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Hi Bill,
What you want to do is perfectly feasible - but may involve a bit of "development" to get where you want to go!
First, unipolar vs bipolar - this is just about whether the coils are wired to carry current in one direction or both directions - if both directions, they'll be wired separately, unipolar can have a common "ground".
You'll need to measure the torque needed so you can choose a motor - putting a heavy facing cut on with a torque wrench on the crossfeed would do it, then factor in torque multiplication from the reduction between motor and crossfeed (see below) and double / treble it
To get the control you want, you could just mount the stepper directly to the cross-slide screw, but at the expense of only having 200 steps / turn - better would be to have some reduction between motor and screw, even better would be reduction plus "microstepping" (a controller feature) - this only works with bipolar motors, as the coils need to be individually wired, but by varying the currents in the 2 coils it's possible to make part-steps, e.g. 4 or 8 (sometimes 16) micro-steps for each of the standard 200 steps/rev. - it's worth making the individual steps / microsteps a sensible increment, e.g. 1/10 or 1/25 of a thou", perhaps with toothed belt and suitable sprockets.
If you go for a ready-built controller all it needs (apart from a power supply, which can be as simple as a redundant PC supply or parts from a dead hifi amp) is a source of step and direction input pulses - the step pulses can be generated by a 1-chip timer circuit (google "555 timer astable"), direction from a suitable switch! Using a controller with standard step/direction inputs opens up the possibility of CNC at a later date, too - CNC software's free and can run on a relatively low-spec PC...
The CNCzone site has lots of info on steppers, controllers, breakout (PC) boards, software etc. (including home-brew versions), probably worth a look / signing up (free).
Dave H. (the other one)
What you want to do is perfectly feasible - but may involve a bit of "development" to get where you want to go!
First, unipolar vs bipolar - this is just about whether the coils are wired to carry current in one direction or both directions - if both directions, they'll be wired separately, unipolar can have a common "ground".
You'll need to measure the torque needed so you can choose a motor - putting a heavy facing cut on with a torque wrench on the crossfeed would do it, then factor in torque multiplication from the reduction between motor and crossfeed (see below) and double / treble it
To get the control you want, you could just mount the stepper directly to the cross-slide screw, but at the expense of only having 200 steps / turn - better would be to have some reduction between motor and screw, even better would be reduction plus "microstepping" (a controller feature) - this only works with bipolar motors, as the coils need to be individually wired, but by varying the currents in the 2 coils it's possible to make part-steps, e.g. 4 or 8 (sometimes 16) micro-steps for each of the standard 200 steps/rev. - it's worth making the individual steps / microsteps a sensible increment, e.g. 1/10 or 1/25 of a thou", perhaps with toothed belt and suitable sprockets.
If you go for a ready-built controller all it needs (apart from a power supply, which can be as simple as a redundant PC supply or parts from a dead hifi amp) is a source of step and direction input pulses - the step pulses can be generated by a 1-chip timer circuit (google "555 timer astable"), direction from a suitable switch! Using a controller with standard step/direction inputs opens up the possibility of CNC at a later date, too - CNC software's free and can run on a relatively low-spec PC...
The CNCzone site has lots of info on steppers, controllers, breakout (PC) boards, software etc. (including home-brew versions), probably worth a look / signing up (free).
Dave H. (the other one)
