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somerwil

UM2 curved prints - solved

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Hi,

after some problems with the UM2 I'm now printing for a few days. Did some good print with it which made me very happy. :grin:

Of the initial problems there's one remaining: let's call it "Layer curving".

I had this problem on two prints so far (at least where I could see it ;)).

First part was R2-D2's bottom leg part.

 

 

 

This was previously analyzed by gr5 and illuminarti. They suggested it may have something to do with either material shrinking in combination with infill or the belts being too loose. Good suggestions so I did get some extra tension on the short belts to prevent this effect. I need to adjust the design of R2's part to optimize the shrinking effect but that's something on the list.

Today I started a completely different print: the Eiffel Tower. Alright, a bit ambitious but I wanted to give it a go. :oops:

The Ultimaker did pretty well up to the top of the arches.

 

As far as I know, the Eiffel tower is symmetrical but when you look (not even) close to the picture you can see the layers are 'curved' to the right. This is clearly visible from the top of the arch layer and up.

I could also see this effect on the first few layers of the print but it wasn't too bad there so I kept the print going.

The picture was taken approx. 11 hours into the print and I stopped the print because of this issue.

I can think of some things resulting in these issues but these are rather complex to solve.

Anyone?

Thanks for reading!

Michael

 

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Your X axis is slipping or missing steps. Usually the suggestion is to tighten the set screws (aka grub screws) on the 6 pulleys for that axis. However when it slips such a small amount it is usually caused by missing steps.

Here are some things known to cause this:

1) Power off machine and push the head around - x and y should feel about the same. Try lubricating the shaft or possibly loosening the tighter belt. Personally I wouldn't touch belt tension unless it was twice as tight as the "good" axis.

2) belts rubbing the side. Particularly the short belt between the motor and first pulley.

3) Motor rubbing side of machine.

Some people recently had some kind of movement where the pulley was starting to rub against the outside of the machine. I would take off the metal cover for the "bad" axis (x axis? Right?) and look very very carefully at the belt and make sure it is well clear (a few mm) away from touching anything.

While you are at it tighten the heck out of the tiny set screw in the motor pulley.

 

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I got the vertical white covers off and checked all the set screws in all the pulleys. Also checked belt rubbing (none detected) and relubricated the bars.

I could easily give most of the set screws approx. 1/16 - 1/8 turn. That's quiet a lot I think so I also checked the other, easy to reach screws of the machine. I could give most of the outside screws (that keep the body together) a few turns without getting the feeling to strip the thread. Particularly the acrylic side plates were mounted very poorly.

It's printing again now (not the Eiffel tower ;-)). Fingers crossed. Will give an update anyway.

 

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I could easily give most of the set screws approx. 1/16 - 1/8 turn. That's quiet a lot I think

 

Um. Yes. That's definitely a lot. That was probably it. You got all 6 set screws for the slipping axis? Even both of the short belt ones?

 

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Even though I had some good prints in the meantime the curving problem returned.

Curved layers

The file is on Thingiverse - it's the head part of the loggerhead sea turtle http://www.thingiverse.com/thing:164317/

 

This print is supposed to be symmetrical but obviously it isn't...

I think something is wrong with the steppers since I checked everything mechanical. Should I send a support ticket? Or are there other thing I may check?

Michael

 

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It could be the steppers losing occasional steps, but I still think that it's physical - I just think that if it was the motors it would skip occasionally on long fast moves, and the layers would be misaligned by large amounts, rather than this very gradual layer to layer shifting.

Check the X-axis pulleys again - especially the short belts. If you can use a permanent marker to put a mark on the pulley and shaft, then it will make it easier to tell if they have moved relative to one another.

 

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Ah! Okay - this picture is MUCH more helpful than the previous ones. This is almost certainly lost steps in the motor. That happens when you have very high friction. You are only losing a few steps per layer but it adds up and the print is slanted.

