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Small diameter, deep hole drilling in aluminum...issues.

Liberty_Machine

Liberty_Machine

Aluminum
Joined
Feb 28, 2017
I'm working on a project, mat'l is 6061-T6. Hole diameter is .098"+.003/-0. Depth is only 1.125". I approached the job in what I thought was a safe manner; stub screw machine Titex parabolic to drill a pilot hole, followed up with a Titex parabolic jobber length drill. It's resulted in an oversized, bell mouthed and tapered hole, taking a .101" pin almost half depth. Running a G83 (it doesn't come out of the hole) at S3000, F5., Q.03". What am I doing wrong? Drills are new and have zero runout. I've got a boat load of these parts to make, it just might make sense to move to an oil hole drill, I've heard really good things about the Mikron "Crazydrill"
Does coolant have an impact on this? My coolant (Oemmeta) is slated for a change out, but it's still looking decent on the refractometer. Oh, running coolant through the collet, as the Mori only has so much adjustment in the nozzles and I've got them aimed at other critical tools.
 
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I’m assuming you are running it dry? I usually have pretty good luck with those drills. On drills that small I start out my pecks at .06”. Full retract. 140sf @ .0025” feed. I start tweaking up once I get a hole to the right size


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If you only drill 1/4" deep what is your hole size? If your shallow hole is good on diameter it is probably a chip evacuation problem. If your shallow hole is oversized your drill isn't behaving for some reason.
 
Lathe or mill? If lathe, have you indicated the toolholder to make sure everything is lined up? Turret a little off will make an oversized bellmouthed hole. If mill, 3,000 RPM is pretty slow. I would run that at 6,000 in the mill.

And no, you're probably not going to have a good day trying to run that drill (no thru-coolant) that deep in one shot.

Regards.

Mike
 
No, I didn't think "one shot" with a HSS parabolic was ever a good idea ;)
VMC, Mori Duravertical 5100, high pressure coolant (flowing around collet)
 
I've never had much luck with parabolic drills. They seem flimsy, with much less core than a regular drill. I suspect the parabolic drill is whipping a bit when the going gets tough down in the last 1/3 or 1/4 of the hole and the thrust requirement goes up.

I'd try a standard-form carbide drill.

BTW, you said you're using G83, and then you say "it doesn't come out of the hole". My understanding is that G83 is a full retract between pecks. Is it not fully withdrawing because your R value is where the pilot drill ended? If so, then it's likely the swarf is not ejecting between pecks, since it has to travel a lot farther up the flute before it can clear. One way or another, I would make sure the long drill fully retracts between pecks.

Regards.

Mike
 
I do use and prefer Titex parabolics for all the holes in 6061 I drill but find I get tighter tolerances with carbide so that's a thought. Not that your hole and drill stickout are all that deep or long but when drilling deeper hole to diameter ratios I find I get harmonics when rapiding out of the hole too fast so turning down the rapids may help.

What is your R value for the deep drill? When doing what you are I often set it to -.1ish. Might as well just post your entire G83 code so we see your pecking values as well.

My gut hunch is the problem is HSS drills and pecking value.
 
To close the loop on this discussion; I found that drilling the pilot just slightly under (.094) and finishing up with the .098" Titex resulted in a beautiful hole, all the way to the bottom. I'd like to move to a carbide coolant through, but they don't give those away....
 
I can attest to the crazyflex drills being awesome. We bought a couple .012" (or maybe .014" ?) x .59" LOC and drilled dozens and dozens of holes in 6061 T6, all came out straight and to size.
 
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