selftest error! please check: axis length Y  

RE: selftest error! please check: axis length Y

Hi Rich, 

does the Y Axis move freely backward and forward by hand, when the printer is  off or at standby?

being unable to see the printer and play with it, I am largely guessing.
the Mk3 does not have physical endstops, on X and Y Axis, it relies on the printer X and Y sliders coming to a halt when they hit the ends of travel being reported by the stepper motor drivers and then treats these points as virtual endstops. the problem is, that if something causes the Sliders to stop early, the length of the available travel is short causing the error

you have already tried a number of valid tests, so the next things I would suggest are 
Is the cable bundle from the heatbed, catching on the frame?  Is the cable bundle from the X axis catching on the heatBed
Is the Y axis Idler free to rotate at the front of the frame? 
Is the Y Motor Toothed wheel too close to the Y Motor mount, at the back of the frame? 
Is the Y Motor itself rotating freely (there should be a regular slight resistance when the motor turns, but no tough sections)

Prusa uses single bearing idlers on the X and Y axis belts, and I Have had these fail, in the past. 
I Now use twin bearing idlers   (And as a matter of interest PRUSA now supply twin bearing idlers with the Mk3.9 and Mk4 printers)  I got mine off Ebay
Hope this helps, 

Joan

RE:

Hi Joan thanks for the reply. I'll attach links to two videos below.

Video 1 (Moving the bed by hand) Video 1
The bed moves freely but there is some resistance. I assume this is normal? I would assume it shouldn't slide effortlessly along the rails. This was done while the machine was plugged in but turned off. Not sure why the screen flashes while its off.

Video 2 (The self-test process beginning at the x-axis calibration) Video 2
The amount the bed moves in the y-axis part of the calibration varies every time I try it. Sometimes the bed moves back and forth the full length and then still says there is an error. 

Is the cable bundle from the heatbed, catching on the frame?
No.

Is the cable bundle from the X axis catching on the heatBed
No.


Is the Y axis Idler free to rotate at the front of the frame?
Seems to move fine when I move the plate back and forth.


Is the Y Motor Toothed wheel too close to the Y Motor mount, at the back of the frame? 
I'm not sure what too close is. I've attached two images of both ends of the y-axis belt if that helps.

Is the Y Motor itself rotating freely (there should be a regular slight resistance when the motor turns, but no tough sections)
Seems to be rotating fine. There is some resistance when I move the bed but I would expect a small amount of resistance. There are no points where I feel like a certain point is being obstructed.

RE: selftest error! please check: axis length Y

Also, the machine will not recognise the SD card when inserted, the card is recognised when inserted into my laptop so I don't think the card is the issue. I've cleaned the SD card slot and no change.

How is the SD card formatted?  It has to have a FAT32 filesystem on it.  It also can't be locked.

RE: selftest error! please check: axis length Y

Hi Rich, 

It does look like the Y axis is stalling as it moves backwards. 

Have you tried Auto home, on the LCD Menu? 
does that improve things? 

If autohome works, can you use the Move Axis Y axis option  on the LCD under settings, I think, 
can you move the whole 210mm?

If you physically move the Y axis platform to the back and try again? does it still error?

regards Joan

RE: selftest error! please check: axis length Y

Hi Jim, thanks for this. It wasn't formatted to FAT32, I've now done that and the display has changed from not recognising it to reading 'Print from SD'

RE: selftest error! please check: axis length Y

Hi Joan, the autohome doesn't seem to help. I ran it and then tried calibrating again and it failed.

I used the 'move axis' setting, starting at the very back position it moves +212mm to the very front.

I physically moved the y axis bed to the back and it still errors when I run the calibration.

RE: selftest error! please check: axis length Y

I should mention that when I lubricated the y-axis rods originally I used WD-40, I don't know if this is right or wrong as I've seen contrasting opinions online. I did buy some sewing machine mechanics oil today if that could possibly be a better option.

Much better.

The recommended lubricant is a light grease which lasts longer before relubrication, Prusa sell small tubes that contain enough for the life of the printer but before they released it I used to use a light machine oil similar to sewing machine oil.

There are aerosol lubricants on the market that would work (don't do it, there's too much chance of airborne oil going where it shouldn't) but WD40 is not a lubricant and doesn't pretend to be, 'WD' stands for 'Water Displacer', it is intended to drive out water, free stuck mechanisms and loosen rust.  Sometimes it dissolves excess lubricant that has been displaced by a mechanism and allows it to seep back in but the proper use of WD40 is to use it to free/clean working parts, wait a few minutes, then lubricate with the correct oil or grease.

Cheerio,

RE: selftest error! please check: axis length Y

Wd40 is for heavy duty, mechanical parts. For 3d printer use something soft, oil like greases, like for some chains. Probably even hi-end, bike chains lubricants would be ok. 

RE: selftest error! please check: axis length Y

Wd40 water proofing spray is not a good idea for 3d printer, wd40 white lithium grease on the other hand is good 

RE: selftest error! please check: axis length Y

I ordered some white lithium lubricant online and lubricated the y-axis rods again. I also loosened the y-axis belt a bit more. It runs through more of the y-axis test but ultimately still fails. Any other suggestions? I really do appreciate the help btw! Video

With the power off, move the axis by hand; is it smooth? Does the resistance stay the same over the whole range?

Carefully tip the printer on its side, move the axis by hand again, watch the underside and see if anything is hitting the frame at the ends of the run.

Check the smooth rods are not damaged/scratched. Check the idler pulley is not clogged, out of line, or damaged (loosen the belt and try turning it with your fingertip, is it smooth?)

With the belt loose try turning the stepper motor by hand; is it smooth through a full rotation?

Cheerio,

RE: selftest error! please check: axis length Y

thanks Diem, it turned out that the bearing at the front was too tight so I loosened the screw a bit and it was able to get through the entire calibration, thanks for all the suggestions guy!