Comments by "mpetersen6" (@mpetersen6) on "The HIDDEN Screws of PRECISION" video.

@sjb3460 The hard part of cutting Whitworth threads on a lathe is grinding the tools. Not the 55° included angle. But grinding the proper tip radius and the radii that form the proper crown on the top of the thread. Plus some of the Whitworth pitches are not normally found in the Quick Change Gear Boxes of non British lathes. 19 tpi for one. Also it was very common for machine tool builders to have their own special thread pitches. Brown and Sharpe used to use things like 1/4-22 or 1/4-32 (1) for the screws used in their screw machines. Also those really nice Swiss MultiFlex tool posts use things like 7mm, 9mm or other odd sizes not normally found even in the catalogs of industrial supply houses. It's called "buy our parts". 1) I've got a tap for that one
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@tonywilson4713 In the US the standard reference book is Machinery's Handbook. Mine is close to 50 years old and is still useful. In fact it probably has info that is no longer listed in newer editions. We used to make a lot of replacement parts eith gear teeth cut to the Fellows Stub Tooth system. The Pitch Diameter was based on one Diametral Pitch while the overall height of the gear tooth and the OD was derived from the next smaller gear tooth profile. A gear would be expressed as 48T-10/12DP.
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