forstner bit extension issues

[Erik Johanson]

I recently bought a forstner bit extension for drilling out the center of a grinder mill. Everything was going along just fine and then bam, the bit will no longer allow me to feed it into the material. I attempt to extract the bit to investigate my problem and I quickly found the issue. The set screws on the dang extension must have vibrated loose and came undone from my forstner bit. After about two hours of trying to get my bit out of the blank I thought OK, maybe I didn't tighten it down enough. So, I cranked those babies down as hard as I could and this time decided to mount it in the drill press instead of doing it on the lathe.

Nope no luck, except this time the set screws didn't loosen up they fell out and got chewed up by my forstner bit. So while I am shopping for new set screw to make my $15 POS work, I was wondering if anyone else has had this issue or am I just tool dumb?

I was thinking of putting some loctite on the threads but wasn't sure if that will help? Would grinding a flat spot on my forstner bit help too? (I am reluctant to try this only because of the cost of those little buggers and I would hate to ruin one)

Any help would be greatly appreciated.

[Sid Matheny]

I use the Colt bits and extensions and they don't have set screws.

Sid

[Tim Rinehart]

+1 on the Colt forstner bits...best forstner bit out there I think. They have a very nice design on the engagement to both the extensions and to the morse taper adapter that can be placed into the tailstock in place of a drill chuck. The feature is called rotolock or something like that, and it maintains very good straightness...and it won't loosen. The harder you drill...the harder it holds via the eccentric gripping feature.
The other cool feature of these bits is the way they break chips to reduce clogging.
I bought mine from Infinity Tooling, best price I could find at the time.
Good luck...I gave up on my use of extenstions for other forstners...if they aren't long enough on their own, out come the Colts.

[Richard Jones]

Erik,

I took the bit to the grinder and made a flat spot on the shank, just enough so that the screws would have a nice spot to land on. No more set screws backing out.

R