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Strength when threading into Aluminium

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picclock:
I am using some 6mm Steel allthread into an aluminium block. The minimal allthread strength is 1000 lbs yield, about 6x my working load. However I am a bit unsure as to the depth of thread needed to transfer the load without fear of stripping the thread. I know that conventional wisdom is 4 threads, but I have always taken this to be with similar materials, and I normally allow double that if the design will tolerate it.

So the question - How is the number of threads required calculated when threading into different materials ?

For this particular case I have a workaround but the information would be useful to know.

Many Thanks

picclock

Davo J:
I have no idea of a chart etc, but I would be going 6 at least. You can always drill and tap it bigger and use helicoils into it. They come in all sorts like stainless, brass etc and you locktite them in, so you then have a good strong thread.

Dave

BillTodd:
http://www.gizmology.net/nutsbolts.htm

picclock:
@ DaveJ
The current design allows up to 16mm for threading, and I can also mill out a recess for a steel flanged nut at the cost of 6mm depth. However, although I feel fairly safe with my 16mm (16 threads in M6), it would be nice to have a more informed answer as to how many threads are really necessary.

@ BillTodd
I looked up the link you posted and whilst it has a lot of information the mixed metals threading issue doesn't seem to be covered, if I've somehow missed it a pointer would be welcome !

Best Regards

picclock

Davo J:
Thats 16 threads, you would break the thread rod pulling those threads out of it.

Dave

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