Originally shared by Jeff Keegan
Need another set of eyes - anyone want to weigh in on my Z-axis problem?
On my Sells Mendel, recently during prints I’ll watch it during a Z-axis move, where it should be going up 0.4mm (about 1/3 of the rotation of the leadscrew), I’ll see it instead barely move at all and make a “eerrrrhhhh” sound. If I don’t interfere (by twisting the leadscrew(s)) the layer will be squashed flat (and I haven’t measured it with a calibration print recently, but I think the last few successful prints I’ve done have probably been shorter than they should have).
I’ve got a few paths to choose from diagnosis-wise, and that’s where I want more people voting on which path to go…
- I tried upping the current on the stepper driver (this RepRap is using RAMPS 1.4), then powering off the RepRap (I seem to remember that the firmware reads the value of that trimpot once at bootup or something, not continuously). That didn’t seem to work, but I may not have turned it enough, or I may have turned it too much.
The problem with going down path #1 is that the failure doesn’t seem to happen when I’m just jogging Z up and down in pronterface… It only happens after a layer of printing. That might be because pronterface is using a different default speed (I’ve set mine way down at 32 mm/min - it can’t handle more than that reliably). Maybe I’ll try using the exact same gcode commands that are in the gcode file I’m printing with and see if I can get a more reproducible test.
- I’m still using Sprinter on this RepRap (unlike my other one which is using Marlin). Last year at Makerfaire when using both next to each other, I told myself I’d upgrade my original RepRap to Marlin too, mainly because there was a bug in Sprinter that if you jog forward too many times in a row (like, hit the +x10 button, then hit it again while still moving) that it’d move REALLY slow for the second move until that move finished.
One thought that had come into my mind was that maybe these Z failures were only after everything was moving super slow due to the Cool module in skeinforge/sfact (this older RepRap doesn’t have a fan yet), and the Z move happened right after that, and was suffering from some similar slowdown (which was causing stunted movement for some reason?).
Anyway, #2 is replace Sprinter with Marlin. While a good move, it might be a huge timesink that doesn’t solve my current problem (and I want to keep my printer working right now).
- Maybe the leadscrews are completely gunked up with crap and it’s physically harder to move in Z. (Though when I jog around in pronterface it works…)… Anyway the thought was maybe the bearings at the bottom are all caked up with metal dust from the leadscrews having worn over the years, or maybe the threads in the leadscrew are just full, etc. I could spend some time cleaning those out, maybe even removing the leadscrews to give them a closer examination (but I really don’t want to dismantle things). I could lubricate it with silicone spray… I could check the M8 nuts at the bottom are still holding firm against the z-driven-pulley. All of this is in the it-phyiscally-hard-to-move area though and won’t matter if the problem is the current or some firmware bug.
Here’s a video of the problem (you can hear the bad turn at 3 seconds in). My guy tells me it’s a current problem, but…
