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Deviant behavior...

bjdecker

Well Known Member
Ambassador
I generally follow "The Rules", or stay inside "the Box" as my wife likes to say. However, after a particularly bad experience with countersinking some holes, I decided to attempt dimpling instead.

The setup: See page 9-10 of the RV-14 Empennage plans if you'd like to follow along. The plans call out for countersinking the top flange of the rear spar (E-00907-1L) along the section where the trim tab hinge mounts.

Situation:
My handy-dandy-good-for-drilling-wood-only-Dewalt drill motor has excessive run-out; I know this, but I proceeded using it along with the micro-stop countersink cage and created a bunch of **** "snow-men" countersunk holes in the rear spar. Into the recycle bin with ya...but wait...

Idea:
More deviation from plans -- Van's supplies MS20257 hinge, which I do not like - especially for flight surfaces, so I had ordered MS20001 to use for the trim tab attach.

Instead of countersinking the replacement spar in the aforementioned area, I am going to dimple it, and dimple the underlying hinge material. The test I did on the buggered up rear spar and scrap hinge seemed to work well. Dimpling the hinge material requires a little "ooomph" but easily accomplished with C-Frame or DRDT-2 or Pneumatic Squeezer.

Aside from the "difficulty" in dimpling this hinge material (it's .056" for the MS20001 and .040" for the MS20257), anyone see a reason dimpling this stack up is a bad/unsafe idea?
 
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I just did a trim tab with dimpled hinge (P3) because I didn't like countersinking the thin spar material. I think it came out great, but that's just me. I have been told dimpling distorts the hinge but I didn't have that problem.

Not advising you to follow my plan but I'm happy with the results.
 
Brown Tool is selling an excellent Sioux drill now for a good price. That and an inexpensive air system will really pay off in the long run. I love the precision and effortless way my Sioux drill does the job..... I only use the battery powered drill for drilling out rivets, turning screws, coarse work in general.

It really is worth it to buy good tools. It makes the work better, more fun, with less rejected QA.

For my second build I bought a keyless chuck - that was also something I wish I had gotten a lot sooner. Pretty cool how the chuck is changed on these drills....
 
Two way tape an aluminum backer to the thin material you plan to countersink. This will give you a deeper pilot hole for the countersink pilot to follow, giving you nice clean countersinks!
 
Two way tape an aluminum backer to the thin material you plan to countersink. This will give you a deeper pilot hole for the countersink pilot to follow, giving you nice clean countersinks. I use high quality double sided carpet tape. A little heat with a hairdryer make's separation easier.
 
And some here use a rivet fan; cleco a few holes and then the steel fan guides for the rest. Works well on a long length of hinge or other material with 3+ holes.
 
My soiux drill will make snowmen on thin material, probably not run-out. Use a backer to support the pilot, if you still have the scrap piece try it.
 
Thanks!

I love this place -- great advice is always to be found.

1. I did use the hinge material as the "backer" for the countersink pilot as directed by the plans. The mistake was not using enough clecos -- too much space and movement in the backer material. I'll use the rivet fan + cleco every other hole next time!

2. Brown Tool has a lot of my money now :) I have one of each RPM drills that Sioux has, and I won't use anything else...The Dewalt was a convenience thing; stupid in hindsight.
 
I just did a trim tab with dimpled hinge (P3) because I didn't like countersinking the thin spar material. I think it came out great, but that's just me. I have been told dimpling distorts the hinge but I didn't have that problem.

Not advising you to follow my plan but I'm happy with the results.

I had done this in the past and sure enough distort the hinge and I noticed it when I put the whole thing together. I had to drill it out and rebuild. It may not have been issue for short duration but I suspect in a long run, I would have had problems.
 
I had done this in the past and sure enough distort the hinge and I noticed it when I put the whole thing together. I had to drill it out and rebuild. It may not have been issue for short duration but I suspect in a long run, I would have had problems.

I'm happy with result in my case:
 

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I'm happy with result in my case:

I wasn’t happy with the micro click machine countersinking on the hinge. I used the ole Cleveland main squeeze with spring back dies to dimple the hinge on my vans toolbox. I got results like yours and I’m quite pleased. I will use said process on our 14.
 
Results...

Good morning;

I finished the elevator and trim tab and can report that dimpling the hinge material & rear spar worked out great. The MS20001 hinge is tighter and there is no side-to-side slop or rattle in the trim tab.

I do have a couple of findings that are worth mentioning:

1. MS20001 is a little thicker than MS20257 and will twist and bend when dimpled; more than the '257. However, it will fall into place when cleco'd and riveted
2. The distance from center of the hinge pin to aft edge of -P2 is not the same as -P3; if you use -P3 you will need to adjust the pilot hole location, else the trim tab will NOT line up with the elevator trailing edge.
3. I further dressed the dimpled holes in the hinge material with a single hole deburring tool - this allowed the dimples in the elevator to "nest" a little better. There's .056" worth of material, so shaving off .001" isn't a factor.

On to the next project!
 
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