Newbie riveting and dimpling questions...

DCat22 · #1 09-30-2010, 11:11 AM

Newbie riveting and dimpling questions... otherwise, all makes sense, and I actually like deburring.

So, starting on my training kit and I had a few questions that I wasn't quite sure the answer to from reading around. No pics yet, but I can grab then tonight.

1. What is the best approach when putting a flush rivet through a dimpled thin skin and then into a countersunk thick piece (like an angle).

In the Vans material, and elsewhere here is "Drop a rivet in place on the flush material and then when it is flush with the dimpled surface go about another .005. Vans says "a few clicks" on the countersink."

When doing this last night...the dimple was still pretty far above sitting flat in the angle, with about a 0.020 gap in the metal next to it. I had to countersink (as an experiment) quite deeply to get the dimple to fully sit in the countersink. I'll have to look again, but I'm pretty sure this was about to the point of enlarging the hole in the angle.

Does this sound really wrong? If so, I'll get a step by step picture set of what I'm doing so its more clear..

2. What is the best way to handle a dimple that should not have been? (ie. if you dimpled the spot for a standard non-flush rivet by mistake.)

I did this on purpose to see what would happen...and then flattened out the dimpled area between two pieces of flat/polished steel in a vice. Seemed to work OK. But what is the proper method?

Thanks much!

Thermos · #2 09-30-2010, 11:51 AM

Rick,

I had the same experience as you when I first experimented with Vans' instructions for countersinking...when done to their procedures, dimpled skin didn't seem to fit. I called tech support, Scott Risan said that the dimple will conform somewhat to the countersink when you squeeze/buck a rivet into the hole.

So I pressed on according to the directions and haven't really had a problem since...tail, wings and now fuselage. The plans procedures seem to work ok.

My $0.02...

Dave

airguy · #3 09-30-2010, 12:30 PM

Yep. Rivet a few of them before you decide the countersinking procedure is wrong, then adjust from those results.

DCat22 · #4 09-30-2010, 01:00 PM

Thanks.

Bullseye · #5 09-30-2010, 08:37 PM

Yeah, I can attest that trying to countersink too much to make things sit nicely before riveting is not the best way to go.

I enlarged a few of my rudder trailing edge angle countersinks that way, but pushed on.

Luckily (unluckily?) I dropped my rudder, so I get to redo it the right way now.

Great advice from everyone. Thanks from me, too.

terrye · #6 10-01-2010, 06:03 PM

Typical engineer, I did some drawing layouts and calculations to find out just how big the countersink hole in the mating part had to be. The problem is deciding just where the inside radius is on the dimpled part and how it nests into the countersunk part. As a result, you end up with a range depending on what assumption you make. And then to set your microcountersink, you have to measure the diameter of the conical countersunk hole. Not easy. I used the points on my digital calipers.
Here's a table I made, T is the thickness of the dimpled skin, D is the range of diameters of the countersink hole. Lower end of the range assumes no radius on the inside of the dimpled skin (not actually true if you look at the dimple dies).

Rivet---T----D
-3----.020---.194-.208
------.030---.200-.223
------.040---.208-.230

-4----.020---.240-.254
------.030---.247-.269
------.040---.254-.283

aturner · #7 10-02-2010, 07:42 AM

Terry, this is a very useful table, thanks. Unfortunately for me, I just finished the marathon countersinking on the fuselage, had to determine depth via trial and error, and initially went too shallow. I suspect I'm not the only one to do so.

wrongway john · #8 10-03-2010, 08:10 AM

Very thankful for everyone?s advice on this thread; info will come in handy since I?m fixin? to experience my first countersinking.

rv7charlie · #9 10-03-2010, 12:10 PM

I'd suggest playing with dimpling technique. If you under-dimple, it will affect the way the dimple sits in the countersunk hole (implied in earlier posts). It will also affect the appearance of your finished joint.

Try dimpling the skin with a 'heavy hand' on the mallet, then test the fit, and also, drive the rivet & compare the finished surface with a riveted joint that has a lightly-hit dimple.

Charlie