Will a cobalt drill bit work for this?

[snorkel]

I need to bore out a LB7 blade to 1/4 and then install a bushing to restore the blades pivot hole, which became oblong instead of round.

I ordered a cobalt bit for the drill press and I hope that will work, has anyone done this before?

Thanks,

Snorkel

[rangerbluedog]

possibly, but the drill won't last long. A solid carbide drill would be better.

[knifemaker3]

since you stated that the hole is oblong instead of round it might work. If the blade is at a proper hardness for a knife blade it will not work. A blade at proper hardness should be at least 56 Rc on the rockwell c scale. If the pivot hole has become oblong from use then I would say the blade is not properly hardened as the hole shouldn't wear, instead the softer pin material should wear, break, or become deformed.

So, short answer is no it won't work. Long answer is it might depending on the hardness of the blade in the pivot area.

Good Luck!

[snorkel]

Just a FYI, cobalt bits have a 65.5 to 67 Rockwell C hardness so woudn't they work on 440c blades?

[rangerbluedog]

opah! That being the case, they should work fine. I don't think the blade is that hard. It's most likely in the 50s HRC if that. And even then, if it were induction hardened, the tang area might not be that hard.

[knifemaker3]

I'm not going to get in an argument here with you. But in 21 years of making knives I do know not to drill a properly hardened blade with a cobalt bit. It just won't last unless the blade is not very hard to begin with. Just my opinion but if you can drill it all the way without ruining the drill bit, I wouldn't want the knife as it ain't hardened properly.

Use a solid carbide bit and you will not have any problem with a properly hardened blade.

I will tell you to be sure and flood, and I mean keep it flooded, with a coolant when trying to drill.


But, since you stated that the hole is oblong I'm suspecting it ain't hardened very well and you might just get by with it. Try it and see.

Good luck!

[rangerbluedog]

No argument from me, I's just an old machinist - don't know nuttin' 'bout knife makin'

[snorkel]

The cobalt bit indeed worked, but it's so close in hardness it was taking forever, so I went to the local Menards (home depot like store) and they had a quad blade carbide bit for tile and glass, and that cut through it like butter, no problem at all and the bushing fit perfectly.
Just a FYI, that bit only cost 8.99 and worked incredibly well.

Later,

Snorkel

[rangerbluedog]

Congrats Snorkel!
Glad you were able to "git 'er done".