Since polycarbonate is "soft", I tend to run a single pass on any piece up to .25". Spindle speed @ 24K, cut speed @ 200-400 IPM.
As everyone else mentioned, though, thinner strokes will lift. They just will, since there's less material holding the cut piece down.
Other factors that have an impact:
- Nesting. How close together or far apart the cut parts are
- The condition of your spoil board. If yours has a surface resembling a topographical map, you're going to be hard pressed to get it to hold its vacuum on most any cut.
- Is the vacuum actually the right one for the size table you have? It may not have the "power" to hold parts across the working area. Reputable manufacturers will make sure you get a vacuum that "pairs" appropriately with the table you're running, but if the table didn't come with one and you bought it yourself, you may not have gotten the right one (there's an actual mathematical formula for figuring what's needed). I've also seen a situation where a very good used table came with a vacuum that was better suited to a table maybe half it's size- because the company that sold it to the broker who reconditioned it kept their original pump for the new table they'd purchased. The broker (not paying attention or just not caring) paired the table with a pump they had on hand and the guy who bought it didn't know any better.
- Do you block off the rest of the table, so that the vacuum is "focused" on your cutting area? If you don't, you should.
- Your bit. Though I don't usually use them (or keep them on hand, even), a down cut bit can help eliminate lifting.