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Round Threads
3

Round Threads

Round Threads

(OP)
I am working with a weak composite where I have to drill a hole and tap it.  From there I have to make a plug from the same material to fill the hole.  Due to how brittle the material is I cannot use a standard UNC thread.  I have looked into using ACME threads but my manager suggests a round thread similar to those found on a light bulb where there is not a sharp corner.  Does anyone know what kind of thread this is?  Or something similar?

RE: Round Threads

Well, the Whitworth thread http://www.boltscience.com/pages/screw4.htm
has a radius at both the peak and valley of the thread.

Seems like it would be far better to put a chunk of metal in the mold during the layup so that you could tap metal instead of whaever.

RE: Round Threads

You can try the British Standard Whitworth thread. It may be difficult to find Whitworth taps and dies but, if need be, you could make them.  See attached link.
http://www.sizes.com/tools/thread_whitworth.htm

RE: Round Threads

Your best option might be to design your own thread which means screw cutting your own plugs and making your own tap -not a particularly difficult undertaking.

RE: Round Threads

I agree with Artisi, design your own thread specifically. A tap is just a bolt with a groove cut in it ground, to a point, if push comes to shove.

Cheers

Greg Locock

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RE: Round Threads

We had an old component at my last place that actually used a thread form similar to on plastic bottles etc, can't remember the details but it was rounded as it was actually a deformed sheet metal part.

If I recall correctly you can have a radius at the root of UN threads by choosing UNR (think that's right) but it probably isn't enough of a rad for what you're dealing with.

KENAT, probably the least qualified checker you'll ever meet...

RE: Round Threads

Whitworth is a pain...

www.britcycle.com

Ask any old Triumph owner.

RE: Round Threads

What are the materials in the composite? Do I understand correctly the plug is the same composite and remains solid?If I was filling the hole with a solid plug I'd just roughen and clean both items and bond the plug in place. Tapping glass type composites just seems to mess up the glass fibers in the material.

RE: Round Threads

The dimensions for a light bulb thread are in the Machinery's Handbook.

Don
Kansas City

RE: Round Threads

(OP)
Granted I have little experience with composites, as well as the material being discussed is currently proprietary.  I can say that it is no a glass based composite and the reason which a sealed plug in not being used is because the material has a limited lifespan and we are trying to minimize replacement time and complexity.

Thanks everyone for your advice.  I think I have the problem under control.

RE: Round Threads

OK I have to ask, are you dealing with a liquid commodity here? IF so you'll need to look at a tapered thread.

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