I am well on my way to building a small desktop cnc, predominantly for pcb milling. My interface is done, as is much of my machine, but I am currently waiting on nuts for my leadscrews and a few other bits and pieces.
I have 3 of these:-
Vexta PK243-03AA Unipolar Stepper motors
Yes, unipolar have their dis-advantages, but the main advantage was that they seem to work well with my interface (uln2803 board based on Etch CNC), which was CHEAP to make. I am now wondering if they are likely to be underpowered.
My design is a simple moving bed (ie. X-Axis bed moves, Y-Axis and Z-Axis move overhead). My linear rails consisting of Aluminium Equal angle and skate bearings are very free moving, and fairly light (12mm mdf bed weighs not more than 500grams, total Y & Z Axis arrangement including dremel shaft is less than 1.1Kg).
Leadscrews are 1/4 inch (6mm) 20tpi teflon coated, approx 12inch (30cm) long, are fairly light. Nuts coming are of good quality and should be relatively friction free.
Looking at my motors, I think I may have made an egregious error in the size of motor I have chosen, as they only have 22oz-in / 0.16N*m holding torque.
Have I bit off far more than I can chew with using such small motors?
I will be going ahead and mouting everything and testing anyway, but if anyone has any opinions I would appreciate them. Specifically, if you have experience using small motors, or those with a similar holding torque I would be most interested.
I am not a maths guru, and have judged it by eye as to whether the motors will actually be strong enough. Even though I have my doubts, I still think I'll get a useable machine (just won't be breaking any speed records)
Anyway, to those who chime in with their $0.02, thanks in advance.