Carving Rotary Lithopanes in 4” Inside Diameter PVC pipe (4 ½” Outside Diameter)

[200k]

The short version: You physically can’t do it.

NEW IMPORTANT EDIT 10/16/15: The short version: You CAN do it but you have to modify the LHR jig and fool the software. See entry #14 for detail on how it’s done! Of course you can read all the other entries before that to gain all the pithy comments, witty remarks, and wise advice that led up to it.

Back to the original post....

The long version: (with explanation, trial, and alternate ways of doing approximately the same of thing)

When I first saw the LHR rotary jig I thought, “What a great thing to carve PVC pipe on!” Schedule 40 PVC pipe is about ¼” thick, it is not brittle and though it will get pliable with heat, it will not melt easily and form the malignant little plastic balls like polycarbonate (Lexan) does that cripple the machine when they get thrown off the spindle by centrifugal force into assorted critical parts. A polycarbonate carve also looks like it was done with a soldering iron (don’t ask me how I know all this). Anyway, since the machine has a 5” max height for the Z axis and the jig has a max carve height of 4 ¼”, I thought 4” PVC would be a great medium. I thought about it for several months and then I went to the CW Conference 2014 and blown away when I saw Michael’s Mona Lisa carved in 3” PVC. I asked him why he didn’t use 4” and he reminded me (I already knew it, but I just didn’t think about it) that 4” PVC is actually 4 ½” outside diameter just like 3” PVC has an outside diameter of 3 ½”. Since the jig and software only take a maximum of 4 ¼” diameter, this pretty much ruled out 4” PVC as a medium.

But sometimes things get stuck on your mind and I kept thinking about how to jury rig or shoehorn in a 4 ½” diameter rotary project. I looked at all the jigs that people have made and posted on the Forum and had several in depth PMs with Dan Bergerud on how to fool the machine into letting the jig do it without the machine knowing it was doing it. We did come up with a way to fool the software – I say “we” but I really mean Dan thought of it and I agreed to it. So I made some end plugs for 4” PVC using Designer (it carves in 7-8 minutes) and rigged up a 7” long piece of 4” PVC in the rotary jig. (1^st JPG). I put it in the machine, cranked it down, and checked things. The bottom of the cylinder was clear (2^nd JPG) but the top of the cylinder was pressed on the bottom of the Z truck. (see 3^rd JPG) I couldn’t tell if the crank/head pressure was greater on the rollers or the PVC cylinder/z-truck but I know it was at working pressure. I could manually traverse the z-truck but it embossed a groove in the PVC. (4^th JPG)
Hmmmmmmm, this would not work. There’s no way the jig would rotate the PVC while the z-truck was dragging across it, not to mention the stress on the z-truck motor and gearing. It just won’t work. There is physically not enough room to put a 4 ½” tube, or cylinder in the Rotary Jig and have the CW machine carve it.

So… Ways of doing something like carving 4” PVC without actually doing it:

1. Carve 3” PVC. It works. We know it and plenty of us have done very nice things with it. The diameter is smaller so the curvature is tighter but if you limit your carve to about 1/3 the diameter the picture won’t get too much cylindrical distortion.
2. Carve 4” PVC – but first you have to cut and remove a strip .0785398” wide along the length of the tube and then cement the sides together again (and then get the whole thing ROUND again). This produces a tubing outside diameter of 4 ¼” which is within the limits of the machine.
3. Carve your lithopane on Corian and then use thermoforming (heat molding) to form an arc or circle if it has a large enough diameter. According to this PDF document: http://www2.dupont.com/Surfaces/en_U...mingCorian.pdf the minimum inside radius for thermoforming 6mm (¼”) thick Corian is 1” so a 4” inside diameter should be a “piece of cake”. Yeah, right. I’ve done thermoforming and it’s not really hard but it ain’t easy either. (last JPG) It took me several tries to get one right.
4. Design an entirely new rotary jig that moves that last ½” below the 4 ½” cylinder to up above it instead, i.e. shifts the axis down enough to clear the z-truck.* Of course the rotary software won’t work because it is calibrated on the current axis and is limited and to a max of 4 ¼”. So we need a new rotary jig that uses the regular Designer software OR a new rotary jig AND new rotary software!

I realize a couple of these suggestions are not only beyond the abilities of most of us users, but are beyond credibility itself. Since the CW is already an amazingly versatile machine – particularly as compared to others in its price range, I don’t feel this restriction is any great cross to bear. I feel confident I can justifiably reconcile to my family, friends, and indeed, the world, that my life’s accomplishments will not be diminished if I never carve a lithopane from 4” PVC tubing. I hope you all can find this peace too.



*OTOH, I have a new design in mind that just may be able to pull this off… no bets – more thinking and designing required. But I have other projects that need to be done first so don’t hold your breath.