OT - Any Bearing Experts (Thrust Problem)

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Turns out, 6901... But I was wrong. there are thrust bearings on the head. Can you tell I'm not the designer?!?
Customer just told me another interesting tibdit... They are breaking drills (twisting them apart in the bushing) so there is definitly a set-up problem on their end... We shall see!
Regards, Joe Agro, Jr. (800) 871-5022 01.908.542.0244 Automatic / Pneumatic Drills: http://www.AutoDrill.com Multiple Spindle Drills: http://www.Multi-Drill.com Flagship Site: http://www.Drill-N-Tap.com
V8013-R

On Mon, 2 Mar 2009 15:45:54 -0500, "Joe AutoDrill"
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<snip> ----------- Thanks for the Paul Harvy memorial "rest of the story."
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

Joe AutoDrill wrote:
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I'm guessing that you're using a pair (or more) of angular contact ball bearings. Higher ABEC rated (more precise) bearings will probably last longer, just because they fit and roll better than the cheaper versions. Also, ACB's come in a variety of different contact angles, which have dramatically different characteristics in terms of how much radial or axial load they'll handle. Bigger angles give more trust (axial load) capacity, but less radial. Drilling is almost all about thrust and torque, not radial loads.
Also, if you're using more than two ACB's, you'll want to think about how they're stacked. A simple pair, arranged face to face or back to back, will carry the same axial load in either direction. But with triples or fourples, you can stack things heavy in one direction.
I'd look at improving the bearing type, rating, angle, rated capacities, and arrangement, before doing any kind of major re-design work.
KG

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Random suggestion. Admittedly I have not cruised though all the posts. Have you looked into different tooling? TAlN coated parabolics - Garr Tool or Titex, 130 to 150 deg tip angle. Reduce the tool pressure and the bearings may come to you. We had excellent results in pre-hardended (RC28-35) 4130 with this style of tool, reduction of spindle loads 10-20%.

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Not to be a dickhead here but 4130 at 28Rc really isn't "hardened" rather that's basically drawn back down to be only very slightly above an annealed state.
Your point ( I think ) stands though --use a high helix and split the point completely to center and IIRC your thrust req drops almost to zero....and the softer the better...

JL wrote:
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Good thought. With a typical "chisel" point drill, forces are about 30% torque and 70% thrust. With a good high performance drill (I'm partial to Sumitomo), the point can be split down to almost nothing, so nearly the whole thing is cutting edges instead of being so much chisel. The torque/thrust ratio can be reversed, and can often get close to 80/20. A big improvement on almost any application or machine.
KG