Making coil shells - adjustable wings

[Charles (Upstate NY)]

The width of the lower rod where the coil attaches varies by model and brand of detector. So how do you make a single coil shell mold that fits multiple lower rod widths? Here's my solution...

These wings are machined/polished 1/4 inch 6061 aluminum with six holes drilled and tapped (6/32) in the bottom. To vary the width of the wings to fit different sized lower rods, a staggered pattern is drilled into the coil shell mold as shown in the 3rd pic below. This particular pattern fits lower rods of .900, .750, and .720 inches wide. Note that regardless of which pattern is selected either none or very little of the other holes are exposed, certainly not enough to effect vacuum forming with .060 ABS.

I decided the wings had to be drilled "after" they were machined because the screw hole location is critical. If I predrilled all the holes and was off even a little when I flipped the stock flat to machine the wings, the error would be cumulative. Therefore I had to machine a jig to hold each wing in the vise for drilling as a final step. I'll post a pic of the jig if anyone is interested. Mostly I just thought I would get this new forum started with a post! :-)

[DarthCarl]

Charles, I was thinking of you when I created this forum. I need to move your vacuum machine threads over, but I noticed that a lot of the pic links are now dead. If you can send me those pics, I'll drop them in the local upload directory and fix the links.

This looks like you're back to vacuum-forming the wings. I thought you had switched to casting rosin, and gluing it on the shell.

And yes, I'd like to see a pic of the jig.

- Carl

[Charles (Upstate NY)]

Thanks! What do you think about moving this forum up to the Technology group instead of down here under misl for improved visibility? I didn't even spot it until perhaps my 4th visit.

I'll repost the vacuum forming stuff with better pics and more info in the near future. I routinely delete older pics from my website host but I'll save the pics for this stuff going forward.

I felt the issues outweighed the benefits of cast wings verses vacuum formed wings. The two big issues were weight and bonding. The external wings need a base of at least .200 and that is needless weight. The big issue was trying to bond two disimilar plastics (ABS and Urethane), both chemists I spoke with said there is no such cement, one can obtain a good bond with various products but none are failure proof and even at that one must roughen both surfaces and take extra care when bonding.

Then you have to think about the stress on that bonded joint, large coil flexing tiny wings. The strongest joint would be to pour the wings inside the shell when potting the coil, that way the wings become an integeral part of the coil with zero added weight.

So the challenge then became overcoming the issues specific to vacuum formed wings but that is the topic of another future post. I love the new forum software, I'm thinking of using vbulletin for my site as well.