For those who care about tensile strength of screws, the root of screw threads very significant affects screw tensile strength!
A sharp bottom V is a stress concentrator/riser, and defines the minor diameter of the screw. Rounded is better, as is maximizing the effective diameter of the screw.
Conversely, the top of the thread has esentially nothing at all to do with tensile strength.
And we are talking about SAE (60 deg) and British (55 deg(?)) V type threads here.
Buttress threads are pretty cool, but who knows about these?
Jim I
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On Jan 10, 2019, at 1:05 PM, Charles <xlch58@...> wrote:
A full profile insert makes the entire thread, flank, root and crest. Because the root and crest width varies by pitch, they are only good for a limited number of threads. A partial profile essentially only cuts the flank and root, but you have to finish the crest. A pass with a file will do it generally, depending on how picky the thread is. A tool with an 8-48 tpi range is not going to have the proper root width across that whole range, it is only going to be right for the top end of that range (48). From watching youtube, only a limited number of the "machinists" there bother with root or crest shape, using a sharp v tool for everything. Whitworth and some other threads have a radius at root and crest.
