What does over dimpling look like?

[jcarne]

Those look nice and crisp to me!

[Mlidzct]

I cant seem to find an example of over dimpling. I keep reading over and over its hard/unlikeky to over dimple but in another thread I was discussing my results with a new set of dies and was wondering if under dimpling could be the cause. I went back over some holes and hit them pretty hard with a hardwood flooring hammer and the c-frame on the concrete floor. To me the dimples look crisp but from a distance the whole row looks rippled. I think it may be what the OP was trying to describe. Its very hard to capture the ripples on camera.


From distance:

https://drive.google.com/open?id=1td...eue_Macam1tR27

Closer shot:

https://drive.google.com/open?id=1KB...ExdjjTfQlH156v

Ripples when sighted at eye level:

https://drive.google.com/open?id=1oL...9Jk0JBolvXeQAh

[Mort04]

I did the same exact thing after reading the responses to my original post. I went over the holes again, the dimples looked the exact same, however once I riveted the skins on, those ?ripples? seemed to have went away, and the rivet lines look great to me. At least with my first time builder eyes...

[rv7charlie]

It's pretty hard to judge something like that when looking pics; you don't know the lighting, etc.

One thought: you do need to keep the skin perpendicular to the die axis when you strike the die with your hammer/mallet. That's probably the most likely way to mess up a dimple, assuming you're hitting it hard enough.

[Mlidzct]

Originally Posted by Mort04

I did the same exact thing after reading the responses to my original post. I went over the holes again, the dimples looked the exact same, however once I riveted the skins on, those ?ripples? seemed to have went away, and the rivet lines look great to me. At least with my first time builder eyes...

Thats interesting, the riveting process may have pulled the skin tight alleviating some of the rippling. Im a little hestitant to just try it but I may not have a choice. This is already my second hs skin on the right side. The first one had an unfortunate priming accident and was dented

[Mlidzct]

Originally Posted by rv7charlie

It's pretty hard to judge something like that when looking pics; you don't know the lighting, etc.

One thought: you do need to keep the skin perpendicular to the die axis when you strike the die with your hammer/mallet. That's probably the most likely way to mess up a dimple, assuming you're hitting it hard enough.

Originally they were done on drdt2 with support tables and all that. Setup/aligned good.

I rehit them on the c-frame on the floor. Supported the overhanging skin by wood blocks.

Either method same outcome with the ripples. The c-frame method left a bit more than a witness mark and is even a little galled from the impact

[rv7charlie]

What does it look like if you stand a high quality straightedge on the line of rivets?

I tried to do a little calculation on the force it would take to change the thickness of the metal. Here's the spec on 2024 T3:
http://asm.matweb.com/search/Specifi...ssnum=ma2024t3

Looks like yield strength is around 50,000 psi. I'm guessing the dimple die diameter is around 1/2". Area would be .25 squared, or .0625, times pi (3.14):~.1963 square inches.

.1963 * 50000 = 9817 lbs

If my numbers are correct, it looks like it would take close to 5 tons of force on the die to actually thin the metal.

Now, I'm not an engineer; maybe someone can check my work.

If they are correct, maybe someone can tell us how much force is generated by a medium swing of a 1 1/2--2 lb hammer.

Charlie

[deene]

To ask another question on this subject, has anyone tried to process under dimpled rivets after setting to smooth them?

[Mlidzct]

Originally Posted by rv7charlie

What does it look like if you stand a high quality straightedge on the line

The high points touching the straight edge are the dimples:

https://drive.google.com/open?id=1QH...9ocQZkfUG6fExd

[rv7charlie]

Again, hard to really tell anything for sure over the interwebs; what's the actual gap there? What size feeler gauge will slide into that gap? Experienced builders say my riveting is quite good, and I can see light intermittently along a riveted line. Pretty sure almost anyone will on their plane.

Can you scrounge up a couple of pieces of scrap, and run a line of rivets to joint them? Anything a few inches wide & 6-8 inches long would work for a test. Dimple on the floor with good hard whacks, like you did on that piece, rivet the scraps together, and then ask yourself how it looks. Might help you evaluate whether you're doing it right or not.

Also helpful is to get someone from your local EAA chapter to come over & look at it with you.