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madman
12-26-2008, 08:59 AM
6 inch clear pvc Pipe, Wow costs 79 dollars a foot? i wondered the best way to hold and machine it in the Mill. I dont want to scratch or crack it? perhaps a ??? aluminumn collar of sorts? thanx Mike

Carld
12-26-2008, 09:37 AM
Some info as to what your doing to it would help determine how to hold it.

madman
12-26-2008, 09:47 AM
Well im facing the ends to proper length and also machining some holes in the sides and a few small slots. thanx Mike

Bob Ford
12-26-2008, 09:58 AM
2 inch wide clear cellophane tape applied smoothly should protect the finish. The residue can be remove with wd 40.

Bob

Evan
12-26-2008, 11:26 AM
Mike, are you sure it's PVC and not acrylic? There is a big difference in the machining properties.

macona
12-26-2008, 04:19 PM
Yeah, clear PVC is spendy stuff. Practice on some normal PVC first. Keep your speeds down and feed up. Machines pretty easily. When drilling you want to use a drill for plastic or modify one to work. You want a negative rake drill. Search for drilling plastic for more info.

darryl
12-26-2008, 04:23 PM
It's always a challenge to keep something pristine looking when it has to undergo further machining operations. Keeping pipe round during clamping and machining is another challenge. Usually a collar of some kind will work to do both, and the tape is a good idea. Keep in mind that it's not a good idea to rely on the stiffness of the material to keep it tight with the clamping method. If the piece could possibly flex and thus loosen with a proposed method of clamping, then it's probably not how you should arrange to hold it for machining. As an example of this, consider a piece of pipe held in a three jaw. If you don't have a tight-fiting disc inside the pipe first, there's nothing to resist the clamping forces from the jaws except the rigidity of the material. It won't take much resistance from the cutting tool to flex the piece right out of the chuck. Especially plastic pipe- I've been lucky a few times that I didn't end up having the workpiece sticking out of my forehead.

If you're not sure of the material, and even if you are, it's a good idea to test on some scrap before committing the 'non-replaceable' piece to the cutters.

Carld
12-26-2008, 04:24 PM
For one thing, I think it would be best to make a wook plug and face it in the lathe. You could drill holes and mill slots using V blocks or clamp it to the table and the side of an angle plate or a large piece of angle iron. All you need to do is keep it from skooting around on the table.

Scishopguy
12-26-2008, 04:41 PM
Madman...The best way I have found to hold PVC or cast Acrylic tubing in a chuck (lathe or indexer on a mill) is to cut a circle of the thickest plywood you have, traced from the inside of the tube. You can wrap masking tape on the edge to protect the finish. This will give you a firm grip and keep the stuff round at the same time. If it is long then just cut two disks and drill a hole in the center for a piece of threaded rod that you can hold between centers. If you are working on the side of the tube, I have found that a piece of channel iron of the appropriate size ( for 6" I used a 4"x 2"x 2") that you can bolt to the table's t-slots. Then just use a strap clamp on either end. I used to repair Niskin Bottles, a type of sea water sampler, that were made of PVC pipe and had to clamp them on the mill and occasionally turn them on the lathe to reface the sealing surfaces on the ends.

Liger Zero
12-26-2008, 04:52 PM
For soft materials I put a wooden dowel inside and wrap the outside with a single layer of scotch-tape. Harder materials I just use the tape on the outside. It's a judgment call, what I consider "soft" and "hard" plastics differs considerably from what someone who machines metal considers "hard". :D