marker pen driven over an 8x4 sheet help.

[JAZZCNC]

I meant not a problem with belts for a plotter, but if you've done a plotter and it's wasn't then fair enough. There was a plotter at school we dismantled that was belt driven without further reduction...and the rapid prototyper, laser cutter.

Yes on small printer type plotter this would probably be fine because of the small Diameter pulleys but on a machine this size the diameters get large so obviously the circumference does giving a very large pitch.!
Take for instance a 20T pulley which really for 8ft machine is about as small has you'd want to go then direct drive pitch is 97mm. . . . . It's bit like putting F1 engine in a dumper truck, it will carry what ever you want and go like fuck but the bastard won't stop or go round corners. :dance:

[Jonathan]

You could try the method where the board is supported with it's longest edge on the floor and a cable, up to 8+4=12' long supported at the top corners with a motor and pulley. The pen is suspended in between, so the cable makes a V-shape. By adjusting the length of the cable by spinning each of the motors you can get the pen to move to any position within the board. It's simple trigonometry to work out the relationship between pen position and motors. Then you enter those formula's into mach3 and it will run it as normal...
A standard belt driver plotter will probably be better, but since you're going to have to buy steppers and drivers for either you could try this initially as you only need a piece of string and a pen...

Edit: Wrote this post 2 days ago but forgot to press send!