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Pneumatic dimpling technique

gotyoke

Well Known Member
Attached are pics of two dimples I made with the pneumatic squeezer for the Van's Lightbox kit.

It is my largely uninformed opinion that the dimple in pic #1 is better than the dimple in pic #2. I think the dimple in pic #2 is under dimpled. However, pic #3 shows the deformed aluminum resulting from pic #1.

So, which way should I go with this to make the best dimples with he least deformation?
 

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Are you using a Hans squeezer? Dimple them as hard as you can without hurting your hands, I don’t feel you can over dimple. If the part warpes, you can often flute it back straight. Here’s a dimple video from Cleaveland tool.

https://youtu.be/Qo9QCMaNSoA
 
Couple suggestions: 1) use the smallest yoke you have 2) set up the squeezer to completely close the dies (I actually go to mating and then about 1/4 turn interference). once you squeeze the part it'll completely dimple. you cannot over squeeze a dimple.
 
Also make sure that you hold the squeezer perpendicular to the metal that you are dumpling for minimum distortion.
 
Dittos on Norm's comment, but a good "rule of thumb" for judging dimple quality is to put a rivet in the dimple and see how it fits.

Way I was taught, the dimple "passed" when testing the fit of the rivet in the dimple, the junction between the rivet and skin would barely catch a fingernail dragged across the edge.

PS: The "slope" of the dimple should approach pretty much flat sided.
 
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A trick..

I've noticed that yokes tend to deflect at the end of the stroke. The larger C yoke deflects the most, resulting in an unbalanced dimple.

To mitigate this effect, I've taken to dimpling twice on thicker material, rotating the yoke about the hole axis 120 - 180 degrees or so from the first attempt.

The DRDT-2, C-Frame+Dead blow Hammer yields symmetrical dimples with a witness mark every time.
 
The EAA sheet metal class that everyone recommends on this forum says you can absolutely over dimple a hole. It was one of the biggest things I was doing wrong during the class appearantly. If you set the dies up in a hand squeezer, I think you would be surprised about how little effort it takes dimple thin sheets.

I like to adjust the hand dimpler to where the dies just bottom out and then another 1/4 to 1/2 turn. You don't need to squeeze hard, just until you start to feel resistance. For most thicknesses it's hard to tell where you go from just free squeezing the handles to actually dimpling the metal. Even on the drdt2, you go until you just start feeling solid resistance, there's no need to crank on these. You definitely don't need enough effort to come anywhere close to deflecting the yoke.
 
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The EAA sheet metal class that everyone recommends on this forum says you can absolutely over dimple a hole. It was one of the biggest things I was doing wrong during the class appearantly.

What do the teach is the result of over dimpling?

In all the years I have been doing this, I have never seen a case of messed up dimples that I would suspect it being squeezed or hit to hard.

I have seen many hundreds of cases where it was not dimpled hard enough.
 
What do the teach is the result of over dimpling?

In all the years I have been doing this, I have never seen a case of messed up dimples that I would suspect it being squeezed or hit to hard.

I have seen many hundreds of cases where it was not dimpled hard enough.

Stretched/oblong holes that result in the shop head not sitting around the entire diameter of the dimple, but allowing it to only grab half or 3/4 of the rim.
 
Stretched/oblong holes that result in the shop head not sitting around the entire diameter of the dimple, but allowing it to only grab half or 3/4 of the rim.

Hmmmm
I have never seen that and I have done tests to try and over do it.

Makes me wonder if it isn't more caused by excessive yoke flex which is a real issue.
 
That may be the case too. We did hand dimpling only during the class, and people putting all their effort into squeezing may have led to twisting and pulling and not keeping the dimple straight as well. Ever since I put maybe 5 lbs of pressure on the handle for 3/32 rivets and a little more for the #6 and #8 screw dimples, but I never strain to set a dimple. I haven't had any issues with rivet or screw heads not sitting flush up to this point.
 
Used small female dimple die

I appreciate all the answers, and my understanding of dimpling is a little less novice now.

I figured out my deformation issue. It was not caused by over-dimpling. It was caused by the female die being too big. When fully squeezed, the corner of the die pressed up against the wall near where it meets the flange. it was just barely, but it was enough for the metal to twist.

I switched to the small diameter female die and now all my dimples are great with very little deformation.
 
In my experience, ( two aircraft, minor work on a Bearcat and a wet wing project on a Sea Fury), I've never seen a pneumatic squeezer over-do a dimple.

The usual result is under forming, the dimple is a curve from the skin to the rivet hole. That the case, a rivet inserted in the dimple "stands proud".

Form it enough to witness a flat cone portion, rather than a velocity stack and you're in the ballpark.
 
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