[vbgraves]

Hi, I've refurbished a Mini-Tech benchtop mill and now have it working, but I've noticed it "jumping" in the X and Y directions during some cutting operations, and the effects can be seen in some of the parts I've made. At first I thought it might be the Delrin lead screw nuts, so I replaced those, but while I had it disassembled for installing the new nuts I noticed the motor coupling could move axially within the motor itself, irregardless of whether the motor was energized or not. I couldn't easily put an indicator on it, but it is certainly visible to the eye, and I'd guess it's on the order of 0.050.

The motors are Slo-syn as shown in the attached image. Can anyone offer suggestions as to a fix? Assuming motor replacement is required, anyone have suggestions for comparable motors? These are 4-wire, bipolar motors, and I have a Xylotex board that is limited to 2.5 A/phase. Thanks.

[ger21]

The fix is don't rely on the motor for the axial location of the screw. The screw should be rigidly mounted with bearings to handle the axial loads.
Steppers are not designed to handle axial loads.

[vbgraves]

Thanks for the input, and I hear what you're saying, but the system was not originally designed with bearings. The lead screws connect directly to the motor couplings and are supported on the opposite end by the delrin nuts. Not sure I can easily implement a set of bearings, but if you have suggestions, I'm open to options.

[H500]

The motor bearings are spring loaded. They are not designed to take an axial load. The only proper fix is to add bearings. With your design, a pair of bearings can easily be added if the motor end.

[RomanLini]

Many of the new hybrid motors have a strong fixed axial bearing (the front bearing). Replacing the motors with modern motors designed for axial loads should fix your problem.

That old slo-syn motor was not rated for axial loads, some of those even have axially-sprung bearings using a wave washer.

[vbgraves]

Thanks for the info on the motors. It certainly feels like they are spring loaded. I'll look into replacing them.

[vbgraves]

So I've looked at the motors on the Automation Technologies site and thought the 156 oz-in motors (High-Torque Stepper Motor, Stepper Motor, Driver, Stepper Motor kit, DC Servo Motor, DC Servo Motor kit, Stepper Motor Power Supply, CNC Router, Spindle, and other Components. Automation Technology Inc) that I thought would be a close match to the existing ones in terms of performance. My concern is that that are rated for 3A/phase, whereas the Xylotex board I have can only supply 2.5A/phase.

Automation Technologies suggested I consider some stronger motors (High-Torque Stepper Motor, Stepper Motor, Driver, Stepper Motor kit, DC Servo Motor, DC Servo Motor kit, Stepper Motor Power Supply, CNC Router, Spindle, and other Components. Automation Technology Inc) that are rated for 2.8A/phase.

Any comments on whether this would be a good replacement? These are a little pricier than I would like, so if you know of others that might also be suitable, I'd be interested in suggestions.

[H500]

What lead you to believe that those are designed to take an axial load? I have motors from Keling and all are spring loaded. I have never personally seen one that wasn't.

[vbgraves]

So what I did in an attempt to remedy the situation is to provide some axial preload by placing spring washers between the X and Y motors and their lead screw couplings. Simple and cheap. Ran the system today, and it performed much better, but I may have to adjust the preload a little before I declare success.