Gundrilling 101

I have a need for several 0.350" holes 10.5" deep in 4140 rod...

Been looking to buy something close, no joy so far.

I came accross this gundrilling FAQ. It states gundrilling can be done on a CNC lathe like mine.

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Anyone have experience with gundrilling on a CNC lathe? I know i can't go with the high pressue oil I've seen on regular gundrills. The above FAQ mentions a spray mist system. I could go with high flow coolant as my CNC lathe is enclosed.

Anyone know how gundrilling was done 100 years ago? Bet the same technique would work today.

Karl

Reply to
Karl Townsend
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100 years ago was still gun drilling times like current methods. Prior to that the barrel was hammer formed over a mandrel.
Reply to
Steve W.

How did they manage to maintain accuracy under such conditions? Or did each gun just end up having "character"?

And how did they get those poor monkeys to sit still for such abuse?

Reply to
Tim Wescott

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Probly find some info here <

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> they are probably the largest US firm

Used to do a lot of it at the lazy b but usually in round rod if it was important that the hole be perfectly centered at both ends then we'd just go ahead and let the drill wander...re-pick-up hole center at the exit end after the fact and then finally we'd finish the OD

Reply to
PrecisionmachinisT

I have a need for several 0.350" holes 10.5" deep in 4140 rod...

Been looking to buy something close, no joy so far.

I came accross this gundrilling FAQ. It states gundrilling can be done on a CNC lathe like mine.

formatting link

Anyone have experience with gundrilling on a CNC lathe? I know i can't go with the high pressue oil I've seen on regular gundrills. The above FAQ mentions a spray mist system. I could go with high flow coolant as my CNC lathe is enclosed.

Anyone know how gundrilling was done 100 years ago? Bet the same technique would work today.

Karl ______________________________________________________________

How good do the holes have to be?

Reply to
Tom Gardner

If you go further enough back they probably welded the barrel around a mandrill and then reamed to size. But in reading several books by various gunsmiths who were in the trade in the early 1900's, they drilled the initial hole somewhat undersize and then used special reamers to straighten the hole and bring it to size. They probably also straightened the barrels as a final step.

The U shaped drill tubes and the pressure oil feed down the tube both lubricated the drill and flushed the chips out of the hole. The actual cutting bit was a single flute drill and the drilling machines were said to be high RPM and low feed rate.

I'm sure that you have looked at the web but this site is pr

For a more detailed look you might try

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is a sort of modern method of doing it the way it used to be done :-)

or Lilja's site

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All of the instructions I have ever seen emphasized the "U" shaped drill rods and the high pressure oil to wash the chips out of the hole.

-- Cheers

John B.

Reply to
John B.

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jsw

Reply to
Jim Wilkins

thanks for the links. I'll order that lindsay book.

Reply to
Karl Townsend

See Howe's "The Modern Gunsmith". Has the complete setup, drill bit shape, support, plumbing, everything. The bit, when properly shaped and started, is self-centering. Lindsey had a book on making rifle barrels, mostly extracts from WWI-era machining magazines. Has a little more on the pitfalls and problems seen in production. The old- timers used high-pressure cutting oil for clearing chips and lots of it. The Lindsey book mentions a basement of oil tanks and gutters in the machine room for oil return. It isn't that coolant isn't needed, it's the chip clearing function that needs the flow, I doubt if a mist will do that.

Stan

Reply to
Stanley Schaefer

mine.http://www.sterlinggundrills.com/frequently_asked_questions_about_dri...>>

Stan, what about peck drilling with CNC? It may take a lot longer than with high pressure oil, but it should work, right?

i
Reply to
Ignoramus17548

Thnaks, I found the book on the net and downloaded it.

Reply to
Karl Townsend

I'd buy a bunch of the drills and a high pressure pump. Just don't have the room for another machine. Looks like the CHNC will do a fine job for my needs

Karl

Reply to
Karl Townsend

Ignoramus17548 fired this volley in news:NbCdnV3jrr9LcKrSnZ2dnUVZ snipped-for-privacy@giganews.com:

Ig, peck drilling holes deeper than about 10xD tends to bell the mouth of the hole.

