[time-nuts] Machining some aluminum help!

Bob kb8tq kb8tq at n1k.org
Thu May 18 20:19:03 EDT 2017

> On May 18, 2017, at 8:13 PM, jimlux <jimlux at earthlink.net> wrote:
> On 5/18/17 2:36 PM, Chris Albertson wrote:
>> It would be easy to re-design the job for cheaper machining..  Do you
>> really need to tap the holes?  You might use self taping screws.  Id the
>> would work then you can do the work yourself with just a hand drill.
>> OK it you must use machine threads and they must be #4 size try "rivets"
>> these work like pop rivets but leave a hollow thread insert in the hole
>> that will take screws.  Takes all of 5 seconds to install a thread hole.
>> Think again about threading aluminum.  It is not very strong, it would be
>> easy for an end user to strip the #4 threads.  Better to use the rivet or
>> other steel thread insert.    Even native nuts  installed with flush rivets
>> is better
> Interestingly enough, for 4-40 hardware, the screws fail before the aluminum does.  The area of the thread engagement is quite a bit larger than the cross section of the fastener that is not thread.

There are a lot of variables involved. Run the screws in and out of the aluminum a number of times and 
the holes will fail first ….There are other gotchas as well.


> For large fasteners, where the thread depth is a smaller fraction of the fastener diameter, this may not be the case (as anyone who has stripped the threads on an aluminum cylinder head with a steel sparkplug will know, in a deep and visceral way).
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