I too had problems with the object slipping on the rollers...In my case I was engraving some glass beer mugs that had a heavy handle on one side.All went well for the first few but after a while they started to slip. I didn't notice until one was obviously not right...I tried masking tape around the top edge of the glass that rests on the driven wheels...that worked ok. Then I tried slipping a couple of wide rubber/elastic bands around the top..I still use this method as it is a good "grippy" surface.
One query I have about the epilog rotary thing is...are there smaller idler wheels available or has any one tried making some?.The reason is, I've tried engraving a beer mug with a large heavy base that is a lot larger diameter than the top..the adjustment on the carrier doesn't allow the glass to be lowered enough to get the surface horizontal. When I tried moving the wheels to a "thinner area of the mug...the handle fouled the wheels..
thanks...Dave