First of all, turn off power and push the head around by hand. It should be about the same in X and Y. Oil the X rod with one (or two) drop of light petroleum oil. Preferably with no additives (WD40 has additives). Push the head back and forth and see if that helps. Also oil the 2 rods that the X blocks are on.

Now more likely issues. The X motor is in the back right corner. Push the head back and forth and see if the short belt there is possibly touching the walls of the UM. If it is touching something it usually twists a bit and twists the opposite way each time you change directions. Some people recently got UM2's where a belt was touching something and it caused this "lean" issue. It was *very* subtle. You might need to put a piece of paper in there to check. Or something like that. You might want to loosen the X pulley on the motor and move it a half millimeter closer to the motor if that's possible. Also check the long belts and make sure they aren't touching anything. Push the head back and forth and look very carefully all up in there at all the X long belts. Also look where the other end of the short belt attaches up at the top. Make sure the belt isn't rubbing. Also check the tension of the belts - if they are too tight this adds tension.

A quick software fix might be to lower the XY acceleration to 1000 mm/sec. I think 3000mm/sec is a reasonable value but I think the um2 comes with this set to 5000 mm/sec possibly.

 

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Hi,

thanks for the advice again! I've done a few other prints of which two succeeded and one fail due to this problem. I checked the belts again and also checked all screws. I must admit I missed one screw the first time! It was the screw in the pulley on the short belt of the X-axis which is a seperate pulley. The Y-axis pulley is a one-piece pulley so there's a difference which I didn't notice the first time. My bad... :oops: . It's tightened now.

I also noticed some black 'sparks' on the bottom of the machine behind the cover. These seem to come from my belt since there were also a few on the motor itself. I moved the motor's pulley as far towards the motor as possible without it touching the motor.

Furthermore the X-axis runs as free as the Y-axis when moved by hand.

Tomorrow attempt nr. 3-4 to solve this nasty problem.

PS: Where can I set the XY acceleration? :oops: Is that in Cura?

 

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Where can I set the XY acceleration?

 

On the front of the printer. I haven't played with it:

maintenance/advanced/motion settings

I suspect if you turn the machine off and on again it will go back to defaults unless you choose "save" or something. That's how it works on the UM1 anyway.

 

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I also noticed some black 'sparks' on the bottom of the machine behind the cover. These seem to come from my belt since there were also a few on the motor itself.

 

This is 95% chance the problem. I'm certain this was it. I would clean out the specs and if they are still there later then something is still rubbing.

 

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I think they really need to learn how to tighten screws properly. On my new UM2 i also had to tighten all the screws because my prints were screwed up. First time i forgot my extruder screw. that cost me another ruined print...

 

The easiest thing to "learn" how to tighten screws properly is to use a torque screwdriver. It's also the fastest way to work because you don't have to worry about getting the torque right anymore but you can just screw on until it slips.

While we're at it, use only Swiss quality tools of course:

http://www.pbswisstools.com/en/quality-hand-tools-qht/screwdrivers/torque-tools/mecatorque.html

By the way, these are not even expensive, they're actually among the cheapest torque tools I've seen so far, but it works like a charm and has a great grip.

Considering the UM vibrates quite a lot when printing fast, it could also make sense to use a threadlocker like Loctite 243 (metal screws AND threads only! Standard threadlockers don't take plastic well) for some screws. This is also common for example with RC helicopters to prevent screws from coming loose because of continuous vibration.

/edit:

Almost forgot: Of course you need to know what torque is optimal, but once someone determined that and wrote it down, it's easy to reproduce with a torque screwdriver. You can just "determine" that by hand if you're experienced enough, that's not rocket science...

/one more edit:

By the way, the MecaTorque is newer (2013) and better than the DigiTorque, even if it seems to be the more out-of-fashion way of making a tool.

 

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This problem is now solved. The screws needed to be tightened and the pulley was rubbing the short belt. Two fails of the Ultimaker's assembly team in my opinion but I'm very happy it's working now!

I've made some very nice prints so far but now my nozzle seems blocked...

 

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