First I must give an apology because this is such a long entry. But if you can wade through it you will see that I am at wits end in resolving the problem because I’ve already tried everything reasonable.

I am a bit OCD but it helps with such a complex machine. I have a C machine and I am using the LHR rotary jig – the fancy metal one. I have a Ringneck Blues DC plus I keep the machine scrupulously clean by vacuuming out any and all remaining chips after any carve. I frequently vacuum chips out of the machine with a crevice tool while it is operating to prevent build-up on the belts. I also regularly clean and lubricate the entire machine including the rails IAW the seminars during the CW Conferences of 2012 and 2014 (same talk both years). In short, I take very good care of my machine and except for melting a flex cable by using the wrong lubricant, I have been relatively problem free. (hint: READ THE MANUAL)

I have been making a lithopane pattern of four fairies Click image for larger version.  Name: FourFariesCompositeOPT.jpg  Views: 57  Size: 550.5 KB  ID: 78217(FourFariesOPT.jpg) that carves the full circumference of 3” PVC. I have carved numerous copies of this pattern now and I have only once been successful in achieving a near exact 360° of carving. Usually the carving finishes before the machine has moved the PVC a full rotation leaving a thin ridge of uncarved surface that is 1/8” - ¼” in width. Click image for larger version.  Name: NoCarveRidge.jpg  Views: 59  Size: 2.00 MB  ID: 78213(NoCarve.jpg) I have to carve it away with a Dremel tool which I have to admit is not near as precise and the CW and it shows with trans-illumination.

I have tried several methods to correct the problem. First I just extended the pattern over the edge of the flat projection in Designer. This shows up in the Designer rotary projection window as a perfect carve Click image for larger version.  Name: FourFaries-std.JPG  Views: 49  Size: 228.8 KB  ID: 78214(FourFaries-std.jpg). It does not carve that way. Any part of the pattern that overhangs the flat projection board size doesn’t get carved. It’s like it doesn’t exist. Then I increased the “board size” of the project tube by increasing its diameter. Click image for larger version.  Name: FourFaries-wide.JPG  Views: 39  Size: 207.3 KB  ID: 78215This gives me a little more “board length” to make the machine think the pattern is lengthened. When you load the part you manually tell the machine the part diameter is 3.563” rather than letting it calibrate (which would result in the actual of diameter of 3.5”). This trick resulted in the ONLY successful carve of a full 360°. Unfortunately the next one was worse than ever – over ¼” ridge. So even tricking the machine will not give a consistent result.

I ascertained the problem to be slippage of the project somewhere between the machine traction belts and the carved piece. I first thought the carved piece was slipping in the end plug but then I put a small screw to prevent that Click image for larger version.  Name: PlugScrew.jpg  Views: 35  Size: 1.95 MB  ID: 78216(PlugScrew.jpg) and there is absolutely no movement around the plug. Since the plug is held in the jig with two screws already, there is no way it could rotate independently of the jig either. So the slippage must be located at the interface between the rubber “fan belt” on the jig and the rubber traction belts of the CW machine itself. I thought putting a bit more head pressure would solve the problem but with a little down shove on the upper chassis (another trick I learned at the CW Conference) I can get over 140 pounds of head pressure – actual measurement! Since the manual says normal head pressure should be 75 to 85 pounds, I don’t think more head pressure will solve things.

So that’s my problem. Short of putting some sort of sticky goo on the traction belts (and ruining them for anything else), does anyone have an idea on how to achieve an accurate 360° carve in PVC?

Edit #1: I carve this project in "Optimum" setting so it will make very small cuts to minimize the pressure the tool will have on rotation. It takes over 3 hours to carve.

Also: My profuse thanks and Muchos Kudos to Michael Tyler who first successfully carved PVC tubing and showed it at the 2014 CW Conference. I had the idea before I saw how he did it, but he saved me making numerous mistakes because he made them first! (like trying to do it with 4" PVC) I still have more ideas but he did all the groundwork. If you've never met him, he's a real nice guy too. Thanks Mike.