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dixdance
02-29-2008, 12:11 PM
I need to turn some 12" schedule 40 pvc pipe on the lathe. The stuff is so gooey I'm having trouble getting a good cut. Would appreciate any advice on tool geometry and speeds & feeds. Also, would any type of cutting fluid help?

Thanks, Richard

pcarpenter
02-29-2008, 12:17 PM
I've turned it with pretty good success. Do not look for a shine in the finish. The stuff turns very smoothly with the right tool, but the surface finish is matte.

You need to use HSS tooling, ground to a sharp edge but with a rounded nose profile. I found that tools I have made for use on aluminum for finishing have about the right architecture for turning PVC. Do not get in a hurry or the tool will grab. I turn dry. I can't imagine trying to deal with the rats-nest turnings you get with something wet all over them.

Paul

Oldbrock
02-29-2008, 12:17 PM
lots of top rake and lots of back rake and very sharp cutting edge. You will have lots of mean hay, flies all over the shop. Peter

kf2qd
02-29-2008, 12:20 PM
I concur on the sharp HSS tool The other thing that helps is having the hose from the shop vac right next to the tool to suck the swarf as it comes off thetool. Keeps it from winding around the part or the chuck and then cleaning the lathe for you...

Pete H
02-29-2008, 12:24 PM
Lots of rake, very sharp HSS edge, rounded end. Keep the speed low or the stuff will melt into a band, and then will gather the birdsnest into a big enough mess that it might grab the shank of the cutter.

The vacuum will help, but keep a grab-hook handy to pick off the strings - don't do it by hand, they're stronger than they look.

Pete in NJ

phatfred8
02-29-2008, 12:53 PM
I done a lot of turning in the plastic area in Delrin, PVC Fitting, and Urethane's. Like the other's have said, the positive top and back rake are the way to go with a nice radius on the nose. But to help with the strings of material raping I used my shop vac mounted off the wall. Once the the string floats around the vac will suck it up and collect it no matter the length. I was machining some delrin wheels for a customer, 150 pcs total and this made the job a lot easier. I did not have to stop every pass and remove strings. Worked Great. I did use ear plugs.

Hope this helps,

Brian

dixdance
02-29-2008, 01:07 PM
thanks for all the good tips guys, especially "chip" management. what a mess!

any thoughts on surface speed?

thanks, richard

dockrat
02-29-2008, 01:20 PM
I have had great success using a DCGX 3(2.5)1 AL H10 for turning and a CCGX AL H10 for boring in plastics of all kinds.They leave a great finish too. As was said above these are designed for aluminum. Had a he11 of a time before I tried these. I never thought of the shop vac thing though altho the strings just fly up over my shoulder and end up in a pile by my right foot. Not really a problem. generally I spin it around 900 RPM

Ernie

2ManyHobbies
02-29-2008, 01:58 PM
I've had luck with lower speeds, if it starts to heat, you get a real mess. I turned a shop vac adapter out of a piece of cutoff and a connector. Solvent welded the connector onto the piece of cutoff and let it stand for 24 hours. Then I faced the cutoff down to the edge of the connector, then came back with a boring bar. It might have been 600 RPM or so, though I'm not sure. I had tossed a previous piece of cutoff because it heated and deformed with a reciprocating saw. My next piece was cut with a hand saw and came out much cleaner...

winchman
02-29-2008, 02:21 PM
How are you going to support the pipe and hold it in the chuck?

The PVC pipe I've turned (it was 4" and smaller) had to have a tight-fitting plug inside the chucked end to keep it round.

Roger

Evan
02-29-2008, 03:48 PM
Soapy water is an excellent coolant for most plastics. It keeps it from melting which is the biggest cause of problems. And, you can easily get a nice shine on the parts when turning. The tip of the tool needs to be polished. I make all sorts of things from PVC pipe, especially optical systems and small telescopes.

DR
02-29-2008, 07:53 PM
Done lots and lots and lots of PVC pipe. We used to make water collector systems for an environmental consulting company.

Turn with a CCGT insert. (I think that's the designation) CCGT is an 80 degree diamond, high positive, polished insert. Plastics are hard on HSS, the carbide gives good life.

BTW, the CCGT's have an edge sharpness you'd be hard pressed to get with HSS.

As was mentioned, you need an internal plug to prevent distortion in the chuck or collet.

We run dry, fairly fast. Fast enough that the chip string is very soft from the heat. Chips are hot enough to burn your bare hands, wear groves. The insert geometry, speed and softness of the hot chips tend to shoot them off in a predictable direction (most of the time).


CCGT's are an excellent insert for plastics, wood, brass, aluminum, even finishing cuts in 300 series SS.

ulav8r
03-04-2008, 05:05 AM
I made several mandrels out of solid PVC rod at a previous job. Had a 16" SB, ran it on high speed. Mandrels were 1" to 3" diameter. Used a HSS bit with no top rake, 5-6 degree side rake, square corner, and a polish on all surfaces. Took light cuts at high feed rate by hand. Front of tool was 1/2" wide, cut a ribbon 1/2 inch wide and left a very smooth finish.