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MattMaier
03-01-2015, 12:21 PM
I'm planning a project that will require me to do deep hole drilling in acetal plastic. Owing that acetal is a thermoplastic, I know that if I'm not careful, I can overheat the part and cause it to melt. What is an effective coolant to use on acetal that would be available to a home shop guy like myself?

peekaboobus
03-01-2015, 12:54 PM
I just use water and detergent.

Melting has never been a problem. It cuts pretty well. Now, if you are cutting acrylic, that you have to watch out for melting. I've never had acetal or delrin melt on me.

Carm
03-01-2015, 01:08 PM
Compressed air, cold gun if you have it.
Watch out if you have tolerance you need to hit, it is a bit hygroscopic and can have thermal variation; measure at room temp. or at design temp.

Black_Moons
03-01-2015, 01:13 PM
Biggest protip: Let your drill bit cool!

If your REALLY smart, you'll grind back the flutes that are more then 2 or 3 diameters behind the tip of your drill, Massively reduce side rubbing. Have not done acetal but have done acrylic dry. Needed to use VERY low rpm and let the drill bit cool between several peckings. Once went too fast, VERY ugly hole.

Keep the drill bit cool to the touch. If its not cool, your hole isent either.

peekaboobus
03-01-2015, 03:35 PM
Basically you know when you are cutting delrin too hot. It smells like crap. It literally smells like rotten fish. That tells you right away you're cutting it a little hot. Also, those vapors are probably obviously not good for you. So lots of ventilation.

bobm4360
03-01-2015, 04:27 PM
Compressed air, and withdraw the drill completely every 1/4 inch or so. I've drilled acetal at the same speeds used for aluminum. Experiment with scrap pieces to find what works best for your setup.
Regards,
Bob

MattMaier
03-01-2015, 09:37 PM
Well, it isn't a machine part I'm making for one. It's actually a musical instrument, much like an oboe, of which many low cost oboes for students are made of delrin.

Toolguy
03-02-2015, 12:32 PM
Use a parabolic flute drill. Those are made for deep hole drilling. They cause less friction and move the chips efficiently. They do not start well. It's best to start with a spot drill or short drill of the same size for a short bit. Then the parabolic drill will be on location and go fine from there. All the above still applies.

Carm
03-02-2015, 01:14 PM
Well, another thought since I see problems drilling that long.
Can you make two sides and chase the hole with a ball end mill or a router core box bit?
ISTR that acetal doesn't glue well, you'd have to make binding rings, could be a design feature.

Another possibility is making a clarinet reamer, where one can't afford to have a breakout hole in expensive rare wood. Slow going, but not particularly hard. Sort of a gun drill from the 18th century.

Glug
03-02-2015, 02:30 PM
Have you considered a drill bit with coolant passages?

Black_Moons
03-03-2015, 03:56 AM
Compressed air, and withdraw the drill completely every 1/4 inch or so. I've drilled acetal at the same speeds used for aluminum. Experiment with scrap pieces to find what works best for your setup.
Regards,
Bob

I find aluminum speeds wayy too fast, Yes you can drill a little faster at higher RPM but in a deep hole the side rubbing will bite you at higher RPM's with plastics.

Also, When suggesting a length related to a drill operation, its best to speak in drill diameters and not inches. 1/4" peck distance makes perfect sense for a 1/8" to 1/4" drill bit. Not so much for a 1" drill bit. 1 or 2 diameters deep makes sense for any size drill bit.

elf
03-03-2015, 12:22 PM
Another option would be to form it using this technique: http://bbs.homeshopmachinist.net/showthread.php?t=43645 This would allow you to easily create different size bores.

MattMaier
03-05-2015, 10:12 PM
All the suggestions for tooling are welcome, but I have to do this on a budget, ergo I'll be having to make my own tools, reamers and D-bit drills and such. Also the plastic instrument is a prototype so I can work the method of construction out, then I'll have a go at it in wood.