Small diameter, deep hole drilling in aluminum...issues.
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  1. #1
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    Default Small diameter, deep hole drilling in aluminum...issues.

    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.
    Last edited by Liberty_Machine; 03-21-2021 at 08:58 AM.

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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


    Sent from my iPhone using Tapatalk

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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.

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    Edited original post to give info about coolant

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    Make your pilot drill a little smaller and follow with the onsize with no peck and a lot of feed.

    Ed.

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    At only 1.125" deep, should I just skip the pilot drill? The pilot measures .098/.099 (hole size)

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    @Atex; HSS drill, no peck, one shot, 1.125 deep....

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    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

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    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)

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    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

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    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.

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    Quote Originally Posted by Liberty_Machine View Post
    @Atex; HSS drill, no peck, one shot, 1.125 deep....
    Drill your pilot any way you wish then follow with the on size. Constant pecks will bell the mouth of the hole. I would peck drill it about .008 under then follow with on size and no peck.

    Ed.

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    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....

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    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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    Harvey Tool
    Use g73 instead of g83. Are you on mill or lathe? Mill would be better.


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