I looked at the videos on Donek tools site again, the knife is still in contact when the machive changes direction, just with a very much reduced DOC, the castor on the blade still has to have some resisitance to operate. Has to be a pain to code!

An eBay search for "Roland Blade Holder" turns up plenty of vinyl cutter holders, not sure if these have the bearings in them, or if the bearings are in the part of the machine that holds them, for the money (£7ish upwards) though, they'd be worth a look at least as a basis for thin material.

Still trying to find the links I had for other drag knifes, I must learn to be more organised!