You have a great start here but I think there is some room for improvement. Note that I am not writing from practical build experience but from having followed dozens of build threads and absorbing comments from people who know more about this than I ever will. So take what I say with a grain of thought but please understand that I hope my comments will help shorten your path to success.
I think you need to bring up the stepper voltage considerably. Performance at 24 volts will be poor. Anyone who, like me, bought a Taig mill with an Allegro based controller running high inductance steppers should be able to attest to that. According to Gecko Drives stepper voltage should be 32 * sqrt(inductance) for best performance. Thus the first motor you listed wants about 43 volts and the second one about 83 volts (in parallel, series is much higher). I don't know what drives you are planning to use but the first motor draws a fair chunk of current so something like the Gecko G540 would be out of the question. On microstepping: its main purpose is to smooth out the motor at low speeds. It isn't the greatest way to increase resolution since the distance between microsteps isn't always even. There is a point of diminishing returns with microstepping. That is around 10 microsteps according to Gecko Drives. See: https://www.geckodrive.com/gecko/images/cms_files/Step Motor Basics Guide.pdf
As for the relationship between the motor, support block and screw, one of the roles of the support block is to isolate the motor from the violence of the screw. Support blocks have robust preloaded angular contact bearings while motors have comparatively wimpy deep groove bearings. With the mounting arrangement you are proposing, the motor will be subjected to all kinds of stress as the screw expands as it gets warm or if it starts to whip. In any case for short screws like you will here, you don't need to support both ends providing the screws are a sufficient diameter. The 16mm screws you are specifying are more than adequate. Look for the Critical Speed calculator on this page: http://www.nookindustries.com/EngineeringTool/Index to figure out what will work. It is interesting to note in their fixity examples, none has the motor opposite a bearing block.
I don't know where Mach 4 is at but Mach 3 has well documented issues with threading and dealing with index pulses (it can only deal with 1 per rev so it doesn't track very well). You might want to consider Linux CNC. It is more work to get going but is more robust than Mach 3.
If you have access to FEA software, run an analysis of your design. I think you will find that very little of the material above the spindle/bed plane contributes to rigidity. Take that part of your weight budget and put it where it will do more good and build up the enclosure. For instance, extra mass around the spindle and the spindle/bed interface is rarely wasted.
Have you see this build? It is similar to yours: http://www.cnczone.com/forums/vertical-mill-lathe-project-log/281738-cnc-cad.html
bob
I think you need to bring up the stepper voltage considerably. Performance at 24 volts will be poor. Anyone who, like me, bought a Taig mill with an Allegro based controller running high inductance steppers should be able to attest to that. According to Gecko Drives stepper voltage should be 32 * sqrt(inductance) for best performance. Thus the first motor you listed wants about 43 volts and the second one about 83 volts (in parallel, series is much higher). I don't know what drives you are planning to use but the first motor draws a fair chunk of current so something like the Gecko G540 would be out of the question. On microstepping: its main purpose is to smooth out the motor at low speeds. It isn't the greatest way to increase resolution since the distance between microsteps isn't always even. There is a point of diminishing returns with microstepping. That is around 10 microsteps according to Gecko Drives. See: https://www.geckodrive.com/gecko/images/cms_files/Step Motor Basics Guide.pdf
As for the relationship between the motor, support block and screw, one of the roles of the support block is to isolate the motor from the violence of the screw. Support blocks have robust preloaded angular contact bearings while motors have comparatively wimpy deep groove bearings. With the mounting arrangement you are proposing, the motor will be subjected to all kinds of stress as the screw expands as it gets warm or if it starts to whip. In any case for short screws like you will here, you don't need to support both ends providing the screws are a sufficient diameter. The 16mm screws you are specifying are more than adequate. Look for the Critical Speed calculator on this page: http://www.nookindustries.com/EngineeringTool/Index to figure out what will work. It is interesting to note in their fixity examples, none has the motor opposite a bearing block.
I don't know where Mach 4 is at but Mach 3 has well documented issues with threading and dealing with index pulses (it can only deal with 1 per rev so it doesn't track very well). You might want to consider Linux CNC. It is more work to get going but is more robust than Mach 3.
If you have access to FEA software, run an analysis of your design. I think you will find that very little of the material above the spindle/bed plane contributes to rigidity. Take that part of your weight budget and put it where it will do more good and build up the enclosure. For instance, extra mass around the spindle and the spindle/bed interface is rarely wasted.
Have you see this build? It is similar to yours: http://www.cnczone.com/forums/vertical-mill-lathe-project-log/281738-cnc-cad.html
bob
