Round Threads 3

[mullins]

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?

 

[MintJulep]

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.

 

[vzeos]

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

 

[Artisi]

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.

 

[GregLocock]

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

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[unclesyd]

Travel down to page 12 of 15 and look at the crane hook thread. It has a DIN spec. This is the strongest of the common "Knuckle" threads.

http://www.hexagon.de/dose/dose-1e.pdf

Look down the page as there are several standardss for round threads including the Edison Light bulb Thread, again known as a Knuckle thread.

http://mdmetric.com/fastindx/t44u.pdf

 

[deanc]

http://www.tapcousa.com/promotions.asp

Call them. Are you willing to pay for a special tap?

Have you considered thread inserts?

 

[KENAT]

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...

 

[NickE]

Whitworth is a pain...

http://www.britcycle.com

Ask any old Triumph owner.

 

[Tmoose]

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.

 

[Fabrico]

Have you tried some of the taps for hard steel or cast iron?

http://www.besly.com/stdtaps.htm

 

[eromlignod]

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

Don
Kansas City

 

[mullins]

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.

 

[11echo]

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