Homing feedrate in Z slower than in X and Y - why?

Dear Snapmakers,
is there a reason why the homing is running a slower feedrate in Z-direction as compared to X and Y?
Thanks for any insights!

The z axis has a larger load than x & y, it has to lift the whole x axis plus the print head. That extra load means it can’t move or accelerate or decelerate as fast as the X & Y.

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@Tone: Hmm, I have difficulties believing that this would be the reason. In Luban I can set the feedrate to 3000 and move Z at this rate - the printer has no probems with that. And while I agree that Z has to lift a bit of weight, it is still nothing the steppers would break sweat about. Y has also move a bit of weight: the print bed. And: If you consider milling, the torque and forces that come up there are larger than that I´d say. And you can see how powerfull the steppers are: While Z is homing, you can put your arm on the horizontal linear module, and even press it down a bit, the machine is totally unimpressed and does not skip a single step.
I must say, that Snapmaker airs “I am robust, hefty and powerfull” at every point! And it must for later carrying a 710W spindle as shown in the live stream.

So, long story short: I still need to hear why Z is slower while homing :slight_smile: (No offense, but I think you´re wrong here)

I have tested the fastest that each axis can move. The x & y can move at about 20000, the z at about 9000!

OK, interesting! However, I suppose 20000 is not the homing speed, is it?

After all, it seems that Snapmaker tried to stay on the safe side.

No, it’s not homing speed, but it does demonstrate that it takes more force to move in the z direction. I think I tried some custom homing code and moving faster seemed to affect the accuracy of the z direction calibration. Maybe it has more to do with how fast it hits and then reacts to the limit switch. The z direction is more important than x & y as it affects the first layer thickness. If x or y is slightly off you probably don’t notice it unless you have to restart after a power outage. @parachvte, maybe you could clarify?

BTW, seeing it move at 20,000 is pretty impressive, but it does struggle to move in 2 or 3 directions at the same time and keep it an accurate and synchronized move.

I certainly will try this when I´m back at my machine next week :slight_smile:

I do have a thread in this forum about axis speed, you do have to change the maximum allowed speed before you can go those speeds. I think everyone’s maximum will be slightly different. Snapmaker has backed way off from those speeds to be way safe. I’m sure they did a lot of experiments before picking the maximums they did.

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I suppose you mean this thread: Speed Limits on SM2? - thanks for pointing me there! If the factory limits of 150 mm/s in the end can be used I am happy, that would be an acceptable speed.

I am still torn between pushing the machine to its limits, accepting potential wear and at some point having to replace the nuts in the linear modules, or accepting the day-long printing times of the “official” limit of 60 mm/s, which - considering the huge build volume of A350 - is disappointingly low. On Facebook a user has pushed his printer, and finally had the plastic nuts worn, and replaced them with brass nuts. I´m curious what he will report on the long run…

Hi Hauke, the Z-axis has more loads than X and Y.

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Thanks @Tracy! Seems @Tone was rigth after all!

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Makes sense. While Y has to move inertia (bed weight), it doesn’t have to lift it against gravity. Mostly Y is only going to be fighting that mass on direction reversals.

Definitely seems like the option to ‘raise Z on non-extrude movements’ would be a wear issue.

Not happy to read about experiences with the plastic nuts and suggestion of brass replacements. Aren’t the leadscrews just zinc-plated steel? Brass might wear the plating down instead of wearing out themselves…hopefully a while before I have to worry about that.