[martinw]

Dear All,

I need to put a large number of 1/2 inch diameter holes in the sides of polycarbonate electronic enclosures. The holes will be tapped to take cable glands afterwards.

The boxes are about 10" wide, 6" tall, and 3" deep. The wall thickness is about 3/16". I can drill the holes with the box lid on, so this will increase rigidity while I plunge with the drill bit.

Drilling plastics has always given me some grief in the past, so I tried using a Forstner wood bit. It seems to work really well.

Could anybody suggest if I need some kind of cutting fluid while drilling to increase the bit life, and to leave a smoother finish in the polycarbonate?



Thank-you,

Best wishes

Martin

[teamtexas]

I've used Forstners to drill PVC and ABS plastics on a regular basis. Keep your speed down to a few hundred rpms and your bit should last for a long time. If you use to much speed it will cause the bit to heat and create a burned rough finish. You can use water to cool the bit if needed.

Dan

[under-dog]

I worked at a display company and we used twist drills but they had a much more severe angle on the tip(not sure of the actual degree) and the tips were "dubbed". The cutting surface is ground perpendicular to the axis of revolution. This way the bit scrapes the hole rather that twist into the hole and coil out material like it does on metal or wood.

Plastic grabs bits and sucks them in and poly carb is fairly gummy.

Check out this link and download the PDF on the first result. This is on my old companies site and it is a PDF from GE about how to process thier plastics.


http://sitesearch.gigablast.com/sear...how+to+acrylic

[IQChallenged]

I surprised you're happy with the Forstner bit. But if it suits you that's all that matters. If you decide that the holes are too rough you will find the answer in using bits made especially for acrylic (aka Plexiglas) and poly. One place to get them is Tap Plastics. (Do a Google search). I've been buying from them for years. The bits made for plastics are noticeably different. The points are longer as a result of using a different angle. It really makes a difference. I'd do a few hole in scrap to decide which RPM works best for you. But no matter what you do you'll get a nice clean hole with no melting like the Forstner. I don't use any coolant but I do drill in spurts to keep the heat down. Soapy water might be good. I usually do a slight touch with a countersink to finish them off. Working with some scrap will help you find just the right combination but the special bits is what really makes the difference.

[martinw]

Dear teamtexas, under-dog, and IQChallenged,

Thanks so much for your lightning replies.

Obviously, there are better ways to tackle the problem, but we live in an imperfect world (LOL).

I will keep the revs down.

As regards a water cutting fluid, I did actually improvise at about 7pm this evening with the remains of my cup of coffee. No detectable improvement.

Thanks guys,

Best wishes

Martin

[fatal-exception]

I've used 1/2" center cutting endmills to succeessfully drill polycard for the last few years. Just make sure the job is held tight.

I've read somewhere that soapy water makes a good lubricant. Never tried it myself...

Paul

[vger]

You might try a 1/2" counterbore bit with a pilot drill in place of the pilot shaft.

Steve

[brunog]

Martin,
I've allways had good results with "Unibit" type multistep drill bit, these bits are excellent in making hole in thin material: plastics, sheet metal, electric emclosures, metalic stuuds, etc...

What I also like about them is that 1 single bit can cut many hole diameters and finish a hole with a chamfer.

Best regards

Bruno

[martinw]

Martin,
I've allways had good results with "Unibit" type multistep drill bit, these bits are excellent in making hole in thin material: plastics, sheet metal, electric emclosures, metalic stuuds, etc...

What I also like about them is that 1 single bit can cut many hole diameters and finish a hole with a chamfer.

Best regards

Bruno

Dear Bruno,

Yeah, I know the type, but I've never owed one. I've used "conecuts" in the past and have had ghastly results on almost all materials. Plastics especially. Probably due my ignorance...

Maybe step drills are the way, or end boring mill cutters, counterbores or whatever. The reason I'm thinking of the Forster bit right now is that I had such a wonderful cut into Delrin with it. One continuous paper-thin thread of swarf in a two inch deep hole. Beautiful sight. (OK, that makes me pretty sad, doesn't it!)

Well, the Forstner seems OK on a scrap polycarbonate box that was lying around. My coffee lube probably skated off the surface pretty fast, so I'll try a water cutting fluid with a plasticene dam. That way there is no chance of the bit heating up.

I came across this document about machining Lexan. I do not know if moulded polycarbonate has the same machining requirements. I hope it might of use to other people. It suggests that water or air are good coolants.

http://www.theplasticshop.co.uk/plas...sing_guide.pdf

Best wishes to all posters,

Martin

[mark c]

Just my 2 cents,
We do some polycarb where I work. Generally you want a low RPM and a feedrate that seems high and peck-drill it. Dubbing the drill would be good too. We mostly do smaller holes, though and the operator applies coolant (or water) from a spray bottle. I think maybe the way to go is drilling smaller, maybe .312" or so then follow with a .500" end mill and get some coolant on it anyway possible.
Hope this helps

[martinw]

Dear mark c,

Thanks, I will look up what "dubbing" means. Probably something to do with re-grinding a HSS bit.. ahhhhrggggg, no good at that.

Best wishes,

Martin