SonexBuilders.net

Hi ,
I'm having a hard time getting the countersink right for the 3/16 machine screws.
Plan says countersink using 100 degree bit to 27/64". But the skin doesn't sit flush after tightening the screw , it actually pulls the skin in and causes the edge of the skin to rise up,and if I don't countersink as deep it would leave gap under the skin. I am wondering if100 degree is correct ?
Thanks
Ben Abachi

The 100 degree angle is the correct angle. We found the dimple set to be the issue when we could not get a good fit. We bought a good set and made our layers sit a lot better.

I'm using the machine screw to dimple the top skin . What kind of dimple set did you use ?
Thanks

I use a regular 100 degree dimple die for the screw I'm using. To set the countersink I'll dimple some scrap and use it to set the microstop on another piece of scrap.

Hi Bryan,
I think ,my problem could be that I'm using the screw to dimple the skin,and that's making the diameter of the dimple too large.
Did you get yours perfectly flush ?
Time to call my RV friend,and see if he has the 3/16" 100 degree dimple die.
Thanks

Just remembered,you bought yours pre assembled .

I was not able to get the screw to work very good for me. We bought cleaveland tool spring back dimple die set. You can buy them from cleaveland or skygeek I believe. Might be overkill, but it makes a very nice dimple.

http://www.cleavelandtool.com/custompag ... -dies.html

We tried some cheaper version and it did not do as nice as the spring back version.

Mike

I couldn't recall how I did the dimpling, so I just checked back in my build log. I found this entry:

Received delivery of countersink microstop, a 5/32 cutter, a 3/16″ cutter, and a 5/32″ spring back dimple die. Spent some time test drilling countersinks with the 5/32″ cutter into scrap .125 material and dimpling scrap .032 material. Used the borrowed Avery C-Frame for dimpling – very nice!

Now if I remember correctly, I used the screw itself to dimple the 3/16" hole in the web material. You stated:

But the skin doesn't sit flush after tightening the screw , it actually pulls the skin in and causes the edge of the skin to rise up,and if I don't countersink as deep it would leave gap under the skin.

That seems like the dimple just isn't deep enough. Wondering how you set that dimple. If you cleco and clamp the sandwich together and put the screw in place - what would happen if you tapped it in with a rubber mallet - would it finish setting the dimple? I mean doing that as opposed to putting the nut on and torquing, causing the dimpled web material to bend up as you say, as you tighten the nut and pull the dimple down into the countersinked material.

I also found this note in my log:

Fitting of the dimpled main spar web onto the web stack and spar cap (with clecos). Noted some bending of the .032 main web that took place during the dimpling process. Took the spar apart to remove the bending with the hand seamer.