I went up to see a 6'x12' Shopbot table last weekend. It was a neat setup, and the first full-size CNC router I've gotten a chance to look at. This one was setup on the factory stand, which was a nicely painted (blue) steel stand that looked plenty ridged.
This particular machine had not been fine tuned. The router was not perfectly vertical so one side of the bit dragged more than the other side (not a problem in though cuts) and some of the rollers were not adjusted well. However it seamed to do a nice job on the wood products that they were making.
The design where the gantry rides on "precision ground" angle iron was interesting. The rack and pinion drive was also interesting. It used dual servos on the X axis, and single servos on the Y/Z axis. The Z axis had a coiled spring to counter-balance the weight of the router, so it did not crash when the power was removed.
It looked like a reasonable setup, but I am unsure what kind of tolerance that it can keep. The web site claims 0.015", which is probably achievable with a well tuned machine. The one I was looking at was probably more like 0.025" or more.
I don't think it would do a good job on metals at all (which is not surprising, it is not designed for metal work.) The only thing that keeps the router from lifting is a couple of springs holding the X axis servos to the track, and the dead weight of the gantry. The Z axis also had room for it to lift, as it is not rigidly mounted to the rails, but lets gravity hold it down (with some safety rollers to keep it from being thrown off the track).
So I would not try to do fast precision pocketing in metal, but with good adjustment, I see no reason it can't do about anything in wood.
I also found it interesting that there were no mechanical stops on the Y or Z axis to prevent the machine from running off the ends of the table. I would like to see a bolt or two that stalled the head incase of a bad program (or a bunch of missed steps), rather than having the gantry roll off the end and crash.
The metal plate that is used to set the thickness of the material was neat. Is that a feature easily available for a home-built machine?
Zeph  |