Drilling on a manual lathe

Awl--

Because the drill does not rotate in the tailstock, deep-hole drilling can be a *real* pita, esp. with coolant so difficult to apply. Typically a 3/8 drill, about 2" deep, in 6061 alum.

Is there some kind of electric or air rotary tool that will fit into the tailstock, to give the drill some spin? Don't need much, as the work is turning--mebbe 500 to 1,000 rpm on the drill. Variable would be nice, but I'll take anything. I'm getting close to doing some production work, and this would really make my life easier.

Reply to
Pre-Meltdown
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Why are you having trouble with coolant? Most people think that coolant is a lot *easier* with a stationary drill bit. When the bit is spinning, the flutes are always trying to screw the coolant back out of the cut. When it's stationary, you can just aim the nozzle in there, and, except that the chips are fighting you, you do have a better chance to reach the cut as the coolant follows the stationary flutes.

At least, that's what the applications engineers used to tell me. To a limited extent, that's also been my own experience.

-- Ed Huntress

Reply to
Ed Huntress

"Ed Huntress" wrote: Why are you having trouble with coolant? Most people think that coolant is a

^^^^^^^^^^^^^^^^^^^^^ I have heard that rotating both the bit and the work produces a straighter bore, but I have never understood why. In fact, I doubt it. What matters is the relative rotation between the work and the cutting edge. If the bit is rotating, doesn't that just add to the cutting speed?

Reply to
Leo Lichtman

It does, but the main advantage is that when the drill itself spins, it powers/augers the chips out. When the drill doesn't turn, the chips tend to clump/bunch up, causing binding, sometimes making it difficult to remove the drill from the hole. Proly worse in alum than in steel. I can drill *much* faster in a mill than in a lathe.

Reply to
Pre-Meltdown

It does produce a straighter bore. In fact, gundrilling machines usually work that way. I've thought about it in the past but I've never come up with a convincing reason why it works.

Yes, a rotating bit adds to cutting speed.

-- Ed Huntress

Reply to
Ed Huntress

The holes are straighter because of...GRAVITY! I sh*t you not.

This is from the floor engineneer at a shop that does LARGE gundrilling in SoCal: by turning both the part and the drill, you cancel out the droop of the drill bit as it extends away from the guide bushing.

Now, the part in question was a chunk of steel 6.5 FEET in diameter getting a 33.25" hole 36 FEET deep...gawd that was impressive to see the chips coming out and using a large bobcat-like digger to handle the chips.

Mike

Reply to
The Davenport's

Wow. Gawd, that's drilling.

Yes, I've heard the gravity story. I read a couple of books on gundrilling when I wrote some gundrilling articles for American Machinist a long time ago. I don't question it but the machine tool that runs inside my head, which I use to understand such things, just wouldn't cooperate. d8-)

I can imagine the force of gravity pulling the drill down, but then I see (actually, feel) the force on the bottom side of the drill bit building up as the bit droops, and then the work rotating and the bottom of the hole becomes the top and the force pulling the bit down now is working on the

*opposite* side of the work, evening out the hole....

But I shouldn't go there, because it doesn't work that way in practice. I've seen the results of rotating both the drill and the work and there's no question it produces a straighter hole.

It's pretty neat, in any case. And then there's the ECM gundrilling (gun eroding?) used by some companies that make rifle barrels...but I digress, as usual.

-- Ed Huntress

Reply to
Ed Huntress

I think that it is more likely the effect of gravity, not on the drill, but on the swarf. any swarf that bunches up unevenly in the flutes of a drill has a reasonably good opportunity to jack the drill to the opposite side of the hole.

if you look at your successful drillings you backed out often to remove the swarf. your unsuccessful drillings, if they're like mine, are where you got lazy and let the swarf accumulate in the drill flutes.

it is a truely interesting problem. how do you drill a 4.5mm hole a yard into a rod of steel and have the hole stay straight for the entire length?

Stealth Pilot

Reply to
Stealth Pilot

I don't see the problem. We drill 11/16 dia holes 4" deep in Al on the lathes all the time at school. Even the students don't seem to have a problem. We use the carriage as a stop to make clearing the swarf easy. ...lew...

Reply to
Lew Hartswick

On Wed, 28 Nov 2007 05:33:33 -0600, with neither quill nor qualm, "The Davenport's" quickly quoth:

Hey, Mike! Please take a video camera the next time you go there and bring us back a video of the scene. It sounds wild!

-- Don't bother just to be better than your contemporaries or predecessors. Try to be better than yourself. -- William Faulkner

Reply to
Larry Jaques

Well, let me clarify "real pita": much more pecking than if I were doing it in a mill.

