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How to dimple for #12 bolt?

M

mg1003

Member
Two days ago I got stuck installing the counterweights into the rudder. The instructions call for the #10 bolt to be countersunk. I looked through my tool kit, found no #10 dimple die, ordered one (waiting for them to arrive).

Today, I am looking at the instructions for the elevator. Here, there are four #12 bolts to be countersunk. I cannot find any #12 dimple dies for sale. How do you dimple the counterweight skin for these bolts??
 
something in the instructions

I don't have the written instructions in front of me, but I sort of remember something in them to tell you how to do it. You should check, but I sort of recall that you countersink the lead with a regular countersink, then as you tighten the flat-head bolt, it pulls the aluminum into the countersink area and forms it. Just tighten it until the head is flush. You could dimple it for #10 first to get it started, then let the bolt head form the rest.

Good luck
 
I assume that the bolts go through a piece of aluminum that needs to be dimpled and the counterweight. To dimple the piece of aluminum, simply match drill the aluminum piece to the counterweight, countersink the counterweight, then screw the bolt through the undimpled piece and the countersunk counterweight. The aluminum is dimpled by the bolt, with the counterweight as the dimple die.

Tracy.
 
You guys are great! It makes perfect sense to use the bolt to create the countersink. I will report back how it works out.
 
Both the aluminum and the lead are soft enough to self-form under bolt pressure, it's quite easy.
 
Counterweights

mg1003 said:
Two days ago I got stuck installing the counterweights into the rudder. The instructions call for the #10 bolt to be countersunk. I looked through my tool kit, found no #10 dimple die, ordered one (waiting for them to arrive).

Today, I am looking at the instructions for the elevator. Here, there are four #12 bolts to be countersunk. I cannot find any #12 dimple dies for sale. How do you dimple the counterweight skin for these bolts??
Click to expand...
Are you sure that you're reading that correctly? I don't recall any bolts being dimpled, they are countersunk. I think, as I recall, you drill a recess into the lead weights to accept the bolt head, and washer/nut on the inside weight on the elevator. On the rudder you do the same. I'll check my plans Friday to make sure. Countersinking and dimpling are two different things.
Mike H 9A/8A
 
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mg1003 said:
Here, there are four #12 bolts to be countersunk.
Click to expand...
Are you sure those aren't #10s not 12s? My 8 elevators (I think 7s use the same ones) have #10 flush screws holding the counterweights in place. Never heard of a #12 bolt anywhere on an RV.

Don't confuse the bolt/ screw size and the drill size. #10 screws are the same size as AN3 bolts (3/16) and the proper drill size for their holes is a #12 drill.
 
#10 CS screws

The -9 has #10 CS screws. I bought a tool kit that had the #12 dimple die with it and I used my hand squeeze (before I got a pneumatic squeeze) to make the dimples. I used one of my CS cutters to remove some of the lead for a flush fit on the inside. The dimples were not as good as I hoped they'd be because my dimples were a hair short of making the crew head sit flush, but, now that it's all assembled no one will ever no but me....... and everyone that reads this thread.

The dimpling is only necessary because of the countersunk screws. There are two ribs at the top of the rudder in the counterweight location. Both ribs have the flange facing out which provides an extra gap between the fiberglass on top (not needed) and the VS below. Probably could have gone with regular hex head bolts and it wouldn't have made any difference - possibly a tiny bit more weight.

I agree with danielhv, just get the #12 dimple die.
 
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sprucemoose said:
Are you sure those aren't #10s not 12s? My 8 elevators (I think 7s use the same ones) have #10 flush screws holding the counterweights in place. Never heard of a #12 bolt anywhere on an RV.

Don't confuse the bolt/ screw size and the drill size. #10 screws are the same size as AN3 bolts (3/16) and the proper drill size for their holes is a #12 drill.
Click to expand...

You are correct there is no such beast as a #12 bolt however a correctly used #12 reamer will make a 0.1890" diameter hole for an AN3 (3/16) bolt of diameter range 0.186 to 0.189 - which has a #10-32 UNF-3A thread.

But enough of being a Smart Alec - I'm sure you do get dimple dies for 3/16 flat head bolts and screws.

Jim Sharkey
 
... just to close this story.
Indeed, the fasteners for the elevator counterweight are #10 (while the hole is #12). So there is no need for a #12 dimple die. I did buy a #10 dimple die and used it on the rudder counterweight and it worked quite well (and it should work equally well for the elevator). I am disappointed that the #10 die was not part of my tool kit.
 
and the right answer is to dimple first

I tried the other method - countersink the lead, and draw the AN509 structural screw to form the dimple.

To completely form the dimple, I had to exceed the torque spec. of 20-25 in-lb. Removed and replaced the two AN509 screws and nyloks, set to proper torque now.

It's pretty neat that this reference has persisted this long, to be updated.
Thanks Doug.
 
Build your own dimpler--

I used a counter sink and drilled into a piece of oak. Then I set the rib (RV8 rudder top rib) over the oak, inserted a #10 screw and gave it a few hits with a flush rivet set in my gun. Worked perfectly. No need to buy a #10 dimple die for the few parts on the rudder and elevators--may need one for more parts later on. This was not my original idea--found it in someone's log. :D

Skyking902001
RV8, emp.
 
I countersunk the lead weight , then dimpled the aluminum with #10 dimple set, and then thrrew in the #12 screw....worked out well and the #12 screw sets nicely...
 
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