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philip

UM Original - Friction and do not printing circles

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Hi everyone,

I printed very well for few months but now I got a technical problem and I am at a dead end on try to solve it. Probably the problem has been triggered when I tried to printed a big architectural model, almost the size of the building volume, I left the machine working alone and it went out of control at one point printing in the air for 2 hours. I didn't design that object and unfortunately I wasn't able to check properly the file, it was water tight but probably not the best file to be 3D printed.

First of all, have a look at the pictures of these samples that showcase very well the issue. IMG 4652IMG 4651IMG 4650photo5photo4photo3photo1photo2

The blue one is the one that I printed before when the printer was working properly. the black ones are the latest that went wring.

In the last picture you see the black one that is not circular. From my knowledge, this can happen when the short belt of one of the motor (in this case the one that is moving the X axis) is not tight enough. It has happened before so I tightened more, however what has happened is on the second picture:the object is circular but at one point during the print the extruder slipped and started to print in another position causing the dislocation of the last part of the printing(this has happened also during the printing of the big architectural model). As far as I know this can happen when there is too much friction on the axes. This is actually happening: when I am trying to move by hand the X axis it is not smooth at least as the Y axis.

I moved the pulleys and tried different positions but it seems nothing is going better. The short belt of the X motor was touching the wood wall but I moved the pulleys and now is the belt is tight and doesn't touch the wood panel, however the problem persists. I checked all the pulleys and they are strongly tight to the rods. I made some videos, if you want to have a look for looking at the behaviour of the machine here the links:

 

 

 

 

I had already done this checks and fixing:

-the short belts of the motors do not touch the wood panels

-all the pulleys are tighted to the rods and they are not slipping during the printing

-the pulleys are aligned to each other

-the belts are tighted

Let me know if you spot anything wrong and if you need more pictures or infos.

Thanks to everyone will take the time for helping me.

 

 

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Wait for others to respond but the first thing I noticed is that the belts are twisting. I think this is due to the pulleys not being aligned causing the belt to ride to one edge and then it rides up that edge slightly.

Not sure that would cause your problem because your problem looks very consistent.

However, to fix, loosen the pulley on one end of the belt so it can side on the rod. Then move the carriage towards the pulley and see if the pulley sides a little. Then tighten the pulley in (I assume) its new position then repeat for the other pulley on that belt. Then repeat on the first pulley then on the other pulley. The object of this is to get the pulleys exactly inline with the point that the belt is attached to the slider block.

For the short belts, loosen the pulley on the rod, make sure the pulley has some space on the rod between the long belt pulley and turn the stepper motor pulley and hopefully you will see the pulley on the other end of the belt slide some.

Make sure you tighten everything.

 

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So many things to say...

1) If your short belt used to be touching the wood until you tightened that short belt I would definitely add 1 washer to each spacer to move the stepper slightly farther from the wall. It might not look like it's touching but you can tell because the short belt twists different directions when you change directions on the X axis. Just do this. This usually causes gradual shifts - not sudden shifts like you got but still - just fix it. Takes 10 minutes.

2) Long belts should be pretty loose. Short belts much tighter. If long belts are too tight it increases the resistance significantly. If you watch Erik's video he has the musical note showing the tension accurately so you can tweak yours like his. Mine are pretty damn loose.

3) The non-round circles is usually caused by backlash aka play. But this can be caused by too loose belts (head doesn't get pulled all the way because the belts are floppy) or too much friction (when axis stops moving belt is still pulling hard (ish) but head is done moving due to high friction. Feel the friction of your head movement with stepper power off. You should be able to push very easily in X only with one finger on each block.

4) You had a sudden shift when printing the black part. Sudden shifts are usually (but not always!) caused by slipping set screws. You kit should have a spare set that are silvery/shiney. These are pointier than the black ones that come with the pulleys. I still use my black ones and they are fine but I tightened the hell out of them. Especially the 2 on each axis on the short belts (motor and pulley above). The short belts take all the abuse. If you are too lazy to tighten these because you don't beleive me the least you can do is take a permanent marker and put a mark on the shaft and pulley. That way if it happens again you will know for sure.

