Hello,

I am struggling with a stutter problem that seems to come and go. I posted in the electronics section assuming the issue is the power supply. Before I go and replace the PS I wanted to throw this past the DIY forum and see if anything else comes up.

The problem: The machine will randomly stop while cutting occasionally it will studder a bit prior to stopping. This has happed in the x and y axis.

Solution Identified from Electronics section post: Switching power supply going into foldback/protection mode due to quick current pull from steppers. Un-regulated power supply is better suited to the stepper motor application.


Details on the machine:
- Frame is 8020 constructions with aluminum tooling plate uprights
- Rough travel: 48" x 24" x 7"
- Nema 23 motors (425 oz-in holding torque, 3 A rated current, 6.5 mh inductance)
- DM-556D stepper drivers
- Dual motor Y axis
- 5 mm pitch ballscrews (not ideal but was readily available when I built it)
- Limit switches, e-stops, & motor wire all runs in shielded twisted pair that is grounded to a common point in the control box (using mechanical limits and only use them for homing as there have been false triggers from vibration)
- Motor acceleration is set pretty slow at 6 in/s^2
- Typical cutting speed 60 - 100 ipm (Limited by my confidence in the machine to run without stalling somewhat limited by 5mm pitch ballscrews)
- Tooling: Carbide roughing 3 flute 3/8" or 1/2"
- Spindle: 2.2kw water cooled
- Controlled from Mach 3 through a UC100 into a C10 Breakoutboard

Initially there was only one switching power supply (non-branded 48V 12A) that fed the 4 motors. It was fine for a while but over time has started to show the stuttering issue more frequently.

Second power supply was added (Meanwell 48V 12A), this seemed to help but did not fully resolve the issue on heavier cuts.

The non-branded powersupply was replaced with another Meanwell of the same specs. Each of the power supplies are wired to a single point 120v connection. The same goes for each stepper driver.

With the two meanwell switching power supplies the machine is still showing the stuttering behavior somewhat randomly. I started up the machine today to run some plywood and two times in a row had the machine stall on me while jogging between the holes it was cutting at a constant speed. This stall was a few minutes after I started the machine up.

Below is a link to a video that show the machine stalling while cutting out a skateboard blank. This cut, using a 1/2" 3 flute carbide rougher, will pull 3.8-4A on the spindle readout. Based on the spindle I believe this to be about 50% load.

Theory on what is happening:

The stepper motors pulling enough additional current, in a fast manner, when the machine goes into a heavier cut causing the protection circuitry to think that there is a short circuit causing the power supply to foldback voltage or current or both causing the stall.

When there was only one power supply driving all 4 motors they would all stop once this stall occurred. Now that there are 2 power supplies (1 has both Y motors, the other has X and Z) X will keep going when the Y stall occurs.

Today I tried to prove what was happening by connecting the multimeter to the outputs of the Y axis power supply and watch the voltage. Naturally the machine did not show any issues while the multimeter was connected. I plan to continue to do this to see if I can catch something happening during a stall event.

I have done the math on the 5mm pitch ball screw at 50 RPM increments up to 200 ipm following the torque curve of the motor. I have a hard time believing the motor is stalling on the axis that has two motors vs one (There are heavy cuts in both directions the video just happened to capture Y which is the failure the is most frequently seen). At 100 ipm I think I should be able to stall the spindle prior to stalling the motors.

I have run the machine off of a different computer to prove that windows isnt doing something fishy in the background stealing resources from Mach.

Am I just running into the limits of a protected switching power supply?

https://photos.app.goo.gl/3d1hPXAWR7jp3ERT9

At some point I would like to update the X and Y ballscrews to 10mm pitch as once I can get this stutter problem resolved I will want to cut above 100 ipm. What is everyone opinion of the C7 Rolled screws from Automation for Less?

Thanks,