Spar Dimples

[mattputz]

Hi all - couple of questions about spar dimpling. First, I understand the best way to dimple for the driven rivets is to do the counter-sink in the underlying piece, then use the rivet head to create the dimple in the main web. Did you do the same thing with the flush screws? Just tighten the screw down such that it pulls the web into the counter-sink?

Second, were there any potholes associated with getting the counter-sink depth right? On the test piece I did, I counter-sunk a little deeper than I normally would have to allow for the extra material, but I'm just trying to figure out if there are indicators any of you discovered that told you your tolerances on that were getting out of range. Worried specifically about either trying to buck a flush rivet that's in a counter-sink too deep and ending up with it not being as tight as it should be, or on the other end just not having it counter-sunk deeply enough.

Thoughts?

Matt
Sonex #1585

[Bryan Cotton]

Matt,
I'm a big proponent of dimple dies and squeezers. They are the right tool for the job. Also to get the countersink depth right, do some trial runs in scrap. It should be deep enough that the dimpled sheetmetal is flush, but no deeper.

The purpose of the hobby is to buy tools.

[Sonex1517]

The purpose of the hobby is to buy tools.

I’ve taken to quoting this during my EAA Chapter build sessions. The kids love the phrase! (So do the adults!)

[racaldwell]

The financial cost of the project is pretty small compared to the time and labor commitment. Since I am not a professional (any of the aircraft building trades), my thinking is you should try to stack the odds in your favor the best you can to help ensure a good outcome. This definently includes using proper tools of good quality and the correct materials. Dimples and countersinks need the correct dies and countersinking cutters with microstops. How to squeeze the dimple dies depends on the application. Anything from rivet puller technique, hand squeezer, rivet gun set, C-frame, etc. all have their use in particular locations. The spar web would require the hand squeezer and possibly C-frame depending on what yokes you have for the hand squeezer.

Rick Caldwell
Xenos 0057

[bvolcko38]

Spot on Mr Cadwell!

[dbdevkc]

Dimples and countersinks need the correct dies and countersinking cutters with microstops.

Agreed - microstop countersink for adjusting to the exact depth and dimple dies for nice clean dimples with no tendency to crack. I think I did help the dimple for the screws by tapping the screw head with a dead blow.