jigs and fixtures

I am teaching "Design of Jigs, Fixtures and press tools". For Jig
design I am referring "jig and Fixture design" by Edward G.Hoffman IV
edition. In that, for joining two plates (design of Plate jig for
Housing cover, Page No.165 fig.11-15), 4 cap screws & 3 dowel pins are
used. In the same way, in page no. 195 fig.13-12, 2 cap screws & 2
dowel pins are used. Can you explain, how to select the size of cap
screws & dowel pins.
Thanks in advance
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My approach would be to roughly figure the loads on the pieces involved and look up in Machinery's handbook the strength of various sized cap screws vs. size. That's for the tension loads. You'd then figure out your shear loads for the dowel pin sizes. Allow a suitable margin of strength, 5x, 10x(if you're paranoid) and you should be able to come up with something that would work. Chances are that with lightly loaded drill jigs that even the smallest screws and pins will work, it's just easier using something larger. This is like 1st and 2nd year ME stuff.
Alternative answer, look at what's been done before in a similar situation and use the same-sized fasteners.
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Stan Schaefer
snipped-for-privacy@americanisp.net (Stan Schaefer) wrote in news: snipped-for-privacy@posting.google.com:
Totally agree, however, to add one more point, look at the thickness of the material the bolts and dowels will be installed in after the holes are made. Does you no good to have a high strength bolt/dowel set-up if the material to either side of the hole will fail first.
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