Ouch my eye!

The search for replacement stepper motors is on. The first step was identifying what is there already.

Two of the 3 steppers (X & Z) are easily identifiable, as I can read the labels on them. The 3rd stepper (Y) unfortunately has had the label completely darkened from the fire to the point where all I can tell is that is is a 0.9 degree/step stepper from the one side that is still readable.  Luckily with a peek at the laser at the Hacklab, and at a picture posted by a user (lasersafe@buildlog.net) of another ULS laser rebuild, I was able to identify the make, and possibly model for the unknown stepper. It is definitely the same manufacturer / series based on what is still discernible on the label of the motor. However it is quite possibly a different model than the one that is in both the Hackalab’s laser, and lasersafe’s UL25E. (the part number, while unreadable appears to be different)

So as a starting point we have:
X axis: Lin Engineering/41909V-51
[NEMA17, 0.9 degrees/step, 3.6V/1.2A]

Y axis: Oriental Motor/Vexta C6952-9012
[NEMA17, 0.9 degrees/step, dual shaft, 2.2V/2.2A]

Z axis: Pacific Scientific/P21NRXB-LNN-NS-00
[NEMA23, 1.8 degrees/step, 65V/2.3A]

The X axis stepper is the only one that is directly still available today. The Y axis stepper is not available under that part number, but likely has an equivalent under the current offerings. The Z axis will need to be sourced from a different manufacturer, as Pacific Scientific no longer exists. [they were bought out by another company, and the stepper division seems to be gone] Not that any of this is an issue, as I’m not wed to using the same motors, or even motors from the same manufacturers.

While we’re on the topic of the steppers, we might as well talk about the belts and gearing that are involved in translating the motors rotary motion into linear motion for each of the axis. Knowing this will be necessary for accurate positioning with the controller, and will aide in deciding on any changes in step resolution of the motors.

X & Y axis:
motor gear: 20 teeth/rev
timing belt: 12.5 teeth/inch
stepper motor: 0.9 degrees/step = 400 steps/rev

12.5 / 20 = 0.625 revs/inch
400 * 0.625 = 250 steps/inch

4 mil per step isn’t too bad, but further resolution can easily be obtained via microstepping, at the expense of torque in the motor. 4x is probably fairly safe here, giving 1 mil resolution. 8x or greater may be possible, but will need to be verified by determining the forces at play in the mechanics. It will be interesting to see how far the official ULS electronics push it.

Z axis:
motor gear: 20 teeth/rev
shaft gear: 30 teeth/rev
acme shaft: 10 thread/inch = 10 revs/inch
stepper motor: 1.8 degrees/step = 200 steps/rev

10 * 30 = 300 teeth/inch [@ lift-shaft]
300  / 20  = 15 revs/inch [@ motor]
200 * 15  = 3000 steps/inch

Plenty of resolution here without needing to resort to microstepping, and we don’t need a high level of accuracy here on the Z axis anyway. The step-down gear ratio here is likely just for mechanical advantage to lift the engraving table, and not for added resolution.