Unexpected y-axis shift mid print

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rrocket
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Unexpected y-axis shift mid print

Post by rrocket » Mon Jun 22, 2015 11:45 pm

I am printing a long part (~240mm in the y-direction) and twice now I have printed this part there is a sudden shift in y-axis. In the first case, the printer is printing off the table after successfully putting down about 20 layers. I stopped the print and exited Simplify 3D and reloaded the part and started again. On the second print, the printer does the same thing. The part is/was securely fused to the table during the print and there is no part-shift. On the first print the shift was about one inch in the + y-axis. On the second part the shift was in the - y-axis by a much smaller amount perhaps a millimeter or so but still noticeable and problematic.

Can you suggest a solution here?

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Jules
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Re: Unexpected y-axis shift mid print

Post by Jules » Tue Jun 23, 2015 12:27 am

Rotate the print so that it lies on the diagonal.

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jimc
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Re: Unexpected y-axis shift mid print

Post by jimc » Tue Jun 23, 2015 12:57 am

wow 1" is alot. ok here is a list of most of the more common causes of shifting.

1: overextrusion
2: warping of the print
3: accelleration too high (default is 3000) lower to around 1000
4: x/y movement speed too high. s3d default is 18000. lower to 9000-12000.
5: loose motor pulley set screw
6: loose belt
7: no oil on rails or threaded z axis rod
8: bad wire harness
9: model is bad and has errors causing slicing error

Vandal968
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Re: Unexpected y-axis shift mid print

Post by Vandal968 » Fri Aug 28, 2015 6:09 pm

I know that this is an old-thread, but....

I've experienced the Y-axis shift, but only on large parts. It appears to be weight-related. IE: the stepper has more and more trouble accelerating the Y-axis as the amount of material on the bed increases. At the default speeds:

X/Y Axis Movement Speed 18000mm/min
M201 X3000 Y3000
M202 X3000 Y3000
M204 S3000

I can print parts up to about 45gr before I get my first layer shift. As the part grows the shift become worse until I've got a mess. This is consistent across different parts. It appears that the stepper is unable to accelerate a (relatively) heavy load rapidly enough and loses steps. The Y-motor would typically make a burp noise when this shift happened, although now that I'm running the motors on isolators, you can't hear the shift even though it still happens.

Here is a part printed with the default values, notice the first shift near the base and that the shift rapidly grow worse as the weight of the part increases. First failure at about 40grs (as estimated by S3D):
Image

Changing the values to the following:
X/Y Axis Movement Speed 18000mm/min
M201 X2000 Y2000
M202 X2000 Y2000
M204 S2000

I was able to print this Terminator skull up to layer 91 before the first shift, more shifts started happening frequently beyond that point. The failure point is at the cheekbone/bridge of the nose (155gr). I cancelled the print and printed just the top seperately (144gr) and glued them together, but you can see the repair. With the lower acceleration values, I was able to print more than 3x the amount of plastic without issue compared to the default values.

Image

Belts are snug, as are setscrews. I have marked witness lines on motor shafts, pulleys and belts, no mechanical shifting has taken place. The motor is definitely losing a step and reducing acceleration vastly improves it. The question is how low does it have to go to eliminate all shifting while giving-up the minimum amount of speed, and also, can the current to the motors be increased to help prevent this issue without having to slow the printer. Another option would be to alter the acceleration values in the gcode as the part gets larger. That way you'd have max speed for little parts and maximum safe speeds for successful printing as the parts grows. Observations/comments welcomed. Cheers, c

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ednisley
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Re: Unexpected y-axis shift mid print

Post by ednisley » Fri Aug 28, 2015 10:39 pm

Vandal968 wrote:parts up to about 45gr
The platform weighs about a kilogram, so a few additional grams of plastic won't have much effect on the force required to accelerate the Y stage.

Looking at those failed objects suggests the nozzle whacks against a curled-up bit of plastic and stalls (in one axis) until the next G-Code command. That commonly happens with multiple objects, objects with multiple small projections, or large objects with complex interior features: acute perimeter angles tend to curl upward as the hot plastic on the sides cools and contracts.

Aggressive cooling can sometimes reduce the curling by quickly solidifying the plastic, but the Big Hammer seems to be using "Retraction Vertical Lift" (in S3D) or "Lift Z" (in Slic3r) to raise the nozzle (by lowering the platform) after each retraction, so the nozzle has enough clearance to miss even the worst curl.

If you set retraction to happen only before perimeter crossings, the platform won't do too much hopping...

Vandal968
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Re: Unexpected y-axis shift mid print

Post by Vandal968 » Fri Aug 28, 2015 11:25 pm

I've had no curl whatsoever on these parts that I'm using as examples, they were flawless right until they shifted. On prints where I have had curl or blobs even when the nozzle was loudly dragging, I still never ran into a shifting issue until I hit 40-45gr part weight at the original settings or ~150gr at the reduced (2k) settings. Originally, I thought that the the length of the print might be an issue from a heating standpoint since I only saw the issue with long prints (maybe the drivers were hitting a thermal cutoff). I added heatsinks to the drivers & cpu which substantially lowered their operating temperatures, but had no effect on this issue. If it is weight/acceleration related, which I strongly believe it is at this point, I should be able to just clamp some weights to the table and reproduce the issue with a fairly small part and a weighted table. I will experiment with retract, but these prints I'm showing were all running very smoothly and the nozzle was not hanging-up on anything.

What values are you running for:
-X/Y Axis Movement Speed
-M201
-M202
-M204

What's the biggest thing that you've printed without a shift?

cheers,
c

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jimc
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Re: Unexpected y-axis shift mid print

Post by jimc » Sat Aug 29, 2015 3:08 am

this has nothing to do with weight. many of us are running 1/4" thick aluminum build plates that weigh 2 pounds. you can't run 18000 xy movement speed. drop that down to 9000-12000 and the acceleration values that are 3000 default, drop to 1000. you will have cleaner prints and no skipping. with all that said there has been some recent discovery that the skipping is due to the arduino compiler version. in any case dropping those values down will stop it unless its actually nozzle hitting, belt or pully slippage.

Kulturfolger
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Re: Unexpected y-axis shift mid print

Post by Kulturfolger » Sat Aug 29, 2015 8:40 am

Thats a glitch in the firmware: viewtopic.php?f=10&t=2568&hilit=firmware+travel

Reinstall your firmware with the OLD IDE! http://makergear.wikidot.com/m2-firmware
Feel free to correct my mistakes. English is not my native language.

Vandal968
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Re: Unexpected y-axis shift mid print

Post by Vandal968 » Sat Aug 29, 2015 11:14 pm

I'm running Marlin 1.0.2 installed from the 1.5.5 IDE

Cheers, c

Kulturfolger
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Re: Unexpected y-axis shift mid print

Post by Kulturfolger » Sat Aug 29, 2015 11:31 pm

Yes, same here: While printing something something complex these shifts happen. What I did is lower accel and jerk. When I double the default values this effect vanishes but the artefacts are unaceptable.
Feel free to correct my mistakes. English is not my native language.

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