facing plastic rod

Ive basically learn to use a lathe machining uhwmpe and stainless 316 not the best to learn on , Ive found hdpe acetel and delrin are easy to machine but uhwmpe is not very forgiving one mistake and it all goes wrong pulls out of the chuck as so slippy tools will dive in pulling it out of the chuck as well.No swarf sometimes facing you just get one big lump of goo forming .

Should have looked at the ARC advert at the beginning of the mag, that nice man Ketan has written left and Right on the tools in the pic

Luglord, how much material do you have sticking out of the chuck and what sort of dia are you working on, that pic of the white plastic being machined may have too much projection.

+1 for plastics not being best to learn on. Some are OK, many are horrible.

That lump of goo may indicate overheating due to your tool rubbing rather than cutting. Try a much sharper tool, more like a knife than the types we use on metal, and/or drastically reduce the spindle speed.

Not sure about suitable coolants for plastic, perhaps someone else knows?

Dave

Lug lord, one of the advantages of the 6mm diameter button inserts mentioned earlier is that they have quite a high positive rake which helps when cutting plastics and also worked quite well on some 316L stainless as I was working with recently. The problem with fast removal rates on plastic is that unlike metal it does not transfer heat into the material the way metals do. If the heat is not removed with the swarf then the surface of the plastic material heats up rapidly. I was cutting the nylon pulleys (photo in the earlier post) with a depth of cut of 0.5mm and a tool travelling at 100mm/minute. I think the RPM was about 500. The largest diameter on the pulleys is 85mm. If you are moving the tool slower than this with a higher RPM then you will get local heating which will result in molten plastic at the cutting point.

Martin C

All the variants of polyethylene have a very low melting point so are difficult to machine. All cutting produces heat so you need to use a very sharp tool and a low speed to minimise it. Possibly a flood coolant as well.

Russell

Air is probably the best for cooling. My experience is mainly in Nylon, a good sharp HSS tool, and not too fast, and clear the cuttings away as you go or it gets all tangled.

Ian S C

My preference for all plastics is zero or negative rake on the tool - this will certainly prevent digging in and pulling the work from the chuck.

In order to prevent the continuous ribbons of swarf from tangling, I've never found a way of breaking this with the tool, I used high speeds and threw the swarf as a continuous ribbon into the air and clear of work and machine.

Nigel

this is how i have always faced plastic off with the carriage locked so no movement

For the one in the drawing above to work as a facing tool it needs the top rake in the opposite direction to the R/H Turning tool you opened the thread with.

The carbide tips have rake in both directions that is why you have had good results using the insert in a R/H holder.

Edited By JasonB on 28/11/2017 19:32:55

after a re grind using an eclipse 5/16 hss finally it works a treat now