Small Hole in Torlon Material Having Problems...

I have a customer who bought a machine back in '05. Since day #1, they have been trilling this material they call "Torlon PEI" with a. 0.029" drill at
around 10,000 RPM
The material is 3/8" thick and they have no problems making the hole itself. I thought they would have to peck drill it, but apparently not...
The drill rapids up to the surface, takes a controlled feed rate from 1/16" prior to the end of stroke (clean through) and retracts at rapid speed. Much like a CNC would but with a simple, but highly controllable hydraulic feed control doing the dirty work.
Now that every penny counts more, they found that the process leaves a burr on the product that they have been removing since day #1 by hand. They want to try and drill without getting that burr..
Here's the kicker... The burr is at the entry side, not the break through side...
My first thought was that they were controlling the feed rate too late and that the drill was entering the material fast, then slowing down and completing the stroke. They claim that is not the case and that the feed is 100% controlled from entry to breakthrough. They also claim that the burr shows up when entry happens and not during the process.
Anyone have any tips, thoughts or misc. ramblings on what might be causing the problem?
RPM or other suggestions, thoughts? Etc... Can't really go above around 11-12,000 RPM on this application due to machine limitations.
My next suggestion to them was to try and get a small countersink bit but they are using a drill bushing to make sure accuracy is held very tight. Can't use a drill bushing in that case...
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
V8013-R
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On Tue, 19 Aug 2008 15:49:26 -0400, "Joe AutoDrill"

Make a small champhering tool to go on the drill bit shank
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I said:

Because:
Their bushing is very close to the work piece. No room for a larger diameter "clean up" process.
--


Regards,
Joe Agro, Jr.
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Joe AutoDrill wrote:

well, if a csink is out of the question..
try different angles on the drillbit?
try a small peck while it is entering the material..
pray to the hole gods that they make it work for em.. ;)
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Drill may be entering the work too slowly, allowing it to wobble slightly as it tries to bite into the material. This will occur with softer materials as it pushes away from the drill. If it were hitting in rapid a bit, it might just help.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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Anthony wrote:

Or just bellmouth the hole. The way to cure tool wobble is to get hardware that doesn't and use it instead. Hopefully Joe will let us know how things go.
--

John R. Carroll
www.machiningsolution.com
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Joe,
Is it a carbide, high speed, cobalt or powdered metal drill ?
Assuming the guide bushing is lined up properly in all ways.........is it?
Try contacting Dave Burton at Performance Micro Tool www.pmtnow.com and I know I have been recommending him in here but for a good reason. His "large" tools are 1/8" diameter. He knows small drill and endmills.
I'm thinking drill point angle or geometry on the tip, edge prep, split point, something to engage the cut easier into the surface. Like 90 degree angle?
The 10,000 RPM comes out around 75 SFM which doesn't seem too severe either high or low, but heat is critical in this stuff. Not enough and the tool is chunking chips out, too high it melts the stuff.
JR
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HSS
As best as I can tell, it is. Very close to the work so as to keep the drill from deflecting on entry, remove any residual runout in my drill's spindle (bah humbug), etc.

I'll have them do just that.
CLIP
Thanks for the tip.
--


Regards,
Joe Agro, Jr.
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Joe,
torlon is PAI. Ultem is PEI.
    Drill geometry. We had a similar problem in soft copper (sheet, of course) Switching to a high perf, carbide circuit board drill was the best non-custom drill point solution, in that case. The burr was worse on entry than exit IIRC.
The burr is actually created by the drill pulling up/into the material as it enters. One solution proposed (after the fact) to me by a toolmaker was to hone the drill edge with a negative rake, so the drill pushes into the material rather than getting pulled. Not sure this will help with Torlon.
They might need a custom grind. Torlon is really tough, impact resistant.
.029 is pretty small, but I wonder if you could find a custom grinder to do a collapsible Cogsdill solid style chamfer tool, that would expand just enough past the drill bushing, if there was a way to do a second op.. just a crazy idea.
ca
Joe AutoDrill wrote:

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clay wrote:

Your copper material was probably grabbing the drill. Negative rake on the tool damped some of that out. The problem Joe is having is that the non rotating tip of a .029 drill is probably almpst twenty percent of the diameter. It's rubbing and melting the plastic and making a shape about like the rim of a crater.

This was my response to Joe in another group. You guys have him scared shitless about cross posted threads so he doesn't do it.

It isn't really a burr Joe. They are melting the material when the drill enters and you have a slight bulge. Have them look at their "burr" under a microscope.

Make up a drill with two diameters - .008" for .03 and then the full diameter. The Torlon will flow and set again before the larger diameter catches it and what has "flowed" outward from the point will be removed cleanly.
Also, use a 142 degree point geometry.
Lastly, advice is worth what you pay for it and sometimes not even that!
--

John R. Carroll
www.machiningsolution.com
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I wish the customer had a microscope camera or something to send me a photo of the burr... I think you are correct with the "crater lip" burr, but no definitive answer can be given by the customer over the phone...

I've been in newsgroups since the dawn of time... It's not "them" that has me scared, it's the over-reaction of the ISP who believes them when some yahoo claims I spammed him in a newsgroup and then they yank my account, etc.

Ibid.
Will pass that tip on to them...

$14.95 a month paid to my ISP...
--


Regards,
Joe Agro, Jr.
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How tight tolerance is the drill bushing to the drill?
Mebbe machine the bottom of the bushing very flat, and have it press tightly against the material. God willing, there would then be no burr, or if there were, the burrs would be then so fragilely bound to the material that they could basically be wiped/air jetted off.
It might also be possible to have high-pressure air blowing down into the drill bushing, and driving back any emerging burr material into the hole, for shearing by the drill flutes. Proly be perty noisy, tho. Possibly a power washer-type ditty--noisy and messy as well.
The bushing could be drilled symmetrically for these jets of air/fluid, inside a roundish manifold type ditty with a hose/plumbing connection. Would also serve as coolant, perhaps. Perhaps keeping the operation cooler could help with the burrs, as well.
Could also time it so that the initial blast is for "re-inserting" the burr for shearing, then turned off so as not to interfere with chip removal. Coolant could then be turned on, since you have now have a manifold.
Speaking of shearing, mebbe an endmill ground with a drill point might have a better shot at shearing off the burr, with/without air, etc.
--
PV'd, Hack Machining Inc.

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