Urethane Milling

mmaughan · May 26, 2021

Hey all,

I have never milled Urethane before. I was hoping people with experience could help me figure out the ins and outs of cutting a square stock of Durometer 90A.
Like:
1) How tight I can clamp the stock in a vise without deforming my end result too much?
2) Coolant or no?
3) Feeds and speeds?
4) Anything else to keep in mind?
I'm using a Sharp SV-4020 Vertical Milling Center.

Milland · May 26, 2021

90A is fairly hard, but you could squeeze it too much if you're not careful.

You can try cleaning your vice jaws carefully, and 2-sided taping some course (180 or so) sandpaper to both faces to help with grip. Cutting dry with sharp carbide tools would be my start, but you'll have to figure out what parameters work for you. Air blast next, coolant as a last resort due to mess factor.

mmaughan · May 26, 2021

I have a torque handle I can use. Thanks for the tip with the sandpaper.

FredC · May 26, 2021

Milland said:
90A is fairly hard, but you could squeeze it too much if you're not careful.

You can try cleaning your vice jaws carefully, and 2-sided taping some course (180 or so) sandpaper to both faces to help with grip. Cutting dry with sharp carbide tools would be my start, but you'll have to figure out what parameters work for you. Air blast next, coolant as a last resort due to mess factor.

Cold air blast from a vortex tube is very helpful. We did some lathe work on urethane and waiting till the part turned white with frost before hitting cycle start got us through what was a very difficult job.

mmaughan · May 26, 2021

FredC said:
Cold air blast from a vortex tube is very helpful. We did some lathe work on urethane and waiting till the part turned white with frost before hitting cycle start got us through what was a very difficult job.

I don't have that kind of equipment.

BoxcarPete · May 26, 2021

+1 to keeping it cold, but the more important thing is to keep consistent. If you must hold it in a vise, it will be deformed. Cold increases hardness of rubber, which can help you cut it and reduce deformation. But, if the temp is all over the place the variation will go up.

I don't know what kind of stock removal you intend to do, but grinding is a viable option.

FredC · May 26, 2021

mmaughan said:
I don't have that kind of equipment.

If you have an air compressor you have finished half the battle, Vortex tubes are cheap and trouble free. I tried putting the parts in dry ice and alcohol but the 1/4 material warmed up too fast even when it was below zero when you pulled it out of the solution.

mmaughan · May 26, 2021

BoxcarPete said:
+1 to keeping it cold, but the more important thing is to keep consistent. If you must hold it in a vise, it will be deformed. Cold increases hardness of rubber, which can help you cut it and reduce deformation. But, if the temp is all over the place the variation will go up.

I don't know what kind of stock removal you intend to do, but grinding is a viable option.

I plan on taking off 0.020 per pass.

This is for a Brake Press Die.

stephen thomas · May 26, 2021

Can you grind it?

I spin grind some rubber parts, softer than 90 Duro A.

I use mist coolant for lube, 36 or 46 wheels.
Goes pretty fast.
Any "grip" will distort it. Just have to figure how much is acceptable & in what direction.

smt

crazygoat · May 26, 2021

Put it in your freezer over night and then grind it. This has worked for me in the past.

BoxcarPete · May 26, 2021

Another thing to consider for holding: rather than using a torque wrench, it might be better to make a hard stop from steel, at a slightly smaller dimension than the stock. Just tighten down till the jaws stop moving and it will be much more consistent. I'd start with about 98% of your holding dimension and adjust down from there if you think you need it for more grip.

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