Sudden shifts can also happen due to friction and gcode wierdness (very rare though). Especially if Z axis moves when X an Y moves (Marlin still has a few bugs that almost never show up). Of course in this case they always happen in the same exact spot of the model/gcode.

 

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I had only watched the second video when I posted above. Watching the first video...

g I noticed is that the belts are twisting.

I see that the X stepper belt is definitely twisting. So even though it doesn't look like it's touching the wood - it is. Take that stepper out and make sure the pulley is as close to the motor as possible without touching (.5mm is good) and then add the 4 washers (one for each screw) under the plastic spacers that I mentioned above. Afterwards you will see the X short belt is no longer twisting. And you will get lass black powder below it. :)

 

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Guys thanks for your answers!

I am from UK. I am going to check and make the adjustment you suggested me.

I can already tell you that when I mounted my UM Original I replaced the black screws in the pulleys with the silvery/shiney and I had tighten those as much as possible. I also made markers on the rods for checking if they were moving during the printing but it was not happening.

I am going to change the alignment of the pulleys, I'll let you know how it goes.

Thanks!

 

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Ok, we are getting better.

photo1

In this picture the object at the top is the last one I printed, the one at the bottom is the correct one that I printed two months ago before the arising problem. It's still not rounded but it's better than the black ones and others that I printed in the meanwhile.

- I added the washers to the screws of the X motor and now the short belt is not twisting and is not touching the wall

photo4

photo5

- I moved also the pulleys on the rod connected to the x motor and I think the long belts are not twisting too

- my long belts are also loose and the sound that I can hear is similar to the one in Erik's video

- the sudden shift that has happened with the big model was probably caused by gcode weirdness as you said and as was my concern that that model was not correctly designed

- your point 3, gr5: here we are. I am not able to move very easily the header with one finger in each block. The thing is that I have never been able to do it, even when I was printing properly well. However the movement on the X axis is less smoother than when I push the block on the Y axis.

 

Probably the problem is here, but I am sure the pulleys are aligned. My concern is that the wood panels of the headers are not perpendicular each others and I need to dismount the extruder. Do you think it is the case?

photo3

photo2

Thanks a lot for your help!

 

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I also made markers on the rods for checking if they were moving during the printing but it was not happening.

 

Then the motor must have missed steps. It takes a lot of friction for the motor to miss steps.

I don't know where your friction is coming from but you need to experiment with power off until you find it.

 

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Hi Gr5,

I did experiment with the power off, moving the head by hand and I need to force this movement,it's not happening easiky.

I saw in videos that people can move the blocks with fingers without any pressure but it has never been my case.

After I built the printer, I had been in contact with Official Customer Support of Ultimaker and they told me that since the printer was working fine anyway, it wasn't so a big deal.

Indeed it has worked fine since that episode with that big model,even without smooth movement of the header and with the short belt touching the wood panel.

After the episode, I dismounted pulleys,rods, X motor, I made all the changes suggested me but there are still problems:

-I didn't experience missed steps or sudden shift, but I printed just that small object in the picture

-however it doesn't print rounded objects correctly

- the short belt doesn't touch the wood panel anymore

- the belts, both short and long, do not twist

- the pulleys are aligned and tighted to the rods

- the movement of the header is still not smooth but I need to force it

My concern is that there is something damaged or broken, I don't know a bent axis?

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I didn't see if you'd checked the end caps over the axis rods? If those are screwed too tightly, they can stop the rods rotating as they need to.

You might also need to square up the cross-rods through the head. To do that, undo diagonally opposite pulleys on one of the axes. E.g., front-left and back right, on the x axes. This allows the two long belts around those axes to move independently of one another. Move the head all the way to the back, making sure both sides of the cross rods are an equal distance from the pulleys. Then tighten the front pulley back up. Move the head all the way to the front, making sure its still square, and tighten the back pulley. Then repeat for the other pair of axes. You might also need to loosen the tensioner/screw in the sliding blocks, to make sure that the cross rods are fully seated - if they aren't you can end up with the exposed part of the cross rod being too long - and that can also push things out of square.

 

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