How to machine poly urethane?

[colinag]

I need to replace some engine mount bushes for a racecar. They are no longer supplied by the makers. They are made of the same material that after market suspension bushes for performance cars are made from.It's that red stuff you can dig your finger nail into.I had a hard time finding the material to make new ones from here in the London On area and the seller did'nt have any advice .Can anyone help? Thanks in advance.

[Machinist-Guide]

Freeze it. If you freeze it it will get hard and machines much better

[Toolguy]

It's hard to keep it frozen long enough to do much. An easier way is to sand or grind it. You can use a toolpost grinder in the lathe or shape it freehand with an air or electric die grinder with sanding discs or drums, with the part turning in the lathe.

[lbhsbz]

Machine up a 2 piece negative and mold your own with material from McMaster..

[teejay]

We make test plugs out of it use high speed steel tools that are sharp and high rpm with light cuts

[old_mikee]

+1 for Casting a set. It may be less expensive than buying it in block form and machining.

Make a wood or aluminum mould base to size and press in hole sized pins where you want holes.... You can use cardboard and tape to make the 4 sides of the mold box.... Apply a spray release agent, mix and pour (level mold or casting table before pouring and make sure it will not leak) then pour to desired thickness.

There are several good choices for purchasing cast-able materials, and it is relatively easy to do.

Both http://www.silpak.com/ or www.smooth-on.com/ make quality easy to cast urethanes


mike

[big job]

We have been using hockey pucks for years body mounts flathead ford
engine mounts and they can be turned.

[paulsv]

Freezing does help, but it warms up quickly. On some small poly pieces I had to turn, I froze them, and then used canned air, which helped break up and blow away the stringy chips, and kept the workpiece cool. It really helped the machining. It was the kind of compressed air that comes out of the can quite cold.

I have also cast small gears from Poly. You have to be careful, tho, with Poly casting resin, that you get a casting mixture that has the hardness and strength and other properties you want. It was my understanding, from the little research I did, that some of the higher strength casting mixes require vaccum casting. But I'm far from an expert.

[paulsv]

By the way, Smooth-On has stocking distributors in pretty much every state. I found that there was one a few miles from my house. The people there were very expert and helpful in getting me the right resin for the job.

[old_mikee]

Actually, most urethanes can be mixed and poured without vacuuming...... Silicone rubber is veery viscous and traps air during mixing usually requiring de-airing in a vacuum chamber, but urethanes are pretty forgiving. (It is important to keep the A/B ratios accurate, either by weight or by volume)

mike