OOPS! dimpled not machined

jim_geo · Post by **jim_geo** » Sat Nov 05, 2005 4:25 pm

I guess any question on this board is esoteric in it's nature. I just feel that this one really qualifies. I have managed; in a fit of jump ahead and git r done, to dimple the left elevator part #606PP top flange. That would be the trim tab rear elevator spar. The written plans state that this part is to be machine counter sunk on the top flange only. So my question is this. Is there any reason, other than that's not the way it's supposed to be done, that I cant machine counter sink the trim tab hinge instead? The only problem I see is that it will be harder to line the trailing edge of the tab up with the rest of the elevator since I will be resting the hinge on dimples while drilling it rather than a flat surface. I'm thinking if no one out there knows of some special circumstance I would machine counter sink a shim and use it for the initial line up of the hinge then discard that shim after lining up is finished.

captain_john · Post by **captain_john** » Sat Nov 05, 2005 6:02 pm

I don't see anything wrong with cs'ing the hinge. It is plenty thick enough.

As far as aligning the hinge, clamping it and drilling it with reasonable accuracy goes...

I would use the skin as a guide without the spar in place, so it doesn't wobble around like you explained. Maybe sandwiching it between the skin and spar just for drilling purposes would be best?

Depending on how much material is left after the countersinking procedure is done, you may want to back it up with a sheet of .020 perhaps?

Confirm all this stuff with someone much smarter than me before you do anything!

CJ

cjensen · Post by **cjensen** » Sat Nov 05, 2005 8:16 pm

i read an article recently that had to do with dimpling when c-sinking should have been used. it would work the metal a little more, but could you use the flush sets to flatten 'em back out?? that spar is fairly thick, but it would be work hardened somewhat.

Post by **Spike** » Sun Nov 06, 2005 7:52 am

Hmmm, Ive always run with the thought that dimpling is *always* better than C-sinking if the assembly will still fit. Dimpling leaves more material for more strength, and the flip side is that C-sinking is potentially risky.

mustang · Post by **mustang** » Mon Nov 07, 2005 1:04 am

Well, you are right to think of the alignment problems arising from the pre-dimpling. I had problems with the hinge alignment without the dimpling. It seems difficult to get it all clamped together and still laying on a flat surface to get the trim tab trailing edge aligned with the rest of the elevator. I blew it the first go-around and threw the hinge out and bought another one, starting fresh. The second one worked out OK.

Cheers, Pete