Cats cradle anyone?

[John Hill]

I have just about finished my pantograph router and I am thinking how nice it would be to add CNC so the requirement is to move the trace point in X and Y directions.

Rather than use screws or whatever for such lightweight work I am wondering if a cat's cradle would be practical. The principle is simple, for the 'Y' direction a single wire (stainless steel fishing trace for example) is routed around four corner rollers and doubles back on itself so that there are wires on each side of the rectangle moving in the same direction and a cross piece is anchored to these wires so as to move in a parallel fashion over the base. A simple loop of wire and a single stepper to be fixed to the cross piece to give the 'X' direction.

My plan is for a 30x30 inch X,Y, rectangle which, as my pantograph scales 1:2.54, gives me a 30cm square work space for the router.

Anyone use wires for linear motion?

Thanks.

[vladdy]

those were commonly used on plotters for the longest time, and worked well, however I'm not sure how much 'stretch' you might get. After all, a plotter only has friction load from the pen working against it. If you run larger cables, then you need larger pulleys for the 'minimum radius' of the cable, and also a larger pulley on the stepper motor which makes it work harder as well...

you could probably try a mockup, and see how much static lateral load you can obtain before your 'stretch' exceeds your limits..

mind you, the new generation of firewire and other fishing lines is pretty small diameter for their rating

.enjoy..

[BobWarfield]

I think this thread is all about your cat's cradle:

http://www.cnczone.com/forums/showthread.php?t=51485

Cheers,

BW