Crashes during start of print calibration.  

RE: Crashes during start of print calibration.

I should add that it was working perfectly and has not been moved or changed in any way that I know of.

RE: Crashes during start of print calibration.

Hi Sam, 

I think you are Absolutely Correct, the Printer literally doesn't know where Home is.

the Mk3 Printer does not have any endstop switches on any of the Axis' 

For X and Y it relies on the stall current of the motors when the carriage hits the end of travel...., creating a 'Virtual End Stop'

I believe you will find that the Y axis does not move freely backwards and forwards.   Probably because there is NO Lubrication in the Linear Bearings. 
this can cause excess friction in the Y axis motion, which makes the printer think that it has reached the end of the axis motion, when in fact the axis has only moved a couple of millimetres. 
there are other issues that can cause this problem, such as Ubolts too tight, cables snagging on obstacles, excess belt tension, idler bearing breaking down, Idler bearing  mounting screw too tight, Y motor belt pulley rubbing on the mounting bracket....     but these normally show up, just after assembly.. 

if  you have some 3in1 oil or similar, put a few drops on each of the y axis smooth rods, and work the bed back and forward a number of times to see if it loosens up.
if oil loosens it up,  I suggest that you schedule a maintenance period for some time convenient. 

regards Joan

RE: Crashes during start of print calibration.

@joantabb

Hi Joan, thanks for your suggestions.

That solution doesnt make sense to me though as the Y axis moves freely and it has no trouble hitting the end of travel. 
The problem seems to be that when it hits the end of travel it doesnt recognise it as an end stop but it keeps trying to move further.

What do you think?

RE: Crashes during start of print calibration.

There are two ends to the Y axis. The video seemed to show the priner with the bed forward. Then the  printer starts and the y axis fails to home to the back of the frame. It does the first row of mesh bed levelling across the back of the bed instead of the front of the bed. Then tries to move the bed forward. However the bed is already nearly all of the way forward so the bed hammers against the endstop and mesh bed levelling fails...

Your printer. Your choice... if it was my printer i would be wondering why the bed is not homing properly on the Y axis

Regards Joan

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RE: Crashes during start of print calibration.

@joantabb

Yes I am wondering this.
Maybe I didnt phrase my post properly.
However I don't know how to resolve the issue. 

RE: Crashes during start of print calibration.

OK I think the issue is the Y-Belt is slightly loose.
So I suspect what is happening is that when it is attempting to hit home position the belt slips on the teeth and the steppers dont see enough resistance to register as end of stroke. 

RE: Crashes during start of print calibration.

the End stop notification is increased resistance to travel. causing increased motor current! when the Y carriage either hits the back endstop (Belt clamp collides with Motor mount, IIRC). or if there is significant friction... due to unexpected mechanical problems. 

I wouldn't expect a loose belt to cause this issue, but If tightening the belt works, then you have resolved your problem