Machining CM-70 clay

[JohnG]

Anyone ever machine CM-70 clay with their CNC machine? I'd like to know if it can be machined decent enough without it sticking to the mill bit before spending the $50-70 on the clay. From what I've read, the auto industry uses it to make prototypes.

And I like the idea that I can reuse it by just heating it up and reshaping it. And that I can smooth the surface out with just water if need be. Seems better suited for what I'm looking to do intead of dealing with machinable wax.

Here's more info on the clay: http://www.chavant.com/files/tech/gdti_13.htm

[JohnG]

Anyone?

[Splint]

Hi John,
I'm not sure if CM-70 is used but I know that synthetic clay is used by automotive design studios and that it can be milled. The spindle speed is usually somewhere around 1000 rpm, I think you would need to use a two flute cutter so the tool dose not clog up, you possibly may even have to polish the cutter with some type of wax so the clay dose not stick to it. The feed rate should be somewhere around 50ipm.
After machining home made scrapers can be used to smooth out any machining marks, I've never seen water used to smoth synthetic clay. If you keep it clean and dont get any dust and dirt mixed in with it you can warm it up and melt it to recycle it, be careful how much heat you apply, a flame will cause it to buble up and react making it unusable. You should be able to get a pretty good finish on it.

Hope this helps.
Splint

[JohnG]

Thanks for your input Splint.

Do you think running at 8000 rpm will work as well? My router can only drop this low.

[miljnor]

Ive actually done work for some car studio's and they use Ren-shape to mill (bondo like substance) and after milling the add clay in a really thin layer to the outside to get a *****en finish.

don't know what kind of clay it was but it never realy hardens and chances are it wont mill. It will probably just smear.

If you have a design studio around you they usually throw away alot of the used stuff. You could probably get a small amount and try to mill it.

[Splint]

8000rpm may work but it will probably overheat and smear, perhaps you could increase he feed rate and it may be ok. Miljnor has a good point, see if you can get a product sample and test it.

Splint

[Geof]

I had a look at the link and found this comment on the page; "The surface and corners of CM-70 can be smoothed nicely by hand at room temperature, although the flexibility is greatly reduced at room temperature. It would be difficult to take a cube of CM-70 and roll it into a ball at room temperature."

If you can smooth surfaces and corners by hand at room temperature I think it is way too soft for machining. Maybe if you took the temperature a fair way down. According to the information in the link it gets very formable at 145 degrees F so maybe if you could go down to around 35 degrees F it would be rigid enough to machine. Not really practical unless you had a real big walk in cooler.

[Splint]

They clay I have seen machined can also be smoothed by hand at room temperature. The surface needs to be smoothed after machining, only a very thin layer (perhaps 1 or 2mm) is effected by the smoothing, it's actually extremly hard (at room temp.) to drive your finger into the clay and make an indent of a significant size. I can't coment on the CM-70 as I dont know if is the same as the clay I have seen but it sounds like it has very similar properties. Keep in mind that the clay used in design studios can be machined and hand finished to a surface finish identicle to that of a pressed steel panel. Years ago pattern makers would hand make a clay model of a car and then a large gantry style digitizer would use the model to generate a cad file and from that dies would be machined, now days it works in reverse, cad files are used to make the clay models.

Cheers
Splint

[JohnG]

It looks as though clay is more of a hassle then what it's worth. I then looked up Ren-shape boards and came across this website: http://www.freemansupply.com/RenShapeModelingan.htm

This stuff would be perfect except it's expensive. I got quotes for the 5025($210) & 5030($300) boards. I think I'll have some of the other boards quoted since the difference between the two was almost $100. If the price is still high then I guess I'm back to machinable wax.

[Geof]

This thread mentioned making your own machinable wax.

Homemade plastic recycling?