[ATM] Re: ATM Digest, Vol 12, Issue 2

[artbianconi@blast.net]

Instrument panels on aircraft work best when they do not have any 
steel parts in them that might affect navigation instruments like 
compasses.

Fastening methods based on the aluminum panel work fine but when 
working on composite structure, I needed something that would be 
structurally sound but more appropriate to the foam core used in 
the composite sandwich. I wound up molding my own threads.

The process is simple enough.

Take a bolt whose pitch and diameter is what you wish to use, and 
wrap it with a tightly wound piece of teflon plumbing tape. Try 
to avoid excessive overlap but do pull the tape tight so that it 
gets down into minor diameter at the bottom of the threaded area.

Paint the thread with whatever resin system you are using and, 
while it is still wet, wrap a layer of fine, one or two ounce 
BID. Follow that with a heavier layer of BID (8 ounce) and then 
slurry a generous amount of wet flox. Let cure. 

When the layup has cured fully, grip the built up region with a 
pair of pliers and simply back out the bolt. It should come out 
easily and the precision of the copied threads should be 
apparent. 

Now simply trim and dress the exterior of your part to fit the 
application and pot it into a suitable cavity. Done.

I've made lots of female threaded anchors this way but not too 
many males. This process is fine for less stressful applications 
where the loads are relatively light and the torque applied to 
the fastener is modest. Unless you are working with an OTA for a 
26" chunk of glass, I see no problems using this method in 
telescopes..

Molding male threads is more difficult. Try filling a nut without 
creating voids. Nuts are shallow. If you need more grip range, 
you must first drill and tap a longer piece of material of 
suitable depth. Obviously, you are not going to get teflon tape 
in that threaded hole but a can of silicon based mold release 
will suffice. I've done it but frankly, it was more of an ego 
thing to test my own limitations than a practical solution to 
anything. Made even more apparent by the fact that you can buy 
threaded fasteners made from damn near any material nowadays.

The need for custom molded female threads is apparent. I don't 
see it for male threads.

Art Bianconi

> 
> Message: 2
> Date: Wed, 1 Dec 2004 11:07:28 -0800
> From: "Bob May" <bobmay@nethere.com>
> Subject: Re: [ATM] truss poles; was: How Big is Too Big?
> To: <atm@atmlist.net>
> Message-ID: <002e01c4d7d9$00e06ec0$1600a8c0@amd>
> Content-Type: text/plain;	charset="iso-8859-1"
> 


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