Just thinking stuff up in my head, it might be all garbage, but bear with me.

I understand that positional accuracy is determined by the pitch of your lead screw and the no. of steps per turn of your motor, but what about speed? Is this purely controlled by the amount of voltage applied, or are the steps timed? Now the reason I ask is I'm wondering how slow and accurately you can turn two motors and keep them in step. What I'm envisioning is a (relatively) slow moving turntable holding a work piece as a 4th axis and the Z axis moving up and down with a tool to machine on the edge of a disc. The rotation of the 4th axis and the travel of the Z axis would have to be kept in sync, within a given tolerance. Is this possible/practical/feasible? And would it all be controllable through EMC2?

The speed of a stepper motor is controlled by the pulse timing. Give it one pulse and it will move to its new position and hold it indefinitely. A servo, I’d guess, would do the same.

In a servo system positional feedback is constantly provided and voltage is applied proportionally to the amount of error- meaning that motors are constantly trying to find the right position regardless of performance variances. Now- there are other issues at play too (servos linked in an axis need to be "geared" together, and encoder data needs to be master/slaved), but using servo or stepper, high accuracies can be achieved.

Thanks guys! So the speed is all in the timing then, and so would be controlled by the software, such as EMC2, right? And what I suggest can be achieved with a suitable setup of stepper or servo? But when you say "geared" together, do you mean physically geared, or in some kind of closed loop electronic control? I'm assuming the latter, and again controlled by EMC2.

Now, what kind of torque can these motors provide. If my motor was connected directly to the turntable, and my work piece had a 6" radius, the load on the motor would be the force of the cutting tool @ 6". And now I'm lost because I wouldn't know where to start figuring that out! Clearly depth of cut, size of tool, material, feed rate would all need to be considered! But does it at least sound doable? I don't need a definitive soultion, I just want to make sure I'm not heading down a dead end.

I've really got to stop reading this forum late at night, it hurts my head.

I should really just order my micRo and start playing about with it all, but unfortunately I just spent most of my budget at a tool sale. :sigh:

Have to be brief, but everything you want to do is easy to do. When Robin said 'geared' he was referring to the expression used for linking the amps in software, not mechanical gearing.

I was pretty sure that's what he meant. I'm pretty familiar with CNC as an operator, but less so when it comes down to building it at a component level. I'm reasonably confident in what can be achieved, but it's always nice to ask and have a confirmation!

Yep, it's electronic gearing. The problem being that if the two motors are rigidly linked (via the Y axis), then variance in the motors could cause them to fight when they seek their correct position. This is dealt with either in software (EMC) or in hardware (expensive industrial drivers and controllers).....

As far as the torque of the servo motors is concerned, they have enough for one motor to drive the Y axis with me sitting on it. I've been meaning to start exercising again.... But anywho it has torque to spare. Or let me re-phrase, it has enough torque to push any reasonably priced spindle or router I can think of.

Diet or not; you're still the first CNC human!

Whoa! I had a thought (rare occurrence) and found the answer to the already-asked question (another rare occurrence).

I was perusing info on Gecko drivers and wondered how the two motors driving one axis were synched.

So, each of the two motors driving one of the axes is controlled independently but one is master and one is slave. The software handles all the annoying details of keeping them where they belong. Is that correct if overly-simplified?