S

Spindrift

Well Known Member
I'm about to install my AFS AOA in my wings, but need to dimple the #4 screw holes. Any recommendations on how to accomplish this in a finished wing? Should I dimple for a 3/32 rivet, then machine it a bit until the screw is flush? I've experimented on some scrap, but before I drill the complete QB wing, I thought it was worth asking (and a search didn't turn up anything).

Thanks,
 
#4 dimple die not needed. Here's how to do it:

The head dimensions of a standard #4-40 screw (MS24693) and a standard 1/8" flush solid rivet (AN426AD4) are practically identical. So drill #34, then use a set of dimple dies (the kind used with a pop rivet puller) meant for an AN426AD4 rivet, which you probably already have:
http://www.wicksaircraft.com/catalog/product_detail.php/pid=1585~subid=9031/index.html

Easy, no exotic/expensive tools, and perfect results.

Here's an excerpt from a detailed writeup I did on installing the AoA ports:

The pressure ports are each implemented with a piece of machined delrin that attaches to the inside of the skin with two countersunk #4-40 screws and nuts (and will be pressure sealed with a gasketing material on final installation). Note that the #4-40 screws provided with the kit don't appear to be standard mil-spec hardware, and I'm uncertain of their exact countersink angle. I replaced them with MS24693-S8 screws that have a 100? countersink angle, and conveniently very close to the same head dimensions as an 1/8 inch diameter AN426 rivet. Still, the diameter of a #4-40 screw shank is considerably smaller than 1/8 inch, but that's no problem. I found a good way to drill and dimple the wing skin for these screws. Drill the holes to #34. A #4-40 screw will just barely slip through that hole, and so the delrin part can be screwed into the first hole and then used as a guide for precisely positioning the second hole. After both holes are drilled, they are dimpled using a pair of dimple dies that are pulled with a pop-rivet puller tool (not to be confused with 120? pop rivet dimple dies, these are 100? dimple dies meant for solid 1/8" rivets). These 1/8" solid rivet 100? dimple dies are available for about $10 from Wicks. The nails that are provided with the dimple dies for use as a puller shank are actually quite smaller than 1/8" and fit easily through a #34 hole. The dimpling process enlarges the hole slightly so a #4-40 screw now slides through it easily, and the dimples fit the MS screw heads quite nicely.​

You can read the full writeup here:

http://www.kalinskyconsulting.com/rvproj/aoa.htm
 
A squeezer-type dimple die set won't work here

I'm sure the Cleveland dimple die set is an excellent product, but it won't work in this case. Bill indicated that he has QB wings, so the skin is already on. If using the recommended locations for the AoA pressure ports, a squeezer yoke won't be able to reach deep enough from the edge of the wing. Hence the need for the puller-type dimple dies.
 
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