Dimpling question...

[JDanno]

This is a "noob" question but after checking the archives to no avail I decided to see what y'all have done.
I just ordered the RV-10 tail feathers and while I'm waiting for them to arrive I decided to practice on the tool box kit.
I bought the Avery dimpler/riveter with the 22" throat and mounted it on my bench. It works really well except that it leaves a round imprint around the dimpled hole. It isn't a depression, just mars the metal a bit. I've tried hitting the dimpler with less force, softer more easier, etc. Can you dimple thru the plastic covering?
Any suggestions on how to avoid this?

[airguy]

This is called a "witness ring" and simply shows that the flats of the dimple die have contacted the sheet metal, indicating full formation of the dimple. It's normal, and you actually WANT to see that mark because it tells you that the dimple dies have completely done their job. Up until the point where the flats make contact, the dimple is still forming - and if you back off the depth of the dimple stroke on a DRDT-2 style dimpler, or simply hit it with less force with a hammer-style dimpler, you won't know if you're 60% done or 98% done without a witness ring. When you see the ring, you know you're 100% done. The last step in the process of building will have you scuffing that anyway and painting over it, so no issues there.

Some builders dimple through the plastic, I found less than desirable results that way, I strip the plastic off as most other builders do.

Once the flats make contact, no more metal movement will occur - you are not damaging the sheet metal or the tool by creating the witness ring.

[mgomez]

If you decide to polish your airplane, those circles can be removed readily. If you paint it, they won't be visible. I saw them too, and since I intend to polish my airplane, I made a few deliberate circles on a piece of scrap and polished them off in seconds.

[TerryWighs]

I recommend you do NOT dimple without removing blue film....Okay to drill through but remove just enough of a strip to deburr....then dimple. Often small shavings of aluminum are hidden/sandwiched between the flim and skin surface.

[mgomez]

Originally Posted by TerryWighs

I recommend you do NOT dimple without removing blue film....Okay to drill through but remove just enough of a strip to deburr....then dimple. Often small shavings of aluminum are hidden/sandwiched between the flim and skin surface.

I agree. Drilling through the blue film is fine, but I remove it before deburring or dimpling. Or riveting

[mcencula]

Depending on the severity of the ring, it's possible that the dies are bad. I was recently helping my brother work on his RV-6A and we found that the dies he had left a ring deep enough you could feel it...not just see it. After talking to the vendor (not Avery), they were replaced.

I don't know if this is the same as your situation, but though I'd pass it along in case the info is useful to you.

Good luck and have fun!