[cncc]

I have a Sherline 5400 mill converted to CNC myself using the Sherline CNC kit. It is working mostly fine now but the biggest problem I currently have is Z-axis slipping. When it is supposed to be holding position while cutting, the Z-axis slips down little by little. It is very obvious because I have hand-wheel attached to the motor shaft and I can see if happen.

The stepper motor has 125Oz-in holding torque. It has good torque. When it goes up at 24ipm, I don't think I can stop it by putting my finger on the spindle and I am a strong guy. The same as it goes down. I thought the torque is the highest when it is supposed to hold steady?

The driver is a 4-axis TB6560AHQ board from eBay. I am running it with 24V power supply.

Anyone got ideas on what may be wrong?

[GeneK]

When you see the hand wheel move does it turn or just move down? If it doesn't turn but only slips down there is backlash in the system. If you have the Sherline stepper mount there is a backlash nut that can be used to reduce the backlash.

GeneK

[cncc]

It actually turns.

I had the backlash adjustment upgrade on z-axis. I checked the backlash it is about 0.001.

[BAMCNC.COM]

Only 24v for that torque? Also what's your current settings, is your motor hot? Are you Z gibs tight?

[awerby]

It sounds like that crappy ebay driver board is losing it. They are notorious for this. If you're an electronics genius you might be able to re-engineer it, but otherwise, just throw it out and replace it with something better. If you get a Gecko G-540, which people here tend to like a lot, you'll also be able to double the voltage you run at, which will increase your maximum speed considerably.

Andrew Werby
www.computersculpture.com

[cncc]

Current is limited to 2.5A due to the board. The motor never runs hot. I cut at about 9ipm (only aluminum so far). The Z gib is pretty tight.

[cncc]

If I can confirm that is the cause...

[cncc]

New finding:

It seems to have something to do with the motor RPM. If I stay below 2000RPM it is OK. It starts to slipp when the motor runs at the upper end around 3000RPM. The interesting thing is, it is not related to cutting force. I had the end mill off the part and the slipping still happened!

Interference problem? The Z axis stepper motor does sit pretty close the the spindle motor. Or somehow the board is affected by the EM interference from the motor?

[cncc]

The problem is fixed after I plugged the motor to another outlet. It appears to be an EMI issue from the Sherline DC motor. After I put in the right keywords many discussions showed up. Somehow the motor noise cause bogus step signal from the controller.

Thanks!

New finding:

It seems to have something to do with the motor RPM. If I stay below 2000RPM it is OK. It starts to slipp when the motor runs at the upper end around 3000RPM. The interesting thing is, it is not related to cutting force. I had the end mill off the part and the slipping still happened!

Interference problem? The Z axis stepper motor does sit pretty close the the spindle motor. Or somehow the board is affected by the EM interference from the motor?

[rcs2022]

I had similar issues on my sherline, but I would usually restart the computer when it happens, and the issue would be solved.