Gundrilling 101

Karl Townsend · 2012-02-12T01:43:31+00:00

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 doneon a CNC lathe like mine.Anyone have experience with gundrilling on a CNC lathe? I know i can'tgo with the high pressue oil I've seen on regular gundrills. The aboveFAQ mentions a spray mist system. I could go with high flow coolant asmy CNC lathe is enclosed.Anyone know how gundrilling was done 100 years ago? Bet the sametechnique would work today.Karl

Feb 12, 2012 25 Replies

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etpm 14 years ago

Well sure Ed. It takes a good setup too. With gundrills getting the hole started is key. With thinner drills we had to use whip guides on the unsupported shank of the drill before it entered the hole. But the guides were fairly loose so the shank on thin drills would still whip around in a small circle. And the noise from the larger drills when drilling some materials was so loud we all had to wear earplugs under ear muffs. I'm still surprised the carbide tips didn't fracture from the chatter that was making all the noise. We used hardened bushings honed to the drill tip's exact size to insure a good on size start to the hole. Eric

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Ed Huntress 14 years ago

Hah! Yes, that sounds familiar. The rattling and whipping around were the biggest surprises to me when I first saw gundrilling operations. Here was a high-precision machining operation and it sounded like a cross between a popcorn popper and a Caribbean steel band.

Well, I've spent some time with the Guehring people and I have the highest respect for their tools. I'm sure your experience with those setups can teach us a few things.

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Brian Lawson 14 years ago

Hey Karl,

No expert here, but gun-drills and gundrilling require the high pressure "oil" . It is not there so much as a lubricant, but to remove the swarf as it is generated. If the swarf is not removed, it won't drill, or at least not straight. Just "lubricating" or coolant won't cut it !!

Assuming that you can get high-pressure through the drill, CNC should work fine, although if it is a long bore you will need some sort of shank support.

All the accuracy in a gun-drill is in the form of the tip. Look very closely at how it works.

Take care. Good luck.

Brian Lawson, Bothwell, Ontario.

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tnik 14 years ago

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Karl,

We gun drill in our CNC lathe some. We end up hooking up a pressure washer to the coolant lines and use that as a high pressure pump. It works pretty good. Also we gun drill on our horizontal mills, it goes a bit slower, but works for what we need.

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tnik 14 years ago

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Also, we normally either have a bushing help to start the hole, or we bore and/or ream a pilot hole. Once we have a straight hole to start the gun drill, it goes nice and straight.

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Karl Townsend 14 years ago

Thanks, good to know this has been done. Just what i'm going to try. Could you give me some speeds and feeds for the size drills you've run?

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