Horizontal areas on bed at different heights
Hardware: Prusa i3 MK2, extruder is self-printed MK2S design and standard bearings have been replaced by Igus bearings.
Firmware: v3.1.0
For the first time in several months I did a print that covered most of the bed. On the first layer I noticed that there was a ~1cm strip towards the back (y=160 to 170) and ~2cm strip toward the front (y=20 to 40) that the bed seems to be at a different height than the rest of the bed.
Picture
As you can see in the picture, for the strip near the back it appears that the bed is ~0.1mm or so too high, and for the wider strip near the front it appears the bed is ~0.1-0.2mm too low.
Whatever is causing this is consistent, it's happened on both a PLA print and ABS print (the picture shown). I looked closely at the Z-axis while it was passing over those areas and nothing strange happened, so it's not an issue there, so I assume it has to be the bed itself.
Any ideas what might have caused this? To fix it do I need to replace the Ultem sheet?
Re: Horizontal areas on bed at different heights
Hi Derek, does this happen on every print, it just this G code?
looking at the Bed, there doesn't seem to be a variation in the bed height so the varying thickness seems weird
if you run your finger across the plastic from front to back, is the surface smooth? or can you feel the surface change where the plastic is thinner?
I suspect that if you run your finger across the PEI between the printed pads, that the PEI will be smooth,
I suspect the plastic pad surface will be lower where the plastic is thinner.
if this is the case, then the issue is probably in the G code... or the STL not the heatbed
why is it doing this?
I have no idea,
what slicer are you using? can you share the STL and Gcode?
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
Re: Horizontal areas on bed at different heights
Sure thing. Here is the STL file, and this is the gcode I generated using Slic3r Prusa Edition v.1.38.6-prusa3d-win64.
This issue happened on those files above, and with a very similar one I tried last night using PLA: STL and gcode.
Both looking at the bed with reflecting light and feeling it with my finger, as far as I can tell it doesn't seem to have any different thickness. I'll have to re-run the print to see if the plastic itself feels smooth or seems to have a lower height, I went ahead and let the print finish since it seemed to be OK after 2-3 layers later.
I was also thinking I could make a simple STL that's just 9 0.2mm thick squares spaced around the entire bed to see if the problem duplicates itself again with a completely different STL. I could also slice it with Cura instead of Slic3r to see if that makes a difference.
Re: Horizontal areas on bed at different heights
Would this file help?
https://www.thingiverse.com/thing:2153065
I printed thr first layer of your G code on my mk3, no sign of those two bands on the print!
my mk2 is busy at the moment so can't try that yet!
Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
Re: Horizontal areas on bed at different heights
Thanks for giving it a try. I'll try the 1st level of that test print you linked to, see if it still has the same problem.
Re: Horizontal areas on bed at different heights
This is months later now, but I figured out what the problem was.
I haven't been able to work on it for a while, but yesterday afternoon I set aside time to try and work on the printer again. I needed to re-adjust the PINDA probe and then re-calibrate the Z-axis, but when the y-axis tried to move home the movement stopped and the belt started slipping. I immediately powered it off and turned it over to investigate.
It turns out that when the diagonal arm at the corner of the y-carriage was passing over the end of the end of the y-rod, it was hitting the zip tie that holds the y-rod in place. I think it must have been doing this for a while, because I have often heard a 'thunk' sound from the printer at this location, but have never been able to ascertain what the cause was. It must have gotten worse though because instead of just bumping it a bit it was now completely stopping the printer.
So what had been happening was even when it wasn't stopping the y-axis, as it hit and ran over the zip tie it would slightly raise the y-axis, causing the entire bed height to change slightly. It was doing this at both ends of the y-axis as well, causing the two horizontal stripes on the bed that were different height than the rest of the bed.
I think to solve the problem completely I will need to print some kind of mount for the bearings to attach to the y-carriage, since that distance needs to be increased to keep the y-carriage from hitting the zip ties. But I can't print anything without a working printer (I don't have a backup), so as a temporary fix I wrapped the y-axis bearings themselves with a couple of zip ties and made it as tight as I could. This makes the y-carriage sit a little higher on top of the bearings, which creates enough clearance that the y-carriage doesn't hit the zip ties at the ends of the y-rods anymore.
For a more permanent fix I'll need the y-carriage to be mounted higher above the bearings than sitting flush with them. There are several y-bearing mounts on thingiverse, so I'll try printing this, this, and this to see if any of them do the trick.
Re: Horizontal areas on bed at different heights
Hi, the head of those zip ties should be down at the side of the support legs and with the rods fully inserted into the top of the supports your bed should be nowhere near the zip ties. Worth rechecking the whole geometry of the y-axis again.
Bill
Tagaytay City, Philippines
Founder member of Philippines Prusa Printer Owners FB Group
Sponsor Pillars of God Academy in Bacoor
Re: Horizontal areas on bed at different heights
The zip tie heads are off to the side, just as they should be. I honestly don't know why there isn't enough clearance, there just isn't. Maybe the holes in the y-carriage that the bearings sit into are wider than they should be, causing the bearings to sink in too low and reducing clearance? That's the only thing I can think of that would make that height too small.