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How big is too big?

missile29

Member
Just dimpled RV-10 rudder skins. I understand that dimpling the holes in the skin will enlarge the original hole a little, but how big is too big?

MIL-R-47196A table 1 gives the max hole diameter for a 3/32” standard rivet as 0.103” but after dimpling (C-Frame and pneumatic squeezer both) I’m measuring 0.110” or more. Measurement is admittedly made crudely with calipers, but it’s definitely well over the 0.103” - regardless of tool used to dimple. Holes were final drilled with #40 reamer, and minimally/carefully deburred.

So, is the 0.103” max spec reasonable and applicable to dimpled holes, or is it only for a “standard” (universal?) rivet?

If <= 0.103” is not really required for a dimpled hole, what is? Has anyone else measured what they normally get after dimpling?

Is it possible to “over dimple” and if so, would it cause the holes to be too big? (Seems to me that the geometry of the dies would not necessarily have a tendency to enlarge the hole.)

Am I totally overthinking this here? Should I just follow the plans and put the calipers away?

Thanks!
 
Probably overthinking this. As long as you use the correct size dimple die from a reputable supplier you will be fine. For a size 3/32 rivet the dimple die should say either 3/32 or #40.
 
Just dimpled RV-10 rudder skins. I understand that dimpling the holes in the skin will enlarge the original hole a little, but how big is too big?

MIL-R-47196A table 1 gives the max hole diameter for a 3/32” standard rivet as 0.103” but after dimpling (C-Frame and pneumatic squeezer both) I’m measuring 0.110” or more. Measurement is admittedly made crudely with calipers, but it’s definitely well over the 0.103” - regardless of tool used to dimple. Holes were final drilled with #40 reamer, and minimally/carefully deburred.

So, is the 0.103” max spec reasonable and applicable to dimpled holes, or is it only for a “standard” (universal?) rivet?

If <= 0.103” is not really required for a dimpled hole, what is? Has anyone else measured what they normally get after dimpling?

Is it possible to “over dimple” and if so, would it cause the holes to be too big? (Seems to me that the geometry of the dies would not necessarily have a tendency to enlarge the hole.)

Am I totally overthinking this here? Should I just follow the plans and put the calipers away?
Thanks!

Use a #41 drill bit.
 
Last edited:
...Should I just follow the plans and put the calipers away?

Yes...

But - Spend the money on a great set of tools and become familiar how they work.

Make sure the runout (the amount of wobble in the drill chuck) is as small as possible. Excessive runout will cause holes to be larger and "tri-lobed". If you can feel the drill vibrate in your hand, it's too much.

Rule of thumb:
#41 or #40 drill for AD3-n rivets (3/32")
#31 or #30 drill for AD4-n rivets (1/8")
and so on...

Have fun!
 
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