deep hole question

I am drilling 13/64 holes 2 inches deep in 6061. The bottom of the hole wanders as as much as 0.020-0.030 off center. What is the best straightness I can hope for on a hole that size, that deep?

Any drill sharpening, etc, hints?

Thanks

Reply to
Bill Chernoff
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straightness

Can you bore it with a single point tool ???

Reply to
PrecisionMachinisT

Are you drilling in a lathe, mill, or drill press? What kind of drill & fixturing,,Jacobs chuck, morse taper drill, ?? Is the drill new or has it been resharpened? Are you center-drilling prior to drilling? Is the work being moved after the center-drilling or is it done sequentially? How are you feeding the drill, and at what feed rate? Higher feed rates = more error.

With a proper setup I would expect you should do better that 1/32" that you are getting now.

straightness

Reply to
Tony

No shit! Hell, I work closer than that with a hatchet. A dull one. Uphill, in the snow, both ways. ;~)

Even Sam could probably do it.

michael

Reply to
michael

straightness

I didn't know it was possible to wander that much, you can do WAY better.

  1. Clamp your part down so it won't move.

  1. Spot drill or center drill first. This gives you a starting spot that won't wander.

  2. Make sure your drill is properly sharpened. A fellow named Teenut wrote the best ever drill sharpening post on this NG if you don't know how. I've reposted it at least twice under the author "Teenut in Heaven". Look it up at google.com

Karl

Reply to
Karl Townsend

Back in January Sy Wexler posted a message with the mil specs on hole tolerances. You will find it if you go to google groups and search for snipped-for-privacy@aol.com and How straight are drilled holes. Lots of good info.

Dan

Reply to
Dan Caster

straightness

As others have said, center or spot drill first.

No one suggested predrilling with a smaller diameter drill. Something like a

1/16" drill would be good. The web in larger drills (especially those which are dull or badly sharpened) tends to push the drill around.

Don't cram the drill into the material. Push firmly but let the machine do the drilling. Peck every couple of seconds as well. Developing a good feel for how a drill bit should be drilling is important on manual drill presses. This feel can tell you when the machine is about to toss your piece, break/melt your drill, or drill a straight and correctly sized hole.

Slow down your RPM if you feel like you have to push hard to eliminate chatter. The standard (4xCS)/Ø formula will yield an RPM of about 6,000. This is certainly too fast. I'd go about 1000. It won't hurt the drill and (if you don't have hundreds of holes to do) time should be ok too.

HTH.

Regards,

Robin

Reply to
Robin S.

Hey now!!!

I do at least *occasonally* read this group.............

Suggest first center or spot drill, to a diameter slightly greater than the finish hole size, then drill through with a slightly undersize drill, perhaps one of them fancy parabolic flute types.

And, as I hadnt noticed at first the depth / dia. ratio here--next, I would probly finish the hole with a 3 flute core drill.

For even better results, I would bore with an endmill to a very slight depth using an endmill that is the desired finish size, just prior to the core drill operation.

Finally, all of this is out the door if your quill or knee travel is not

  • exactly* parallel to your spindle bearings rotational axis.

Cheers,

Reply to
PrecisionMachinisT

No, you *see* them bend. When I was drilling that deep hole in the nickel-iron tubing, I didn't want the material to work harden - so I was pushing the drill pretty hard. When I went too far it went beyond the column limit and bowed out a tad... so I backed off a bit.

Honestly for this one I have to agree with Dave here. There is simply no way I would be able do do as good a job as Gurhing with pointing one of their drills. That the holes came out as good as they did (about two thou out over an inch) I attribute mostly to their drill sharpening prowess.

For larger drills, yes. But for the smaller ones (and remember, I'm advocating pilot-drilling deep holes) there is no way the HSM can do as good a job as the manufacturer.

Jim

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Reply to
jim rozen

I was taught by a skilled machinest long ago to first drill with a drill bit that is the same size or slightly bigger than the web of the drill needed for the final hole. I think this is what Robin means by the 15-30%. If you are going to drill a 5 mm hole then use a 1 mm (

20% of 5mm ) pilot drill.

But for holes up to about 5 mm I usually don't use a pilot drill. But for a 25 mm hole, a 5 mm pilot hole helps me. Try it and make up your own mind.

Dan

Reply to
Dan Caster

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