2D only version of the Skycam?

Shop Forum Makelangelo Polargraph Art Robot 2D only version of the Skycam?

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    I have an old pattern torch I want to convert to CNC. Basically what it is, is a SCARA type arm with no motors at the joints. It holds a cutting torch at the end of the arm. To move around it has a 0.25″ diameter magnetic, knurled shaft directly above the torch. A motor rolls the magnet around the edge of a steel pattern.

    The patterns have to be cut 1/8″ undersize and for every different piece to be cut, a pattern has to be made. That’s the time consuming, often annoying part of using the old beast.

    How I want to add CNC is attach a frame with a stepper motor at each corner with a cable. To attach the cables to the arm will be simple. Make rings that fit over the magnetic shaft.

    They won’t have to be very strong motors. I can push the torch around with the tip of a little finger.

    The tricky bit is the software. I want to run it with LinuxCNC, which reads G-code files. Converting from G-code to the commands required to operate a drive system like this? I have no idea how to do that.

    All four cables will need to stay in tension all the time. Since it will only move in a 2D plane, there’s no need to bother with calculating cable lengths for vertical movement.

    A CNC retrofit like this could bring many old pattern torches out of the dark corners of shops.

    Gas torches are typically used on 1/4″ thick and thicker steel so they don’t need features like automatic torch height control and many of these don’t have automatic torch on and off. Plasma cutters can also be mounted on pattern torches and would benefit from automatic height control and bigger motors for high speed traverse between cuts.

    The big picture goal is to take a tool that already works and make it more versatile, without the expense of building an X-Y gantry. Hackerspaces would love it, pick up an old pattern torch for a cheap scrap price, add cheap CNC and have a heavy duty machine for about the same as people build light duty little gantries.


    I’m not sure I follow. Have you looked at http://www.corexy.com/ ?


    That looks like it could work and instead of a square frame it could be U shaped. More complex mechanically than four straight cables and four motors but could be treated the same as a regular X-Y mechanism.

    It’s like the H-Bot drive with the added crossover keeping the gantry bar straight.

    Still would be cool to add the cable robot drive function to LinuxCNC, which should be able to provide for fast motion and moving the connection point of the cables with the usual XYZ coordinate inputs used for machine tools.


    I… I don’t really understand what you’re saying. Maybe if you had some pictures or something?


    It’s a torch similar to this one. http://www.hellotrade.com/esab-usa/ultra-graph-single-torch-pattern-cutter.html

    Here’s an image of the concept. http://www.partsbyemc.com/pub/pattern-torch.jpg Replace .jpg with .psd for a version with pieces you can move around.

    Sooo, all four cables in constant tension and the motors commanded to move in and out as needed to move the end of the arm. Except for arcs that happen to center on one motor, all four motors would have to rotate in different directions and speeds for any movement.

    Then there’s the issue of translating from G-code to this…

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