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Mysterious serrated holes after dimpling

FL-flyer

FL-flyer

Member
Mysterious serrated rim after dimpling

I have a question regarding dimpling. I am seeing a very odd looking serrated rim on the pointed side of the dimpled hole after dimpling and I don't know if this is something that I have caused or is just a result of normal dimpling.

Here was my process:
For match drilling the 3/32 holes I used a #40 new drill bit from pan american and deburred both sides with a dog leg speed deburr tool.

For dimpling the holes, I am using Cleveland's 426-3 spring back dies with a DRDT2 dimpler. I did follow the directions with the DRDT to make sure the ram was adjusted correctly.

I have attached some photos and I tried as best I can to capture the issue. Thanks in advance for your assistance.
Casey


https://www.flickr.com/photos/153747629@N08/33869053351/in/shares-69f344/
 
Last edited by a moderator:
The serrated rim is something that happens through the dimpling process. I had the same thing happen when I manually dimpled with a "C" frame and dead blow hammer.
 
Thanks Robert! Glad to hear that. Is there anyway to avoid this? Perhaps I can deburr again after dimpling to try to remove these.
 
Just me

What I do is run a scotchbrite pad or fine sandpaper over the dimples after dimpling. This gets rid of any rough edges before riveting, because no matter how careful I deburr, sometimes the holes will come out feeling rough after dimpling. JMHO.
 
You might be over deburring, thinning the edge. Try taking a piece of scrap and lightly sand the back side of the hole, dimple, and see if that looks different.
If it does, change your deburring technique. One turn with a fluted deburr tool is all it takes if that. The style of deburring tool you are using takes off meat fast. You are only trying to break the edge, not put a big chamfer on it.
 
I think you might be on to something. It turns out that I was deburring the heck out the skins (more like countersinking!) Tried again with minimal deburing and it came out perfect! Thanks for solving my issue! Although now after dimpling, the pointed side of the dimpled holes feel very rough. I wonder if I need to deburr this side again (or sand) to make it smooth or is this normal?
 
FL-flyer said:
I think you might be on to something. It turns out that I was deburring the heck out the skins (more like countersinking!) Tried again with minimal deburing and it came out perfect! Thanks for solving my issue! Although now after dimpling, the pointed side of the dimpled holes feel very rough. I wonder if I need to deburr this side again (or sand) to make it smooth or is this normal?
Click to expand...

Normal. I am traveling but will try to find a picture of how the dimples nest. You're feeling the edge of the sheet. You should be good now.
 
Best to start with a sharp drill. Leaves less of a "burr" when the drill punches through.

Whether flat or dimpled, you want to debur the minimum amount possible, retaining as much of the "cylinder" walls again, as is possible.

Be careful about leaving stress risers, the hole is stretched further when the rivet swells in diameter from setting.

Though it makes my finger tips sore, I don't use a handled tool for rivet holes, I twirl a drill by hand.

Inspect your holes under magnification and
Maybe do some test riveting then cut through and inspect.
 
It happens.

When you de burr you only want to just go lightly around one or two turns, just enough to take the sharp edge off. The upper shoulder of the cone area will take the shear forces of the joined stack-up once it is riveted together. Sometimes you don't get a perfect hole. It will get better as you get more practice, there are only about 15,000 rivets in a two seat RV. Keep up the good work. Art take time, it will be worth it some day.
Hope this helps, Yours, R.E.A. III #80888
 
Check out the DRDT-2 RIVET DIMPLER, or the R2D2 as I refer to it. Much easier on the ears and arms than pounding with a C frame.

Ed
 
Thanks Ed, yes, I have the R2D2 dimpler and love it! The issue was that I was deburring too aggressively. One of our EAA members came to my house last night and said i am not allowed to use a speed dimpler anymore, haha. So now I have to use only an over sized drill bit twirling it between my fingers. Probably a good thing...

Thanks to everyone for your help with this issue, I really appreciate it!

I do have one additional question, does anyone know how to deburr the inside of an aileron rib (the holes near the trailing edge have very little clearance on the inside and can't get the bit in there.

Thanks!
 
Also, a reamer will leave more of a round and clean hole than a twist bit when match drill-reaming :D
 
FL-flyer said:
I do have one additional question, does anyone know how to deburr the inside of an aileron rib (the holes near the trailing edge have very little clearance on the inside and can't get the bit in there.

Thanks!
Click to expand...

Just hit the back side of the hole gently with some 350-400 grit sandpaper.
 
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