What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

machine countersink

D

dspender

Well Known Member
I notice when I machine countersink some of the holes appear oval rather than round. Happens more often on thinner metal than thicker. Seems as though the guiding nubbin on the countersink bit holds steadier on thick stock than thinner. Any thoughts.
 
With the thinner stock, the CSK is removing material the entire depth of the hole thus you are actually enlarging the hole. When that happens the pilot on the CSK begins to wander and the result is an oval. The solution is to clamp some backing material (with a proper sized hole) to the backside of the hole being countersunk to give something for the pilot to ride in. This won't stop the hole from potentially being enlarged, but should keep it concentric if it does.
 
Wood under AL

If the AL is flat where you are countersinking, drill a thick piece of wood to receive the countersink drill guide and fasten the AL to the wood before countersinking. You can cleco the AL to your wood block to fasten it. The cleco does NOT have to go all the way through the wood. It will still hold the AL.

Some time ago I was having the same issue and wrote about it here:
http://airplane.athomeinthewilburness.com/2011/12/30/outboard-leading-edges/

... And I have a picture of the cleco-into-the-wood trick here:
http://airplane.athomeinthewilburness.com/2012/07/06/tank-attach-assembly/

Hope this helps.
 
Last edited:
I have found out that if your not using a high speed air drill to do the Machine countersink that the problem is apparent more often such as using an electric drill or not holding the drill perpendicular to the work.

Many times I would not go to the final depth at once but would go in steps with no issue,

Jack
 
I have only seen this once, but we had a #40 CS that had been machined wrong. It left the pilot sort of like an end mill, and it would cut a slot sideways in even thick material. That one got pitched...

Bob
 
I don't think mine does it all the time. When I really pay attention and try to keep the drill motionless, I don't see it. However I do notice if there is say a stiffener behind a flange and I am countersinking the flange, I don't see it. I think it is the pilot drifting while I am countersinking, especially on thinner material.
 
You must log in or register to reply here.
Back
Top