Hi All,
My name is Bob Butcher, and I am working on a CNC conversion of my old J-head Bridgeport mill. I have about half the hardware done, and at this time I plan to use a Galil DMC 1850 control card to drive the three axis servo motors. I could program it using the Galil programming language, but that language is different from G-codes, so I probably will use Mach to interface with the control card.

I am a retired electrical engineer, and as most retired folks, have more time than money. I bought three NEMA 34 servo motors, rated for 600 oz-in, along with Gecko G-320 servo drives. I plan to use timing belts to reduce the motor speed 2:1 for more torque. I am going to build my own power supplies using old microwave oven transformers. I am designing and building all the hardware that I can, including even the timing pulleys. Building it is at least half the fun!

Bob
 

Bob,

    With 600 oz-in motors, I'd suggest you gear them down more than 2:1.  I have a Taiwanese BP clone I've just CNC'd with 850 oz-in motors, and 2.5:1 reducers, and it seems about right.  I think at 2:1 with smaller motors, you'll be very limited in rapids, and have problems with position loss on heavy cuts.  Also for the knee, if you go that route, you'll need a LOT more.  I'm going to 4.8:1 on the knee reducer.  At 2.5:1 I couldn't move it up at all.

Regards,
Ray L.

Thanks for the ideas. I am going to drive the quill instead of the knee, so that will help some. Since this is for hobby use, I am not too concerned about high speed moves, or heavy cuts, but of course I want it to work correctly. I will look at using a higher gear ratio.

Bob

Also consider too, with too little reduction, if you make a programming mistake, the motor can drive the table to places it best not be, very quickly. Make sure you install end of travel limits.
600 oz motors might be ok for ballscrews, but if you're using the stock lead screws, you'll use up considerable torque just turning them. I have built little belt reduction boxes and can get 5:1 just from that, and you can still do another 2:1 from the reduction to the screw.
Just a suggestion.
I love the Galil boards. They are so versitle and fun to program.
Good luck!