Reamer drill size for titanium?

I'm going to be reaming .077" holes in grade 2 titanium and want to choose a drill that will leave as little material as possible for reaming. I haven't worked with titanium before, and am concerned about the hole going oversized during drilling. I know about titanium's workability, just would like an experienced person's advice on drill size for a hole this small. I don't want to break a reamer. Thanks.

Drill 1/16 , Carbide Reamer

Hi Forestgnome:
Titanium is shitty to ream because it tends to grab on the cutting tool and will twist off a reamer in a heartbeat as soon as you get even a little bit into the hole.
I've had best success with carbide reamers as upnorth suggests, but I avoid reaming wherever possible and either mill or bore the holes to size or wirecut them if I can.
Of course, sometimes you can't, but I always grit my teeth and expect to break reamers and trash parts.
Back tapering the reamers helps; so does running them slow and feeding them briskly but both of these methods can play havoc with your precision and finish, so test it on scrap first, and buy extra reamers!!

You need something for the reamer to cut, but upnorth's suggestion of 0.007" per side feels a bit optimistic to me.
I'd probably try to go for 0.003" per side, but that's just a guess on my part.

Cheers

Marcus
Implant Mechanix – Design & Innovation - home
Vancouver Wire EDM -- Wire EDM Machining
Clarus Microtech

I always use 7% x the finished hole dimension to find the drill size, hasn't failed me yet....

So, .077" x .07 = .0054

.077" - .0054 = 0.0716

I'd go with a #50 drill. YMMV

Isn't Grade 2 the dead soft CP (comercially pure) stuff they use in plating shops etc?

If so from my limited experience it drills and reams like budda.

Grade 5 (6Al4V) is a completely different story tho...

I am with Implex with one small deviation. I would use a #40 drill leaving .002 per side. I think .003 per side is a bit much. My rule of thumb for reamer drill sizes is 3% of the finished size.

Thanks for the suggestions. I already purchased a cobalt reamer, only one, keeping my fingers crossed. I read a suggestion somewhere else that mentioned leaving only .001" to ream, but like I said, at that number I'm afraid I would drill oversized and blow the hole. I only need to do 6 holes.

Terry Keeley said:

Isn't Grade 2 the dead soft CP (comercially pure) stuff they use in plating shops etc?

If so from my limited experience it drills and reams like budda.

Grade 5 (6Al4V) is a completely different story tho...

Click to expand...

Funny, I was just running a job in 6Al4V with a .265 reamed through hole. Got easily a couple hundred parts on the same drill and reamer, no issues. Though, we drilled, interpolated, then reamed, so the reamer was really only cutting .001-.002 per side, tops.

Any operation that involves rubbing action is a PITA in titanium. I have had reamers wring off on the way OUT. Stuff not only work hardens, it galls very easily. Get some chip powder on the cutter and it welds itself up tight. I'd go ahead and order another reamer, as well. Ti is not very hard (unless it work hardens), but it is abrasive as hell. As long as you keep sharp tools, HSS cuts even 6Al4V just wonderfully. Soon as it dulls, things go south quickly, though. In a confined hole with a reamer, there will be very little warning when it dulls, rubs, work hardens, galls and wrings off.