Advice needed - turning moldable materials: resins, plastics, composits, etc

[bkcabot]

I am in the process of searching for a material that can be injection molded, and then turned. The final product will need to be very rigid, and have the ability to be turned to a glass-like finish. I know a lot of people turn composites of various types (Corian, etc) - I think a lot of pen turners do this. Does anyone have any advice about materials that can be mixed and poured/injected into a mould, and then turned once dry? I would like for the product to be available in a variety of colors as well.

Thanks,
Ben

 

[Richard Baker]

Ben, You used the term "poured/injected". There is a world of difference between injection molding and simply casting a resinous material. Also a world of difference in the equipment required. If you are interested in a casting resin the folks on the penturning forums should be able to give some good advice.

 

[Steve Worcester]

Injection molding like in plastics, ABS and the like?

There are alot of products like resins that can be pressure cast and color added, but injection molding is a whole different thing. They do have clear ABS that will polish up real shiny and almost clear.

 

[Ed Davidson]

Ben,

There are lots of off-the shelf materials that might work. You might try cast acrylic rod - available in lots of diameters, up to 3", and in clear as well as opaque colors. Check out this link for prices and availability. If you want to cast your own stuff, polyester resin is the way to go. As was stated earlier, penturners.org has lots of tutorials on the stuff.

Here are a couple of yoyos turned from 2" diameter cast acrylic:

And here's a couple more from 2" diameter cast poly resin, imported from Europe:

 

[john lucas]

I would say Ed is the master at turning all sorts of Plastic sort of materials. I've turned quite a bit of different stuff. I find you have to play with speeds and how hard you push the tool. It tears out easily if you force the cut. Shear scraping works really good on some but not others.
Most plastics will sand to a very high polish but some are very heat sensitive. I've turned a fair amount of epoxy, Inlace, and some casting resins. All turn fairly well if you use sharp tools.

 

[squirrel]

Hello,


I tried to cast an epoxy bottom in a wooden ring of about 15 inches wide. The bottom bot thicker than 0,4 inches thick.
But it shrink too much although the good thing was that i really can polish it up as a mirror (which makes that the small holes in the surface were hidden.
I have the intention to adjust a bit of epoxy in the empty space (empty because the epoxy shrank away) and see if I can see where the two parts meet or if the borderline stays invisible.

As far as I understand acrylics are easier to turn than epoxy, is it not?
And do they shrink as much as epoxy do or not?
And with what kind of glue can different parts be glued together or can the acrylics be glued to wood?

Ok, I will go tot the penturners forum as well but I thought Ed knew the answer on this as well.

Thanks for the help!
Squirrel

 

[Joe Greiner]

Cooling shrinkage will be a problem with any cast material, even metals. That's why a shrinking allowance is added to most foundry patterns, and it's different for each material too. Polyester and epoxy resins are also sensitive to the volume of material, and each shape may need experimentation to establish catalyst proportions to prevent cracks during cure.

Almost anything can be added to the mix for added features. But be aware that turning will probably intersect them for good or ill, especially if you're preparing generic blanks; casting to near-final shape might not. Experimentation is advised here too.

As already mentioned, injection molding is an entirely different kettle of fish.

My spies report that Ben resides in an apartment. Available work space could also be a consideration - hobby vs. industrial level.

 

[Ed Davidson]

One of the 2009 symposium demonstrators uses epoxy extensively in her turnings - Marilyn Campbell - click on this link to go to her site. Perhaps you could pick up some how-to’s from one of Marilyn’s classes.

 

[squirrel]

Thanks a lot!
Yes, Marilyn's work is amazing!
I will write her and see what will be possible.
Best regards!
Squirrel

 

[john lucas]

I have found some things shrink and some don't. Contact the manufacturers to see how their product works. I use Clear Inlace and it does not shrink unless you put other materials in it (which I often do). Then it might shrink so it's a good idea to run a test.
The Cast -n-craft that I have used does not seem to shrink. I have just started experimenting with epoxy by West Systems and their literature says that it will shrink or expand depending on what you do to it. I mixed a lot of thickener with it and it almost doubled in size as it dried. It did shrink a tiny bit with nothing mixed in using the slow hardener.