Nylon Bushings

[John3]

Can anyone give advice on CNC turning of Nylon 6/6?

We need to make bushings out of 1.25" ID x 1.75 OD Nylon tubing.

We will be boring steps in the ID, facing/turning one end with a 45 deg taper and doing cutoff.

We've made these before on a manual lathe with mixed results. It seems the operator must develop a skill for feeds, too slow and the material melts, too fast and we get bad finish or worse yet, the part grabs.

I wonder/worry how well our CNC lathe will develop this "feel" I'm looking for suggestions on speed, feed, tool geometry/material, coolants, etc.

Thanks in advance for any comment,

John

[big_mak]

Keep your tools sharp, and your parts cool. Especially if you are using a plug gage to check the ID. Ask me how I know. You won't have good luck breaking the chips. I'd say with a CNC you could try machining any diameters in a peck type of technique to keep the chips as short as possible to avoid pulling your coolant nozzles all over the place.

I'd say use cutting tools designed for aluminum, as you are gonna want to cut this stuff, and not try and lob it off.

[Geof]

As suggested use micrograin carbide positive rake tooling; you want to slice the nylon off. Speed should be about half what you would use for aluminum, maybe less, but feed should be possibly double.

Use the G74, G75 cycles with a very short peck distance to try and break off the chips. It adds time but it might save you having to insert program stops to untangle things.

[John3]

As far as keeping the stuff cool. I know that's critical, but we've always tried to keep it dry because of dimensional stability.

We've seen nylon shrink and grow (sometimes out of spec!) depending on the moisture content.

We've avoided water based coolants like the plague.

Therefore we've used things like air jets and those vortex coolers.

Any comments?

John

[Geof]

.....We've seen nylon shrink and grow (sometimes out of spec!) depending on the moisture content.....Any comments?

John

Yes, I think plain nylon can grow several percent depending on moisture content and just about any liquid will soak into it.

The trick is to try and get good chips that come clear; a healthy DOC and feed will mean most of the heat from the cutting gets carried away in the chip. It is just tricky balancing heavy cuts and distortion of the material to get parts within spec as it is practically impossible to take a cut of a few thou if the size is just over.