Working in Plastic and Small Holes...

Posting this here in case we have a plastic guru incognito...
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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Can they mount a small microplane type surface to the bushing and offset the bushing by the depth of the microplane?
-Nathan
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I think I understand what you are saying... However, the bushing guides the drill. It doesn't spin.
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Regards,
Joe Agro, Jr.
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Joe AutoDrill wrote:

I'm not a plastic guru (incognito or otherwise) but I solved that problem by switching to a (carbide) lipped brad-point bit.
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Morris Dovey
DeSoto Solar
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Do they make carbide tipped, brad point bits at the 0.029" size?
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Regards,
Joe Agro, Jr.
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Joe AutoDrill wrote:

You're closer to the sources than I am, and I did warn that I'm not a guru. :-)
My understanding is that with the right grinding setup it's possible to re-grind the business-end of an ordinary twist drill into that configuration. I'll guess that it might be possible with a carbide end mill as well.
The Lee Valley catalog used to have a decent photo of the end of a lipped brad-point bit tip - which might be a decent guide for a shop with precision grinding capability. I haven't received a catalog for long enough to know if the photo is still there, but my recollection is that it didn't look like rocket surgery.
--
Morris Dovey
DeSoto Solar
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First, I didn't mean my question as a flame so if it came across as one, please forgive me...
Second... Someone else suggested almost the same idea... I'll provide the information to the customer and let *them* try to find the tooling. :)
I know that sounds like bad business, but one thing is clear when I sell a tool... I sell the drill, but there are sooooo many variables on the tooling that I usually shy away from all but the most basic advice unless I have hands on experience.
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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"Joe AutoDrill" wrote:

Don't know if they are still in business, but if they are, one of my old time customers, Cleveland Twist Drill, could probably help you.
Lew
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I'm not a guru of anything but it sounds to me like the plastic is melting. The entry point bears the brunt because the drill bit is in contact with it the longest. I have no clue what they're trying to do but 10k rpm sounds like a lot for any drill. In fact I have never encountered a drill rated for that speed. Never looked but if I had seen something like that I would likely have noticed.
Something with a shank smaller than the hole would solve the problem if my guess is even remotely close.
Larry
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See: http://www.multi-drill.com/drill-speed-chart.htm
We don't show any smaller than 1/16" hole size, but the math can be done / estimated, etc.
CLIP
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Joe Agro, Jr.
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Plexi drill mandatory with 82 degree negative rake. Speed sounds excessive but must be acceptable. Would press drill bushing all the way through its substrate to entry surface of work. Templet must be clamped, of course. Change drill often. I would not expext hss to last long at these speeds.
Routs & drills all day: http://www.patwarner.com *****************************************************************************

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Speed should be okay, if not a bit slow IMHO.
See: http://www.multi-drill.com/drill-speed-chart.htm
We don't show any smaller than 1/16" hole size, but the math can be done / estimated, etc.
--


Regards,
Joe Agro, Jr.
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It sounds as though the bit is mushrooming the soft material as it enters.
Tell them to try a tapered bit.

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