mini gun drills

I worked for some time with a shop that does a lot of precision deep hole drilling. I have used as small as .062 with great results. We did, on occasion run some as small as .125 in a lathe with a home made stuffing box and coolant pump.

Bill Roberto wrote in news:P638g.516$ snipped-for-privacy@newsread4.news.pas.earthlink.net:

Bill,

I've used them on a lathe in a fixed holder to gun drill down the center of a part. Here are the issues you would have to overcome in a live tool application:

(1) You have to induce very high pressure coolant into the live tool spindle. IIRC, for a drill that size you need 2500-3000 psi.

(2) If the hole is deep and the drill long you need a bushing at the very least to get the hole started true. You may also need an anti-whip bushing to keep the drill from bowing in the middle. All of the gun drills I've seen in this size range were solid carbide, so you *might* not have a problem with whip. But you still need a bushing or pilot hole to get the drill started.

A tip - insert the drill into the bushing or pilot hole first with the spindle running slowly in the CCW dirction, then start the the coolant and reverse the spindle. The coolant exiting the drill is usually strong enough to bend the drill enough so that it will catch the edge of the hole in the bushing (or pilot hole). You also don't want the single cutting edge to catch the hole on the way in so it's best to rotate CCW on the way in.

(3) You need to use a straight oil blended for gun drilling. Usually it a fairly low viscosity oil with some additives in it. Depending on the rest of the lathing operations this could be a real smokey kind of deal. In any case you will need a damn good mist collector just to deal with the mist from the gun drill. Then figure on a Hepa Filter or electrostatic precipitator to deal with the smoke.

(4) Gun drills are spendy, especially in that size. Gun drilling is also quite slow. You are probably looking at a feed rate of .00005 to .00015 IPR for a drill that size (yup 50 millionths to a tenth and a half). So it may be a more expensive hole than one made by more conventional means.

You might want to take a look at a "Crazy Drill" from Micron instead.

Dan,

His english wasn't so good and he first said "cannon drill" so I assumed gun drill. He then sketched what it looked like. A round piece of drill rod, ground half way down like a boring bar, relieve 3 degrees in the front and 3 degrees along the cutting edge, a 45 degree angle at the cutting tip, and the rod ground down about .01 minus the finish i.d. Same thing?

================ see:

Unka George (George McDuffee)

There is something to be said for government by a great aristocracy which has furnished leaders to the nation in peace and war for generations; even a democrat like myself must admit this. But there is absolutely nothing to be said for government by a plutocracy, for government by men very powerful in certain lines and gifted with the "money touch," but with ideals which in their essence are merely those of so many glorified pawnbrokers.

Theodore Roosevelt (1858-1919), U.S. Republican (later Progressive) politician, president. Letter, 15 Nov. 1913.

Bill Roberto wrote in news:ZVy8g.1044$x4.751 @newsread3.news.pas.earthlink.net:

Sounds like it. Gun drill geometry is an art in itself so the angles vary.

It could also be a half round drill that he's talking about. Half rounds are really best in soft materials like plastic, brass, and aluminum.

Poke around here for some more info on gun drills:

You might be able to get away with a twin flute gun drill on a live tool. You will still need coolant through the spindle.

Oh, and what Drill Masters call a half round drill isn't what I'm thinking about. Here's what I mean by half round:

That's a "D" half round drill, I use them all the time on brass.

Do they require a spot? Do they cut polished holes that don't walk? Have you used one at or around .035?

pawnbrokers.

politician, president. Letter, 15 Nov. 1913.

Thanks for the links George

Thanks Dan

I always use a 90 deg spot as all my parts call out a 45 deg chamfer. I have used a .062 "D" drill .562 deep in one cut & didn't walk in brass & 2011 alum. 15K parts in one run. BUT I use OIL ;)

But of course. What else is there?