Mastering the Counter-sink

[RVG8tor]

OK, I did a quick search but did not find anything that helped me so I am asking here. I am doing a training project and counter sinking the thick spar piece is touch and go. Some come out nice and smooth and some are chattered. I can't figure out what I am doing wrong. I would appreciate some pointers, drill speed, pressure used etc. I am using the counter sink cage I bought with the tool kit. I have also taken a class doing the same kind of project but don't recall having issues with the counter-sink in the class. For the life of me I can't get a consistently smooth counter-sink. Thank you in advance for any help.

Cheers

[pmccoy]

Looking back on the practice kit... my results were... less then good...

1000 hours and a year and half later... when it's time for me to countersink, two things have to happen.

First - the lead on the countersink bit must be going into something. If you are holding the cage in your hand, try pre-drilling into a piece of wood. This will give the countersink lead a place to hold a true line.

Second - rig up the drill press. I find it much easier to keep the bit centered when using the drill press. I still use the countersink cage to set the depth, and I have a piece of wood under the part, so the lead bit can have something to drive into. That helps to keep it turning straight. Hope this helps. Just keep trying, you will come up with better results.

It always seems like the second part looks better then the first

[FlyerJumper]

One other thing... try slowing the drill speed down. For drilling in aluminum the speed needs to be pretty fast. But for countersinking, it's quite a bit slower.

Good luck!

[jim]

Use a handheld electric or cordless drill and slow it down. Drill press is good except you won't easily do that on wing spars. Sneak up on the depth, make sure chips are cleared from the cage after each, or at least, every other hole, chips on the face of the cage will affect your depth on the next hole. Practice before you do it on a good piece. Some type of backing with a pilot hole helps.

Good luck,

jim

[mike newall]

And why is it that when you set it up for a rivet session, put it back on the rack and come back a week later, it needs readjusting - them tool Gremlins again

[Baseball Dad]

Originally Posted by pmccoy

First - the lead on the countersink bit must be going into something. If you are holding the cage in your hand, try pre-drilling into a piece of wood. This will give the countersink lead a place to hold a true line.

It took me a while to find this out myself. It's one of those things that I don't remember being told before. This is especially critical on thinner stock. No matter how new or how well you've taken care of your countersink there will be some wobble. The backup piece of wood will hold everything still so that you don't wallow out the hole.

[gpiney]

I use a cordless drill. I run it so slowly I can count the RPM's. I may go after the same hole 2-3 times, checking depth with a rivet each time. I found I may have to adjust the cage 1-2 times in a series to keep things correct. Patience (something I rarely posess) is the key.

[flybill7]

Originally Posted by Baseball Dad

It took me a while to find this out myself. It's one of those things that I don't remember being told before. This is especially critical on thinner stock. No matter how new or how well you've taken care of your countersink there will be some wobble. The backup piece of wood will hold everything still so that you don't wallow out the hole.

I concur; this is the key to smooth countersinks. In addition to a backup piece of wood, I made a little piece of angle an inch long with #30 and #40 holes in it. I use this angle to provide backing for stuff I can't lay flat on a piece of wood.