Countersink problem

C

CDH

Joined
Jun 8, 2007
Messages
283
It should be so simple...buy the countersink bit from a knife supply house (Jantz, TKS, etc.) and it should cut nice and clean, right!?!?!?

PB020002.jpg


Yeah, right. About half of the holes are this bad. This is well seasoned (2+ years) mesquite wood and this bit had drilled/sunk maybe 50 holes...and it is cut from a standard cobalt drill bit.

Am I doing something wrong here, or are these bits this useless??? All the extra fuzz on the sides makes for enough extra work to trim out and potential ruined rivet sets (and therefore ruined scale sets) that it is hardly worth it...
 
Cabnet makers trick is to put masking tape over the place you want to drill to keep it from splintering. And go slow.
 
I suggest using a machinist counterbore. This is a test piece predrilled with 1/4" Home Depot step drill, it left a ragged edge. The 3/8" counterbore has a removable 1/4" pilot and was used to bore the predrilled hole about 3/16" deep, the wood is well seasoned Osage Orange. The edges are sharp and crisp.

Counterbores are available, possibly at knife making suppliers or machine tooling suppliers.

A larger version is included in the image.

http://i32.photobucket.com/albums/d48/sarpyco/counterbore90dpi-1.jpg

These were bought at Boeing Aircraft Salvage sales years ago.
 
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The biggest problem many folks have is not pre-drilling the guide hole. I drill the scales for the rivet shaft first, then use the counter drill with a guide pilot for a flawless step seat. If you try to drill the hole in one operation with the step drill, it will have problems often.
Stacy
 
That doesn't look like a counter sink, that looks like a counter bore. It is cutting like it is dull or wasn't ground right. If you can hold it in the light and look at the cutting edge you'll see if it is dull, just like looking at a knife blade. 50 holes is enough for something like that to get dull if cutting something abrasive (osage orange for example).

Fortunately, if it is dull, it is easy to touch it up. Two things to remember, you need to keep both edges the same depth and square and you can't have negative relief behind the cutting edge. I use a sharpie to paint where I'm working so I can see what I'm cutting, I also use diamond files. But you can use good sharpening stones on HSS. Or you can touch it up on your knife grinder, just be mindful of your angles and use a light touch and remove as little as possible.
 
Thanks guys!

The pilot hole was drilled with a 1/8" bit, so the pilot is enlarging the hole slightly. I figure that holds it more steady.

Most of it's holes have been through mesquite, which is quite hard, though I expected better from a cobalt bit. I'll give the tape and sharpening a try...the bit is too expensive to throw away!
 
I have made my own counterbores and have had counterbores made at the local machine shop. The ones I had made worked the best because they were the proper angle and very sharp. By the ripped edges on your holes I say it needs to be resharpened. It helps to spin fast but feed slow too.
 
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