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Saturday, August 7, 2010

Turning a Tru-stone Pen.

My son's pen turning interests have persisted, and here he's turning a material called Tru-Stone. This material is advertised as being made of powdered stone mixed with "gem" resin. Judging from the smell it gives off while turning, it's a polyester resin similar to what's used for laying up fiberglass. If you read the instructions and warnings on the web sites where this stuff is sold, it's promoted as being difficult to turn, harder than other materials, requires super sharp tools, etc. Our experience is that brazed carbide tools like it. Zip through it like butter while making a nice sizzling sound, in fact. It does tend to chip when first rounding the square blank if you hogg off to much material at once. We turned it with a spindle speed of 1000 rpm, using a 60 degree tool of the sort usually used for threading. The point of the tool was given a smallish radius like you might use on a finishing tool. This worked just fine, could cut in either direction while roughing, and gave a nice smooth finish. In the photo you can see chips from the material flying off the point of the tool. It's sort of fun to take photos of stuff flying around while someone else operates the machinery. I've always wanted to Direct. The swarf this stuff makes is just awful. It's a coarse powder that has a static charge, and clings to you, the lathe, and everything else, like Styrofoam beads, except smaller. Sanding and polishing is the same as with acrylic materials; 400 grit, followed by 600 grit, followed by white rubbing compound. It is harder to polish than the acrylic, and a lot less forgiving where fine scratches are concerned. It also make lots of fine dust, which we have been breathing with reckless abandon. We'll probably grow antlers or something as a result. Once polished, it looks even better than the acrylic. I have some other polishing compounds that I want to try, left over from decades ago when I did some metal polishing, but they're salted away in the attic, and I've been too lazy to hunt them down in the heat. I've got to get up there and find the box they're in. The finished pen is ostensibly of Persian Turquoise, with brushed chrome hardware. It's resting on a piece of Tru-Stone Malachite, destined soon to be another pen. It's been turned round and polished, just to see what it will look like. I personally like the looks of the Malachite a lot better than the Turquoise. You may have gathered that I have my doubts about the composition of the Tru-Stone material. I'm having a hard time believing that it's really made out of powdered stone, particularly considering the ease with which it's worked. But, that's what the people selling it and, I assume, the people manufacturing it claim, and I have no reason to doubt their veracity, other than my natural skepticism, which I've been told is extensive. I would like to see how it's made, though. One last comment. The Tru-Stone feels warm in your hand compared to the acrylic, which, to me anyway, feels cool to the touch. It's also considerably heavier. Hey, it's made out of real stone!

Update: GoatRider has sent a photo of his latest creation. Marble Tru-Stone, it is. Nice looking, too. As always, click to embiggen.

7 comments:

smellsofbikes said...

I've used stuff like that before. It's pretty much what you're talking about: chips of stone in resin. They also make reconstituted opal gemstone the same way.
If you're going to be turning a lot, I'd advise hooking a household vacuum cleaner up with the nozzle attached to the toolpost while you're turning: all the junk goes away. The swarf is filled with what's basically sand, so keeping it away from the lathe ways is probably a good idea.

Smitty said...

Ya know, the vacuum hose mounted to the saddle on some sort of an adjustable mount is a good idea, and something I should have tried a long time ago, not just for acrylic, and Tru-Stone, but other plastics. My shop vac and it's hose are twenty years old and held together with duct tape. Maybe I can wrangle a new and longer hose for Christmas. If you have a source for that opal based material you're talking about, or can find one and pass it on, I'd like to have it. It has to be pretty expensive. I've bought Opal in the distant past and recently. I was dumbstruck at the change in price over the years.

GoatRider said...
This comment has been removed by the author.
GoatRider said...

I just turned one of these, the "Leopard Skin Jasper" version. I had a heck of a time turning it with a skew like I do with Acrylics. I tried different lathe gouges with little success. I did make a scraper work ok, but it was hard to control.
I have a Taig lathe, which is a mini machine lathe that I put a tool rest on. So I put the carriage on, and shaped a tool like a scraper, and that worked pretty good. It worked even better if I kept it wet, which keeps the plastic cool, and also keeps the dust out of the air. I wet sanded also.
Unfortunately, I was turning a Eurostyle pen, and it shattered when it got too thin. I think next time I'll do a straight-sided American style pen.

Smitty said...

My understanding is that Jasper is one of the harder types of Tru-Stone. I haven't tried turning jasper myself. The hardest Tru-Stone I've turned was Lapis. It was very prone to chipping, and required making very shallow passes, and was hard to polish. I never achieved the level of finish that I wanted. Oh, well. There's a lot of stuff out there that's easier to turn, and appeals more to my tastes. Sorry you destroyed a blank. The American style pens do have thicker sections, and should be less likely to split out.

GoatRider said...

I just turned a "White Marble" Trustone pen, and it was WAAAY easier than the jasper. I was able to ride the bevel with my skew as I do with acrylic, just having to sharpen a little more often.
Thanks for your help!

Smitty said...

Thanks for your comments! Send me a photo of your pen if you're so inclined and I'll publish it.