DivisionMaster Motor Size
We keep getting asked what motor do I need and this is an attempt to outline the various options. Anything up to 6" that is running smoothly whill be handled quite happily by the 180Ncm motor, but over 6" you may want the option to add extra power later. See new notes below.
The DivisionMaster itself will only provide 2Amps at 24V which is fine for the Nema23 motors and while it will drive the bigger ones, there is little difference in the power created. The 350Ncm motor has only recently become available, and is a good option for driving direct from DivisionMaster while allowing the option later to add an external stepper driver which will give 4Amps at 48V ... i.e. around 4 times the power ... if your setup needs speeding up. The 650Ncm motor then adds a little more power but requires a bigger stepper driver capable of handling 72 or so volts and this is what is implemented in the external driver pack.
In practice, given the worm drive in a rotary table, the Nema23 180Ncm motor WILL drive a 8" table quite happily provide that the table has been cleaned and any tight spots addressed. A little grinding paste can make a table run smoothly if there is the odd tight spot. My own 6" table had a 0.25deg tight spot where it would stick when adjusted with very low backlash everywhere else and once addressed, the table now runs cleanly! ( Just clean out the grinding paste after use ;) ).
If you are only indexing using the stepper motor, then the Nema23 will be fine, and even if crossing out, one just slows down the step rate. Problems can arise if you add a heavy chuck or other heavy load to the rotary table so it is a question of what you are planning to do with the table. A 10" or 12" table can be turned quite happily by the DivisionMaster direct, but add a 10kg chuck and things will grind to a halt. At this point, in the past one would have moved to NEMA34 motors, but the NEMA23 motor development has now added 3Nm and 4Nm power in the same small package as the 180Ncm. Well almost, as the motor is a little bulkier, but still fits the same mounting arnagement. While the standard DivisionMaster will drive the bigger motors, the lower voltage and current restrict the power available to that of the smaller motor, which is why the DMSuper option has been added. This provides a 45V 160W power supply and matching stepper driver.
The older NEMA34 350Nm motor is now somewhat obsolite and I would suggest that the 680Ncm is of little practical use since it needs at least a 70V supply with one of the much bigger stepper drivers capable of handling that voltage.
The 4" to 6" tables on the whole have the same mounting arrangement for the handle, and 99% of the time will have a 12mm shaft which fits well with the 25mm oldham couplings. So we just need to confirm the shaft size. Many of the 8" tables seem to have the same 12mm shaft, but 14 and 16mm shaft sizes are not uncommon. At this point we are moving outside the range that the 25mm coupling will support, and the larger size couplings will not go DOWN to the 6mm shaft size of the Nema23 motors, so a custom sleeve of some sort tends to be the best option. This adds another advantage of the Nema34 motors with the 350Ncm using a 10mm shaft, but the newer motors have 8mm shafts which helps matching.
Rotary Table Motor Coupling provides details on the various oldham coupling options.
CNC Component Shop has a few options for supply of motors and parts to assemble your own. Only problem that needs to be watched out for is that while the smaller motors tend to just have a bundle of cables coming out of the side, the newer motors have a housing giving better strain relief and resulting in the need for a different mounting box machining.