pitches which has a 30 degree flank angle. The er/ir16 inserts that I used would not be suitable for a 5/8" or 16mm size, the leadscrews I made them for are around 22mm diameter, and 3/4" or 20 mm leadscrew diameter would be the minimum size that they can enter.

There are ready made nuts available from an ebay advertiser, the price varies accordingly to how sophisticated the nuts are, but are worth a look.

Edited By old mart on 08/05/2022 16:50:26