Loosing steps on x and y

Mostly Printed CNC - MPCNC Troubleshooting
#1

Hi,

I did my first cut in 16mm mdf at 20mm/s feed and 1mm per pass. on about the 10th pass both the x and y started skipping and machine jammed.
I tried different feed rates even as low as 10mm/s with varying results. Sometimes jamming, and sometimes not.

It is almost as though the x and y steppers are not as strong as I had thought they would be, which got me thinking.

My stepper motors have a current per phase of 2a, so that would be a vref on the DRV8825 of 1v (I have heatsink and active cooling on drivers). This would be ok for the z, but does this mean that the x and y motors only get one amp each? Is this why they seem under powered?

Cheers,

Damien

#2

Are your drivers overheating? are you using the new software shown on the first page?

If you really think you need more power, you can wire them in series and double the power.

I use the same steppers to pull the lowrider around and have never (literally never) skipped steps on the mpcnc and I have 3 of them running all kinds of things. All these new posts about skipped steps are kinda weird. This has never ever been an issue in the last almost 2 years, and we are now using much stronger steppers, wires, and better tuned firmware.

I seriously think something else is the problem. could be anything but I would suspect lack of power to be the very last thing to worry about. Your gcode, your cam, your bit, your spindle, your vacuum causing noise or power issues, it has never been lack of power.

#3

That might have seemed a bit harsh. I did not mean it that way. I just mean assuming it is lack of power I think is the wrong assumption, I feel it is a symptom. If you truly think that is the issue please answer the questions in the sticky.

All the details of your machine are needed. What are you using and where did you get it. anything other than standard software or hardware, what size, ect…

And to answer your question more correctly yes 1v would max out the z axis and half power to the xy in parallel, max in series. You should not run steppers at max power, you will melt the plastic it is mounted to. It’s kinda like redlining a car, you can do it but not for long, steppers that are run that high are run in spurts not continuously. When running continuously you need to turn them down a bit.

#4

Hi,

Am I correct about the drivers though. Is the current being halved between the 2 steppers? Are my motors too big for those drivers?

I am using this version of firmware B16_32_8mm-fullG-112515, along with latest version of Estlcam, setup to how you suggest.

I am using this spindle http://www.ebay.co.uk/itm/CNC-400W-Spindle-Motor-ER11-Mach3-PWM-speed-controller-Mount-engraving-set-/272220155079?hash=item3f6195ecc7:g:U~EAAOSwT6pVxVxR
It has a max rpm of 12000

And I am using a 4 flute 3mm end mill.

What feed rate should I be able to get before loosing steps?

Can you recommend a bit to use? ie. 2 or 4 flute. And would the cutting depth of the bit cause the machine to jam?

thanks,

Damien.

#5

You need to update to RC7 firmware.

A two flute endmill max, because of the high rpm spindle.

Movements are discussed here, https://www.v1engineering.com/software-updates/

Drivers questions are answered above.

#6

That spindle has less power than the 660 so expect to move a little slower or a little shallower.

#7

I would expect your skipped steps to be caused by that 4 flute bit overheating and dulling or sticking to the material. Proper feeds and speeds take very little power to move a bit through the material. The first videos I put up were a flex shaft dremel wit tiny steppers, and a much less rigid machine, milling aluminum. Gcode is 95% of the cut.

#8

Hi,

Thanks for quick reply’s. Is RC7 compatible with 8mm threaded rod?

So what would be a good percentage to run steppers at 50%, or 75%? Would like to get most out of them as I can without damaging them.

Thank you for your help,

Damien.

#9

You are using a 8mm rod? You will need to change the z axis steps, and acceleration. I don;t have those numbers I don’t have one to test.

I set the drivers to .7V wired in parallel with the steppers I sell. Every stepper is different.

You haven’t really given any details about your machine so I can confidently answer much. are you using drv8825, what steppers, how are they wired, what size pulleys, how big is the machine. These are some of the questions in the sticky.