Z Axis skipping

So I am going crazy trying to figure this one out. I just rebuilt my lowrider into the V2 because my Z axis motor was skipping when rising. Replaced that motor and rebuilt and now the opposite side motor is skipping when trying to rise. I replaced that motor also to make sure it wasn’t just a bad motor and it is still happening.

When the z-axis goes to rise, it just skips a little, and then keeps working, screwing up my layer height. I have all 84 oz.in motors on my ramps 1.4 and my drivers at .7v. Is that maybe the setup that is causing it? I was thinking maybe switch to a rambo mini might fix it or even changing to the 76 oz.in motors that everyone else is using.

I’ve read a little about the different things it could be. I’m thinking maybe its something to do with resistance in the wiring or something with long lengths of non-shielded wires. I’m a little in the dark about the “ghosts in the machine” so I’m not sure what to do.

My next step I guess is to remove wires from inside the stainless tubes to start to see if I can narrow it down. Does anyone have any pointers? Is it maybe the motors? the board? or the wiring?

Video of skipping:

We use this on 76oz/in and it is a tad low, a quick way to check is if you steppers get warm (not hot) after 10+ minutes of being enabled.

What screw is that. It does not look like the standard T8 we are using it looks to be a finer pitch? To be safe move your Z no faster than 4mm/s to start with. G0 Z25 F240 Does that move exactly 25mm?


Also make sure your T nut is loose, as in do not tighten the little M3 screws all the way so it has a bit of wiggle room.

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There shouldn’t be problems with any of those parts.

Are the drivers hot?

Does the machine move smoothly on its own? Does it drop under it’s own weight?

If you want to debug wiring and your motors, disconnect them at the RAMPS, and measure the ohms across each coil. In series, it should be 2x of just one motor coil, and it should be in 5ish ohm (not 50 or 0.5) range. You can look at the value while tugging on wires, moving connectors, etc. I think I told you before if you have one good coil connection and one intermittent one, it can act like this.

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I believe it is an 8mm pitch, 2mm spacing. I had them from a previous project. I will run this code on lunch and see how it compares.

Ill check but I’ve never noticed them getting too hot. Should i adjust them differently for the larger steppers?

This might be worth looking into for me. I know they drop freely under their own weight when I detached them from the stepper, but maybe just off by enough when attached that they are binding.

More power but also more cooling, above 0.7V and they get stupid hot really fast, so keep them cool. There are equations for the actual number but them temp test gets you close, cold = needs more power.

It can also be your settings and gcode so just run my code before you do anything else.

And also also, make sure your coupler set screws are not slipping.

So I loosened the t nuts and that seemed to help I think. I also found some settings in Estlcam that I hadn’t seen before to slow down the Z axis. I checked the drivers and they did get pretty warm at .7v after ten minutes or so of running. There’s a fan on them always inside the case.

Ryan, running your code raised it 25mm so the drive screw seems to be fine. The whole thing nearly lowers on its own weight when off, but not quite still. Is that still not good enough?

It ran perfectly for an hour and a half cut, perfect layer height on this one:

[attachment file=71184]

On the second file, about an hour in, it skipped again on the same z axis and cut through the engraved area.

I had a similar issue with a 3D printer a few years ago. For me it turned out to be a wireing issue. When the carriage that held the motor would move the wire would move and the harness would slightly change angles. That would cause it to have an unstable connection where it plugged into the stepper motor. It would make some loud noises like it was getting stuck or skipping steps. Then it would resume like normal. It was really hard to track down. I wasted a lot of time looking into firmware, drivers, steppers etc…

In the end I found better ways to secure my motor wires and the problem went away.

Hope that helps.