A common twist drill isn't terribly rigid, nor terribly straight, as tools go. It wiggles just a bit about its center, even if it's accurately sharpened with the tip exactly centered. And any runout in the setup, spindle, chuck, collet, or arbor exacerbates that.

So, although it tends to self-center IN the hole, it doesn't make a hole exactly its own diameter until it's fairly deeply embedded in the work.

Pecking worsens that, because each time it enters the hole, it deepens that enlarged part of the hole. The hole ends up somewhat "bell shaped", more and more, the more pecks that are taken.

That's fine for (most) bolt holes. Not for a precision bore.

If he needs "just a hole", peck drilling will work fine. If he needs an accurate "bore", no.

Of course, one can drill undersized by a couple of thou, then ream to size.

LLoyd

Reply to
Lloyd E. Sponenburgh

Greetings Karl, I have several drills with coolant holes in them that range in size from less than .300 to about .750 dia. Some of these drills are over

12 inches long. Even the skinny ones. They have a threaded shank with a beveled shoulder and thread into a coolant inducing rotary union. The union has a shank that goes into the spindle and drives the drill. They were originally used on a big CNC mill for drilling deep holes in steel parts. I can try to find out who makes them if you would like. They might be just what you need. Eric
Reply to
etpm

When it comes to drilling straight holes, the through-hole coolant is not the big issue, Eric. The big issue is single-point cutting with a "backside" of the cutter that bears on the hole as it's cut.

It shares some characteristics with single-point boring -- primarily that the deflecting load on the cutter is uniform around the periphery of the hole -- but it's different in that the tool actually bears against the hole, making rigidity of the drill shank a minor issue.

If you start a gundrill straight, and if the material you're cutting is clean and homogeneous, it will cut straight, even though the drill shank will flex.

This is not true with any kind of multi-edge drill, whether it's a conventional twist drill, or an insert type, or a spade drill.

The high-pressure lubricant/coolant is necessary because this kind of cutting is a chip-jamming nightmare. You absolutely need it beyond certain very low depth/diameter ratios.

Reply to
Ed Huntress

ED, The last shop I worked in had several gundrills. We drilled holes from as small as 1/16" to over 2". I learned how to sharpen gundrills and understand how they work. I can't count how many bushings I made for starting gundrills on location. The drills I have are Guring drills and the guy I got them was drilling very straight holes with them. I know they don't work the same as gundrills. Being used in a mill may be why they drilled such straight holes because they were fed straight. They didn't require really high pressure coolant to clear the chips. But I watched them drilling parts and the drills were being pecked. Unlike gundrills which just keep on going. Eric

Reply to
etpm

Sometimes a fat piece of metal was heated up, put over a mandrill and run through a rolling stand. Then it was re-heated, placed over a smaller mandril and run through again. Repeat until you get what you want.

Sorry for not answering your question but drilling a long hole a long time ago was hard to do so they found another way.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Reply to
Wes

Since you spelled the name phonetically;

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jsw

Reply to
Jim Wilkins

There are several techiques for drilling straight holes, including using a combination of workpiece rotation and tool rotation (used in high-end gundrilling, too). And Guhring makes very accurate cutting tools.

But once you exceed the depth ratio that allows the drill shank to contribute to centering and if you take away that bushing effect opposite the cutting edge, you're depending on everything being near-perfect: -- which it rarely is. Multi-spindle production gundrilling machines actually are pretty crude machines, or they were.

Pecking and multiple flutes, too, will make clearing chips a lot easier. I've watched gun drilling at Colt, Remington (back in the '70s), as well as some ECM gun-barrel operations, and I was always amazed at how they could center those holes so well in all of that lubricant mess and with all of that rattling going on.

I don't doubt your success at drilling straight holes with other drills, Erik, but I think it takes more than a good drill bit to do it.

Reply to
Ed Huntress

Oh crap. I know better. I should spell check better. I had just looked at the drills about 30 minutes before the post too. Eric

Reply to
etpm

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