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Screwing into Aluminum

bjdecker

bjdecker

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One of the weak spots in the RV kits is the attachment of certain fairings with screws directly into longerons. If you're successful in drilling & tapping the longeron, and installing the screw without stripping the threads out initially, it's just a matter of time until you do.

Forget to set the correct torque or sneeze while turning the screwdriver, and so forth, and the screw will just spin-spin-spin. And your Dad's tip about backing it out 1/4 turn *after* it becomes loose, wasn't a good idea after all :(

This is similar to the inserts used for sparkplugs, etc. in other aluminum structures. This works very well, and they have small sizes available (4-40, 2-56 etc.)

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I didn't know they made them in sizes that small.

At the suggestion of an OEM, we used the big Heli-Coil inserts on stripped out holes on some heavy duty equipment at work. The equipment was essentially a big rotary crusher. We found that the Heli-Coil inserts actually lasted much longer than the original threaded holes in steel. It made no sense to any of us, but that's what the results consistently showed us.
 
When threading into aluminum, you should always use a coarse thread. Although 6-32 is the weakest tap and screw, it is the most durable thread. It is a good choice for tapping into aluminum. For bigger screws, use 10-24, not 10-32.
 
For the smaller tapped holes I find that using plastic washers under the screw head keeps the screw from backing out and doesn't require so much force to strip the threads.
 
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