Machining polycarbonate

Are there certain cutting fluids which shouldn't be used on polycarbonate? MSHA only accepts non-aromatic, water or water-soluble oils. Anyone know anything about this or know any resources which will point me in the right direction?

You shouldn't need a cutting fluid to machine polycarbonate.

You shouldn't need a cutting fluid to machine it. What are you going to use it for? The glass transition is around 150 C and the melting point is around 267 C, so you shouldn't need to worry about the blade getting hot enough to anneal it or something. I don't see why water wouldn't work if you were very worried about it.

I am not machining. Basically we have a polycarbonate tube 10" long machined with an ID of 1.812" and OD of 2.375" as well as having 2 1/8-12 UNJ thread cut on one end. Someone was trying to blame the cutting fluid as causing a number of the tubes to break by a chemical reaction between the cutting fluid and polycarbonate weakening the polycarbonate. However the cutting fluid that is being used on them is a water soluble fluid.

So this happened well after the machining or during it?

You do have to be careful working with plastics because of the melting. The plastic melts and the hardens around the bit, locking it up, then the bit snaps off. When drilling at least, you have to use low rims to keep this from happening.

I would blame the machining itself, not any sort of cutting fluid. I have done plenty of analysis here on polycarbonate, polysulfone, radel, etc. machined plastic parts that later develop cracks due to machining stresses. Especially if any threads are cut into them.

93EXCivic wrote: I am not machining. Basically we have a polycarbonate tube 10" long machined with an ID of 1.812" and OD of 2.375" as well as having 2 1/8-12 UNJ thread cut on one end. Someone was trying to blame the cutting fluid as causing a number of the tubes to break by a chemical reaction between the cutting fluid and polycarbonate weakening the polycarbonate. However the cutting fluid that is being used on them is a water soluble fluid.

You should be able to send it to your lab and have them find out. It would probably be as simple as running an FTIR, DSC, and TGA. These tests will point you in the right direction. It's entirely possible that the resin used to make the tubes was wet or something. You didn't make a bad run, did you?

93EXCivic wrote: I am not machining. Basically we have a polycarbonate tube 10" long machined with an ID of 1.812" and OD of 2.375" as well as having 2 1/8-12 UNJ thread cut on one end. Someone was trying to blame the cutting fluid as causing a number of the tubes to break by a chemical reaction between the cutting fluid and polycarbonate weakening the polycarbonate. However the cutting fluid that is being used on them is a water soluble fluid.

This is entirely possible. At work (grinding company), we occasionally grind various types of plastics. One job - dunno exactly what kind of plastic - caused grief, due to microscopic cracking. After some researching, we found a machining fluid that worked, without causing the cracking.

ProDarwin wrote: I would blame the machining itself, not any sort of cutting fluid. I have done plenty of analysis here on polycarbonate, polysulfone, radel, etc. machined plastic parts that later develop cracks due to machining stresses. Especially if any threads are cut into them.

We just did a test with two polycarbonate tubes. They are both from the same batch of material and cut on the same machine. One was much weaker then the other...

How can I tell if a cutting fluid is aromatic or non-aromatic?

Sniff.

Petroleum will make PC brittle. The sharper the cutter the better it cuts and the less need for any coolant. If you do find you need some straight water works fine. Plastic doesn't absorb heat well most of the heat goes into the cutter so keep the part and cutter cool. Heat will throw any tight tolerances you are trying to keep out the window too.

93EXCivic wrote:

ProDarwin wrote: I would blame the machining itself, not any sort of cutting fluid. I have done plenty of analysis here on polycarbonate, polysulfone, radel, etc. machined plastic parts that later develop cracks due to machining stresses. Especially if any threads are cut into them.

We just did a test with two polycarbonate tubes. They are both from the same batch of material and cut on the same machine. One was much weaker then the other... How can I tell if a cutting fluid is aromatic or non-aromatic?

Did you guys extrude these or just buy some rolls of tubing?

In reply to rotard:

They are initially molded and then a final pass is done on the ID and the threads are cut.

RXBeetle wrote: Petroleum will make PC brittle. The sharper the cutter the better it cuts and the less need for any coolant. If you do find you need some straight water works fine. Plastic doesn't absorb heat well most of the heat goes into the cutter so keep the part and cutter cool. Heat will throw any tight tolerances you are trying to keep out the window too.

According to the website the cutting fluid is a water soluble fluid (Flexilube Biokool J). We are already having a lot of problems with the threads being out of tolerance but the machine shop that has been doing this is in South Africa because that is where we do a lot of our business.

I don't use any cutting fluid at all with polycarb. Just a air blast to keep it from melting and to keep the chips from binding.