Hi,

I have an old Unisys XY pen plotter which I'd like to convert into a vinyl cutter. I got a blade holder and blades on ebay, and it looks like everything fits great.

The problem I'm running into is that the blade just doesn't press into the vinyl with enough pressure to cut. It pretty much just scratches the vinyl. So, my question for others that have done similar conversions... do you have any tips for increasing the blade pressure, or making it adjustable? It looks like there's just a solenoid that pulls one side of a lever to push the pen down, plus a couple springs. I'm afraid that if I simply replace the downward pressing spring with a stiffer one, the blade won't retract. I'd probably run into the same problem by just adding weight to the "pen" side.

One thought I have is to add a servo that both pushes and pulls, that way I don't rely on springs and a weak solenoid to set the pressure. But that'd probably be pretty slow. I could also upgrade the solenoid (I haven't checked the specs of the current one yet). Or maybe setting the downward pressure with a spring and flipping the solenoid to lift the pen would be better? I could possibly over drive the voltage to the solenoid as well (I haven't looked into any of the circuitry yet).

I'm also slightly worried about overloading the carriage, so I'd like to keep the head as small and lightweight as possible. I don't want to stall the stepper motors by trying to move heavy parts (plus the extra drag of the blade in the vinyl).

Anyway, if anyone has any ideas, I'd really appreciate the input. I have a 3D printer, so I can easily fabricate plastic parts, if that helps (I think I may need to make a more robust "pen" holder).

Oh, and this is just a hobby thing... I'm sure there are better machines to do vinyl cutting, but I've had this plotter for 10+ years, and have been looking to repurpose it... and this seems like the perfect job for it. I don't have enough need to justify buying a commercial vinyl cutter.

Thanks,
Pat