Thread minor diameters

[NealebParticipant @nealeb]

I regularly use Solid Edge Community Edition for 3D CAD. I would like to add a range of ME threads to the as-supplied thread library. The basic method to do this is pretty straightforward and I can start with a copy of an existing library to give the format which is actually an Excel spreadsheet. There is also documentation which shows the thread data needed for each thread size. This data includes the minor thread diameters for both internal and external threads. I am fairly sure that I know what is meant by these terms but I cannot find a way to calculate them which gives results consistent with the existing library data. Google searching comes up with a whole series of useful little diagrams showing details of thread parameters although I have not yet found one that clearly indicates if the, for example, nominal thread diameter is to the crest of the finished thread, the notional top of the triangular thread before crest rounded, or some other point. I am aware that the formulae given for things like thread depth include a sin60 or similar (as they are all showing UN or metric threads) which need recalculating for a 55deg thread angle.

Anyone have a pointer to something definitive on this? I’m happy to do the sums (and the spreadsheet nature of the thread libraries makes this easy) but can’t quite get my head around interpreting the meaning of the the various thread parameters. Made more complicated by the fact that no-one else seems to bother quoting these minor diameters in thread tables! What am I missing?

 

[DC31kParticipant @dc31k]

ME threads are of Whitworth form.

Whitworth threads are detailed in BS 84, pdf copies of which can easily be found online.

The BS contains all necessary information to answer your question.

For modelling purposes, the BS gives a baseline figure to which you then have to apply a fit class.

[DiogenesParticipant @diogenes]

Redundant – DC types faster

 

 

[JasonBModerator @jasonb]

This sort of thing, the three columns are Major Dia, Pitch Dia and minor Dia

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