Z motor grinding when hot


When doing a big job (Starwars calendar) both of my z motors get very hot but one of them struggles to raise itself until I turn off the Lowrider and let it cool down. Has anyone had any experience with heatsinks? I’ve seen somewhere where someone used 12v fans but looking for a quick fix.

A cheap box fan placed where it’s blowing on the motors?

If the motors are running that hot, perhaps the current is set too high. What is your electronics and firmware setup?

I got the motors from v1 so thinking NEMA 17s? Rambo 1.4 and the community firmware for dual endstops.

The V1 formware should have the motor cutrent at 900mA IIRC.

This should be OK. Some.airflow would be helpful of course. Check that it is not the driver chip overheating causing the problem.

Also make.sure that you have lubed the Z screws, and that you have the Z axis aligned well. Some people have mangled the Z alignment with putting parts on the LR2 the wrong way around.

At least you are not damaging the motor with “grinding” – stepper motors do not use gears at all, what you are hearing is just the armature skipping from one set of magnetic positions to another. It sounds horrendus but is not destructive. (A little harder on the shaft bearings, maybe.)


Hi, good news about not damaging the motor. The LR2 is inside a 5 x 7 soundproof enclosure so hopefully it’s just airflow. I’ll check the settings just in case the current is wrong.

What do you think about heatsinks?

If the enclosure is a major factor in the overheating of your motors, then I’d be concerned about the enclosure getting hot enough to soften the PLA parts. I used hardboard insulation as an attempt at sound dampening in my enclosure, and when using my machine on hot day, I found my belts sagging and my PLA truck “wings” (where the steppers mount) a bit soft.

I see no issue with heatsinks, but my concern here is something else is going on. Heatsinks should not be needed. The kind of problem you are outlining is not one we see on the forum from a stock build. Note that for the Rambo board, the stepper motor current is set in the firmware using something called digipots:

#define DIGIPOT_MOTOR_CURRENT { 138,138,138,138,138 }   // Values 0-255 (RAMBO 135 = ~0.75A, 185 = ~1A)

So, your current is set at about 0.8A, which is a safe level for V1 purchased stepper motors.

Motor current is set to .75a in pins_rambo

Karlis Zakitis on YouTube has made some heavy duty z motor/tube mounts so I’ll print them off for backup.

I’ll order some heatsinks and lube. I have been into my shed and noticed that the lead screw wobbles slightly as it turns so that can’t be helping.

I snapped a glued in pin in z1 so moved it to the spare z port, would the pin that’s still in the z1 cause issues regarding current? Just a thought. Forgot to mention that I’m using 1.5,kw spindle so weight?

Thanks for all your ideas, gave me something to work on. I’ll post solution if and when I sort problem out

Motor current is set to .75a in pins_rambo

The value in pins_RAMBO.h are “backup” to make sure reasonable values are initialized. For the V1 maintained firmware, the values are taken from configuration_adv.h. They are set to 138, so only slightly above the default values.

Forgot to mention that I’m using 1.5,kw spindle so weight?

Maybe. If you are not using one already, you might consider 1-start lead screws. They increase the torque by 4x, but impact the maximum federate for the Z axis. This would help with any potential lost steps on the Z axis, but I’m not sure it will help with the heat. The characteristics of stepper motors are a bit strange compared to “normal” motors.

Hi Robert,

Z1 was having trouble raising even when not hot (far worse when hot as mentioned) so I moved the coupler down about 10mm off the motor shaft and it seemed to do the trick so something is off.

You are correct regarding the 138 values.

I’ve ordered some heatsinks and lube so hopefully this will help with the heat,

One strange thing just happened when flattening my bed. Created a 4mm depth box in Aspire with 2 passes and half way through the first pass the flattening bit started to create a ski slope in my spoil board. No idea why as it’s never happened before, checked the g-code in a viewer and all looks good. I’ve moved the coupler up by about 5mm to make sure it was connected to the motor properly so I’ll do it again and see what happens.

If by ski slope, you are referring to sculpted lines where one side is a bit deeper than another, then you might want to check the tram of your router. Tramming adjusts the router so that it is perpendicular to the plane of travel. There are simple tramming arms that make checking tramming easy. It is strange that it only happened half way through your job.

@ste_uk, thanks for sharing details about your sound proofed (very good heat insulating?) enclosure in LR2 build (UK) - #5 by ste_uk

Ski slope as mentioned

A few ideas about the cause:

  • Bit not tight in the collet (fits the evidence best)
  • Overheated stepper driver shut down
  • Mechanical issue like the grub screws on the lead screw coupler (unlikely with this specific behavior)
  • Intermittent wiring issue (also unlikely)


Z wasn’t dropping when Rambo powered off so I lubed the leadscrews and z dropped smoothley so thinking the overheating was no lube. I’ve blown out the Rambo and the LR2 with compressed air and put heatsinks on the z motors also so tomorrow I’ll re-run the gcode to see what happens.

I’ll look at installing a 40mm 12v fan onto the Rambo enclosure also just in case, only problem is that I think the only 12v I had spare on the Rambo is used for the laser.

The best solution would be to hook up the fan directly to where you bring power to your Rambo board. There are other choices. There are plugs for fans on the Rambo board. They are off by default, but can be turned on using M106. The g-code can:

  • Automatically be added by your CAM or g-code sender using their start section
  • Automatically turned on when your electronics are powered up by placing a specific auto-start file on your SD card
  • Hooked up to a custom button in Repetier-Host so you can click it on

There are some 12V pin pairs on the Rambo board, including the ones I frame in red here.



Thats the connection I use for the laser. Good idea about using the Rambo power input, I’ll order a fan and connect.

Hi Robert,

Thanks for your help. I have installed a 40mm fan conecting it to the Rambo power in as you suggested, skirts the length of my table to protect the leadscrews from dust and the z motors aren’t getting hot after I installed the heatsinks and lubed the leadscrews so after skimming my spoilboard I’ll give the Starwars calendar another go.

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Hi, Aaron, if the CNC has been going for a while and I open the enclosure I do get a waft of warm air.

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