Might be an inneresting experiment in school: same hole, lathe vs. mill drilled. Measure coolant used, pecks needed, overall time to drill hole. I'm willing to bet that considering the cranking necessary in a tailstock (no real "rapid", and gravity not helping with the coolant, the answer is on the order of 2:1. Ed mentioned the stationary drill not fighting the coolant in a lathe, but I'll bet gravity is more of a help in a mill.

Reply to
Pre-Meltdown

Gundrilling is half art and half science. It's always impressed me as a subtle metalworking skill.

-- Ed Huntress

Reply to
Ed Huntress

Oh, yeah, it probably is. I thought you were comparing a stationary bit in a lathe versus a rotating bit in a lathe. At Wasino, on the gang machines, we generally drilled from the cross slide, either with rotating drills or stationary ones. If you could get away with it and if you were using through-hole coolant (we usually did), the setup for supplying coolant, not to mention the lack of a turning drill spindle, was a lot simpler and cheaper with the stationary bit. If you weren't using through-hole coolant, I was told that the stationary drill gave fewer problems with getting coolant to the cut.

-- Ed Huntress

Reply to
Ed Huntress

Hey! All this talk about gundrilling has got me wondering. Has anyone seen Guy Lautard's video re. rifle-building in the home shop? I've wondered if it details pumping coolant through gun drills. Somewhere in the back of my mind is a scheme whereby that is done via an automotive type of oil pump. But then there are the nagging questions re. sealing and rotating the headstock drill. Help!

Gundrilling is half art and half science. It's always impressed me as a subtle metalworking skill.

-- Ed Huntress

Reply to
Robert Swinney

I suspect that several things might make your task easier. Try increasing the speed to about 1275 RPM and keep an eye on the chips. You should have two nice spirals continuously.

You might get better results if you thin the web of the bit and or drill a pilot hole.

I don't think that 2" on a 3/8 dia. hole should cause you much grief.

If you have a tool post chuck, sometimes it is a lot faster to clear the chips. You might also experiment with just pushing the tail stock rather than cranking the wheel in and out. Think about rigging a lever (think turret lathe) if you are going to do a production run. Adjust the locking nut on the tail stock so the tail stock will slide on the ways freely but won't wobble.

Reply to
Roger Shoaf

I've got an Aloris Morse taper holder. I find it WAY faster to mount the drill on the carriage and peck by moving the whole carriage. Clamp a stop for production work. Or, just use the DRO. I use a Hench type coolant sprayer to blow off chips and cool. Plenty of leverage for all but big drills, then engage the power feed.

Karl

Reply to
Karl Townsend

Guy Lautard's video re.

through gun drills.

automotive type of oil

headstock drill. Help!

Power steering pump, or a simple gear hydraulic pump. IIRC the vid shows a gear pump, and suggests a PS pump as alternate. Pressure was controlled by a simple bleedoff back to the reservoir.

The drill is static, the blank is rotated. The cuttings and used fluid are able to make it to the chip box via a close fitting drill bushing. A spray shield keeps the leakage on the machine.

I kinda got my doubts that gravity is able to counter the drills ability to stay as near as possible to the axis of the shaft being drilled, under load.

A gundrill thats an order of magnitude bigger (like too heavy to lift by yourself into position) maybe different, but in rifle barrel sizes, I think cutting loads trump gravity over the length of cut involved here.

Cheers Trevor Jones

Reply to
Trevor Jones

Wow. Two inches deep and looking to make life that much more complicated!

If you are having issues with a hole that size and depth, I would suggest a good look at the tailstock alignment. And the way the drill is sharpened, if it is a resharp.

Two inches is not even the full length of the flutes on a 3/8" drill.

Get on with it! :-)

Drill undersize, and make the bottom square, and the sides to size and tolerance with a boring bar.

Cheers Trevor Jones

Reply to
Trevor Jones

Yeah, I know, not a big deal, just so slow compared to VMC drilling. Some good suggestions here and in amc, but I really think a rotating bit would speed things up greatly. Haven't found anything that fits in a tailstock, so apparently not many share my sentiments.

Reply to
Pre-Meltdown

I would try different cutting angles and different speeds and different types of coolant. 3/8" x 2" deep is not deep at all.

I just drilled two 1/2" holes, 3 1/2" deep through steel with a hand drill! It wasn't fast though. Probably took 20 - 30 min. per hole. I drilled a 1/8" pilot hole 2" deep first without breaking the drills

I'm not sure I believe the gravity statements. Gravity affects the drill because of its mass. Spinning it around doesn't change the mass. ie Turbine rotor sag.

Spinning the drill and the part probably makes a straighter hole because any inequality in the sharpening of the drill in nullified by rotating it it. Just my two cents. Probably wrong.

Reply to
Dan

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