Talked to Graphic Marking Systems.... didn't get anywhere.
Talked to local Graphtec dealer AND the local rep. Both of them talked me out of the flatbed...?????? Said it would still cause blade drag?
Tried a Summa.... had blade drag. But it was NOT their tangential machine, and I heard they have a sandblast style blade holder for it, to allow more lift? True?
Any dealers on here... come on guys... my moneys green!!!!!!
That's a shame because GMS is probably your best shot at finding a solution. They do what you want to do in a daily basis. Your Graphtec dealer sounds like he's never attempted what you want to do.
Tangential tool head movement has little or nothing to do with dealing with what we are calling blade drag which is the resistance to cutting the material being converted to a force which is attempting to move the material out of the way. The only reliable response to keep the material from shifting is to either hold the material down as a flatbed does or to grip the edges with a solid, non-slip mechanism such as the tractor feed mechanism found on Gerber plotters.
I guarantee you that I can cut your 18 mil stock at full or near full speed on my Gerber Envision 375 plotter ... providing you use a 15" punched material at the base material before lamination. And the Envision is not tangential, it uses a swivel knife.
Try this: Take the easiest material you have to cut and cut a 1/4" stripe that is 10' long. When it's done, measure the 1/4" at both ends and you will likely find an error in the width at the start end which is caused by material movement due to blade drag on the first cut. Now cut half a dozen such stripes one above the other and measure your compound errors that are generated by blade drag.
If you are not aware, I invented a friction feed adapter for Gerber plotters back in 1988. We sold over 1,000 units. I understand the physics involved.