Z homing error
Why did the Z homing give up before reaching the load cell? For some reason after loading the filament after power up, the bed goes to nearly max Z. But the homing routine doesn't know this? This is about the 4th time this has happened to me. Z homing screen of death fault. The homing routing faulted before raising the bed to zero. The bed was only half way up. But the Homing Z fault claimed is load cell error. It is not a load cell fault! The load cell will never actuate if it isn't touched. Since the bed was never raised to 0, the load cell did not actuate.
So is there a solution for this? My opinion, this is a bug.
RE: Z homing error
Sorry if I was crabby the other day, but a 30 minute print turned into a 2 hour episode.
Killing the print, and the printer prematurely doesn't seem like a way to foster a good printing experience. Anyone else run into this kind of issue? Where the printer gave up before it should? I understand if it has a problem, it should stop and ask for assistance, but declaring a irreconcilable system fault when there was no need is extreme. Especially if it requires a full system reset. That's just not right.
It didn't find the load cell, because it never raised the bed high enough. I watched the sequence right up to the red screen. There was nothing from preventing the bed from going up further. It didn't stall, it just never raised it high enough.
I can speculate that it lost count, or somehow lost it's way, but I don't actually know that. I do know it gave up and pulled it's own fault. I think it was premature, because the bed was about 100mm from the top at the time of the Red system fault.
RE: Z homing error
Hi,
maybe read up on "trapezoidal nuts", how to align them, the possibility of lubricating Z-axis spindles. I suspect it's a fairly new printer, and if so the problem tends to improve as the printer is "broken in" (= the Delrin surfaces are worn smooth).
Note, it's not completely a failure mode I've experienced myself so I'm extrapolating, might be wrong.
RE: Z homing error
I've never heard of needing to lubricate delrin, never mind on trapezoidal nuts. I don't even know what lubricants are compatible with delrin. To my knowledge, delrin is self lubricating. The nuts spun relatively easily onto the stepper shafts, as I recall. Didn't seem sloppy or tight. I've machined delrin and it's basically slippery. It doesn't tear, at least not with a sharp tool, or decent injection mold.
The nuts were aligned at assembly, how could they become unaligned? Why does this fault only happen the first print after powerup, and no other time?
Two of the nuts were from my MK4S, one from the upgrade kit. Now, I have no idea which is which. Maybe the new one is tighter? But the system never faults if I ask it to do Z homing. Or full xyz homing. It's always
1. After power up
2. Auto filament load by sticking in filament, without even using the control panel
3. During the print sequence
It's a mystery to me.
RE: Z homing error
Well, at the end of the day those nuts may have an issue with friction (arguably from an over-determined geometry, lacking two degrees of freedom to tilt against the print bed). You may be able to resolve it by assembly, lubrication is a possible shortcut (mineral oil should be Delrin-compatible but don't sue me if it turns to dust). If that is the problem in the first place - don't fix it if it ain't broken but it sure is a common problem.
RE: Z homing error
Well, at the end of the day those nuts may have an issue with friction (arguably from an over-determined geometry, lacking two degrees of freedom to tilt against the print bed). You may be able to resolve it by assembly, lubrication is a possible shortcut (mineral oil should be Delrin-compatible but don't sue me if it turns to dust). If that is the problem in the first place - don't fix it if it ain't broken but it sure is a common problem.
Suppose you are right about the friction. I'll try some kind of lube first and report back.
RE:
Just for the record, I'm not sure whether lubricating the Z-axis rods follows official recommendations (at least when I built the printer they said "do not lubricate").
The downside is, it'll attract dust. But those rods are accessible, nothing a brush couldn't fix IMHO. And it might take only a drop to bridge the time until surfaces are worn smooth from normal operation.
RE: Z homing error
Reading on various machining forums, the consensus is that Delrin is pretty inert. One can use oil or grease on it and it doesn't care. Car people use delrin bushings in suspensions and use grease on them to avoid squeaking. People use delrin nuts on acme thread lead screws with oil. White lithium grease is also used. The biggest problem is just avoiding contamination of other things. Some use silicone oil. I wouldn't use silicone oil for this, because it's difficult to remove from surfaces, like a build plate.
Might just try a small drop of a light machine oil and see what happens.
Standard delrin has a low coefficient of friction. There's a version of delrin that has teflon in it, whose coefficient of friction is even lower. Basically delrin is a perfect match to this application.
RE: Z homing error
Reading on various machining forums, the consensus is that Delrin is pretty inert. One can use oil or grease on it and it doesn't care. Car people use delrin bushings in suspensions and use grease on them to avoid squeaking. People use delrin nuts on acme thread lead screws with oil. White lithium grease is also used. The biggest problem is just avoiding contamination of other things. Some use silicone oil. I wouldn't use silicone oil for this, because it's difficult to remove from surfaces, like a build plate.
Might just try a small drop of a light machine oil and see what happens.
Standard delrin has a low coefficient of friction. There's a version of delrin that has teflon in it, whose coefficient of friction is even lower. Basically delrin is a perfect match to this application.
If you want to have an interesting challenge, try printing Delrin (POM). I’ve successfully printed bushings with it. Wasn’t at all easy (that was the fun part).