Elongated countersinks

[rdamazio]

So far my countersinks have been pretty good, round and precise. I just started countersinking E-1007 on my -10 kit, and with the same technique got these results:



So I'm wondering - what's going wrong here? Why did this start happening only now, with so many previously-successful countersinks? Could it be that my tool (cage, bit or drill) needs replacement? Am I missing something obvious? (I do not have Parkinson's disease )

Also, I assume this part is now trash and I should order a new one? The holes look too large even for oops rivets (but on the other side, this part is sandwiched between two others - the hinge that holds the trim tab and the skin).

[Louavul]

Rod: I've gotten some wobble like this countersinking a piece that was .032 or less. The pilot starts to wobble as it enters "free space" beyond the thickness of the part. I now backup everything, less than .064, with a piece of scrap metal giving the pilot a seating area.

[rdamazio]

Originally Posted by Louavul

Rod: I've gotten some wobble like this countersinking a piece that was .032 or less. The pilot starts to wobble as it enters "free space" beyond the thickness of the part. I now backup everything, less than .064, with a piece of scrap metal giving the pilot a seating area.

Thanks, I shall try that!

Any thoughts on whether this part can be saved?

[John-G]

Rodrigo ?

Here are some helpful tips that will minimize the hole elongation while machine countersinking.

As Steve mentioned if the material is thin back it up with a piece of thicker metal ? preferably clecoed to an adjacent hole to the one you are countersinking to keep things from moving.

Use liquid Boelube on every hole to be countersunk place it on the pilot ad it will run onto the cutting surface. This will help in cutting the metal quickly and reduce the wear on the hole so it does not elongate as much.

Also, if using an air drill, turn the countersink bit as slow as possible (reasonable) - the less the bit spins in the hole the better. I placed an air valve at the end of the air hose and turn the air way down so the countersink bit can be made to turn slowly. I countersink using spirts of the trigger on the drill. Faster spinning bits can wander easier and chatter.

Happy building,

[N546RV]

Originally Posted by rdamazio

Thanks, I shall try that!

Any thoughts on whether this part can be saved?

I would definitely replace it. Don't let it get you down - my scrap collection contains an impressive variety of parts. Just part of the learning process!

[Brantel]

Yep, the pilot needs something to hold on to. Back it up with something to prevent it from walking.

[ERushing]

You might talk to Vans and ask them. They're going to be open shortly.

I had a similar issue and was advised that I could just fill the hole with JB Weld and try again... as long as there weren't a bunch of them. I had one that was pretty elongated like yours.

And, like the rest said, back it up with a thicker piece of aluminum and the problem should resolve. I just got a cheap piece of 1x1 angle aluminum from the Home Depot Aviation Aisle. It's now full of holes.

[rdamazio]

Had much better results today supporting the back thanks all for the hints!!



I was bummed that I'd have to wait for the replacement spar for the other side, but I guess now I have yet another reason to wait:



(this happened while countersinking the elevator trailing edge wedge - I guess adding the support behind it held it too firmly when at an angle, and it broke)

I just ordered another countersink bit (single-flute, this time) and boelube.

[John-G]

Rodrigo,

Countersink bits are hardened steel, and as such, they can be brittle so the pilot will not support much side loading ? as you have just experienced. When positioning the countersink cage, try getting squared to the hole and stay that way while countersinking. When done countersinking, release the downward pressure on the drill to allow the pilot to come out of the hole before removing the cage.

Also, after applying a drop or so of liquid Boelube to the countersink bit, I usually try to push straight down on the drill to compress the spring in the countersink cage while hand turning the drill chuck to make sure the pilot goes into the hole easily ? if all is well, hold the countersink cage and while pressing it downward (which will keep it firmly seated against the work surface) spin away with the drill and of course push the drill squarely towards the hole.

Your subsequent holes look much better so you are past the learning curve.

Happy building,

[rdamazio]

Originally Posted by John-G

Rodrigo,

Countersink bits are hardened steel, and as such, they can be brittle so the pilot will not support much side loading ? as you have just experienced. When positioning the countersink cage, try getting squared to the hole and stay that way while countersinking. When done countersinking, release the downward pressure on the drill to allow the pilot to come out of the hole before removing the cage.

Thanks, that's what I usually try to do, but in the case of the edge wedges there's an angle between the long hole and the surface to be countersunk (it specifically says to countersink perpendicular to the trailing edge face, not to the hole) - that's what caused the sideloading that broke it.