Print head not return home on Front - back axis..

[Schalkdk 1]

Hi Ultimaker Team/Community

 

I'm looking for some advice. I have an Ultimaker 2 extended. 

As I'm sure you are well aware, the normal operation after a print; is for the print head to return home. Then when a new print starts the bed lifts to about 2cm below the print head, and the head will move to the front left and extrude(Purge the hot end) then move to the start of the print, and then start to print the first layer.

 

My printer prints 100% - No problem with printing!

 

My issue is... it does not send the head back home, 

Not after bed levering

Not after a print.

Or on startup

 

When I start a print, what happens is this; the printer moves the head forward as if the "IT believes the head was at the "Home" position Top Left!

But it moves forward then the stepper motor slips the belt "Until IT believes the head is now at the ready point to start the print/extrude/Purge"

The Left to right axis works 100%

 

Then the normal print sequence starts and it prints 100%

 

After the print, it moves all the way to the left but not backwards, it stops at the same level the the print ended at and it does not return home on that axis....

 

What can I check? As mentioned it prints 100% I can post a video if it will help.

https://drive.google.com/file/d/1-6VnxWRQ-lBh14UoNG9h2X5oEjvgG2wA/view?usp=sharing

 

Thanks, Schalk

[MariMakes 192]

Hey @Schalkdk

 

Welcome to the community! 🚀

I'm having some trouble understanding what you are encountering. 
I've checked your video but the printjob doesn't finish so I do not expect to see the homing behavior. 


What you are describing reminds me of a broken X or Y switch as described here.
But than you would see an error in screen.

If this is not it, can you maybe rephrase your problem as:
I see ... but I expected ...

Thank you! 😄

[Schalkdk 1]

Hi Mari. 

 

I'm sorry if I'm not clear. I'll try to give a little more more details. 

 

After a print job finish I ecspect the print bed to drop to the home, (bottom.)

 

It does that. 

 

Then I expect the print head to move all the way to the left and all the way back, default start position. (power on position) 

 

It does not do this.

 

What it does is it only moves all the way left but not all the way backwards.

 

Have a look at the 2 videos named print finishing. And you will see. What happens when the print finish. 

 

I have to manually move the head all the way back to the start position by hand before I start a new print.

 

If I don't move head by hand and I start a new print, the print head moves forward (from the position the last print stopped) and when it reaches the end of travel the steeper motor tries to keep moving further and then the steeper skips on the belt because the head can't physically move any further. 

 

There are no limit switch the determine the front left stop. This is done by stepper-motors steps. In the firmware... I think. 

 

Also if I go into the menu "home head" it does not home the head. Watch the video "home head" and you will see what it does. 

 

I actually press the home head button repeatedly so you can see what it does. It move the head slightly forward everytime. And not to the back. 

 

So for now I have temporary work around. Move the head by hand. Before every print but this is not the way it is supposed to work. 

 

Please let me know if I can explain anything more. 

 

 

[gr5 2,094]

I don't have access to your videos on google.

 

Your words above seem to describe a problem with the stepper motors - they aren't moving when commanded.

 

This can happen if the stepper driver chip is dying or if the chip gets too hot or if the movement is too fast (actually maybe try doing a FACTORY RESET in the UM2 menu system which will reset the speeds used when homing and when the print is complete but this will make you level the bed again).  It could be these are set to an overly fast value somehow.  It could be a bad wire to the stepper or the stepper itself (it's very unlikely the stepper - these tend to be amazingly tough and should never fail in your lifetime but sometimes they do).  It could also be excessive friction - push the head around in X and Y and see if maybe Y has more friction.  Maybe add 1 drop of light oil on each of the 4 outer rods and also the 2 rods going through the print head.

 

It would help to see the video so I can see if it starts to accelerate towards home position and then gets too fast.  If it makes a humming sound but doesn't move then it's probably not the stepper driver.  If it's silent then the stepper driver may have turned itself off for a second (it has a built in computer and thermometer and will shut itself off briefly if it gets too hot).

 

Pushing the head to the front right corner and then doing a XY home would help as then only one stepper should be moving and it's easier to see and hear what is happening.

 

[Schalkdk 1]

@gr5

 

https://drive.google.com/drive/folders/1zkrZQTsJQ6RhzGGn8YvCx8hAAi69s5zp

 

This is the link to the Google folder. 

 

The thing is, the printer prints 100% no issues, so I would think all your ubove mentioned issues will also affect printing not just the homing of the head after the print. 

[MariMakes 192]

Ah! I understand now.

Your problem is that your printer doesn't home over the Y axis.

There is a limit switch here in the back, there is something wrong with it.
It might be disconnected, broken or stuck in a pressed position somehow. 


The switch is not checked during printing, so that is why you can finish your printjobs. 

Can you take a look for us if something is wrong with your switch? Thank you!

[gr5 2,094]

@Schalkdk - I must not have been clear.  Your link takes me to the below message.  I need authorization to see your video:

[gr5 2,094]

If Mari is right then you can push the head and hear that it doesn't click.  Usually the Y switch fails because the rod that goes through the print head is supposed to stick out to the left of the left sliding block and so you might simply need to push hard on that rod a bit to slide it a little to the left.

[Schalkdk 1]

Hi guys. Thanks for the help. 

Together with your help and a bit of investigating I tracked the problem down. 

 

It looks like the wire form the Y limit switch was pinched between the wall and the extruder stepper-motors during assembly, and over time I think the vibrations managed to break the wire, shorting it out it obviously fooled the controller in thinking the the print head is at home whenever the controller checks. 

 

I repaired the wire and the problem is now fixed. 

https://drive.google.com/file/d/12590mUfi3Wl5eNwwnUAsJ05yxbsvBdQv/view?usp=drivesdk

 

[MariMakes 192]

Thanks for the update! I'm happy that your issue is resolved!

For the curious cats, this is what the cable looks like: