Random Y-Axis Shift

My problem is: I will be printing and everything will be going perfect, all the layers are stacked precisely on top of one another, then every once in awhile, there will be a shift on the Y-axis of a few mm, and the next row will be offset by a few mm, then it will return to stacking perfectly, but offset. So, I'm printing stuff that looks like it's been chopped in half then glued back together offset. My jerk limit is 10mm/s, acceleration is 1000mm/s2, and my print speeds are well within safe limits -- 40mm/s -- so that the print won't get messed up by the jerk of the machine. All limit switches are disabled during printing, so I'm sure it's not them. The motor is strong and has the proper amount of power to it.

My friend is having this same problem too, we both have ORD Bot Hadrons with Ramps 1.4. He just replaced his Arduino Mega 2560 to see if that would solve it, because nothing else worked, and we have yet to see whether that will solve the problem.

Attached is a picture from google images that looks like the problem I'm having

Edited 1 time(s). Last edit at 02/03/2015 03:46PM by kre8.

It seems like someone else on here solved a similar problem by changing firmware, but I'd rather not do something so severe. I just discovered that I can hit the home Y axis button in repetier mid-print, and it will home the axis after it's done the layer that it's working on. Certainly not a fix, but it might save a print or two.

Edited 1 time(s). Last edit at 02/03/2015 04:22PM by kre8.

It's a case of either printing too fast, having too low power to your stepper motor, or having a belt skipping.

The Y-axis is usually heavier than the X-axis, this is why this happens to a lot of people that just started printing with their new printers. The printbed just has more mass and most of the time this is the problem.

You can try:
- Printing slower, with less acceleration
- Upping the power on the driver of the Y-axis (don't go too high)
- Tightening your belt if it's too loose

Changing firmware will not improve this problem. Unless it has different (slower) acceleration settings of course

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http://www.marinusdebeer.nl/

This is a very common problem.

This us usually caused by a thermal reset in one of your stepper drivers. They get too hot and shut themselves down for a short period (and that period varies!).

I had this problem for some time, and thought it was too much acceleration. It wasn't. I discovered this when I tried a Smoothieboard (which is awesome) instead of a Rumba, at low accelerations, and the problem persisted.

Then I put a very powerful fan blowing on the drivers and that solved the problem completely. Note that I am running at a higher than normal voltage, so a bit more heat is generated.

So to fix this you have some choices:
1) You can turn down the current going to the motor(s). Since you know which way it shifts you can tell which driver needs to be turned down, just a bit. You can also feel the drivers (carefully!) and if one is going to burn you, that's the one! Turning down the current too much will cause loss of torque - and lost steps also.
2) Put a powerful fan or blower, and heat sinks on the drivers, and even duct the air so it is more effective. I printed a special ducted enclosure for my smoothie that cools both sides of the drivers... no problems now - with a lower fan speed.


Other things that can cause it are: too much acceleration (much less likely), loose belts, slipping pulley (grind a flat on the stepper shaft), too low current, or something binding.

Hope that helps.

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My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
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Reduce the acceleration to 500mm/s2 and adjust the stepper current. With the printer idle but the motors powered for a few minutes, feel how warm the Y motor and Y stepper driver are. If both are cold, increase the current. If the driver is hot, reduce it or add a cooling fan (see the previous reply for the explanation in this case).

Edited 1 time(s). Last edit at 02/04/2015 04:12AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I think I solved the problem in a different way than these good suggestions. In the firmware I changed ALWAYS_CHECK_ENDSTOPS to false. Before I was shorting out all the limit switch pins with short wires so that I wouldn't get any false readings, but perhaps that wasn't quite enough. In any case, I've been printing nearly flawlessly for 24h now.

The heatsinks on the drivers are pretty warm, but not too hot to hold my finger on. I'll keep my eye on them, I never thought of checking them, that's a good suggestion to make sure they're cool.

Edited 2 time(s). Last edit at 02/05/2015 12:56PM by kre8.

Still getting small Y shifts, 0.5~2mm. They're quite infrequent and often don't ruin the print, especially if I notice it soon after it happens and re-home the axis. It's still only happening on the Y axis. I find it very unlikely that it's driver heat, as I now have a surplus of fans surrounding the board in response to the suggestion that driver heat might be the problem. The axis homing is disabled in the firmware, so it's not limit switches. The Y motor gets as warm as skin, certainly not too hot. Belts and screws are all tightened and are no other significant printing problems. I'm printing large, complex objects with very good performance aside from this Y-shift issue.

1. Check that the pulley is secure on the Y motor spindle.

2. Reduce the Y acceleration. 1000mm/sec may be too high, depending on how heavy the Y bed is and the steps/mm in your setup. And the bed gets heavier as your print builds up.

3. Keep an eye out for the head snagging on the print.

Edited 2 time(s). Last edit at 02/07/2015 01:23PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Ok, I'll try reducing accelleration, that sounds promising. My bed is pretty heavy.

Edited 1 time(s). Last edit at 02/07/2015 01:29PM by kre8.

Had a very similar issue it seems silly and obvious after the fact but try some 3:1 oil on your smooth rods, I did and mine stopped the issue immediately

Update: everything has been going good for a full week of nonstop printing. I replaced the belt clamps with ones that had teeth, printed some smaller pulleys so that the belts are more parallel (the pulleys I had were definitely too big), and lowered the x and y accel. to 500mm/s2. With the new clamps and pulleys I'm able to keep the belt much much tighter than I was before, and the accel. might be playing a role too. I'm printing at 180mm/s flawlessly. With the low acceleration 180mm/s isn't even much of a problem, as If there's a long straight line it'll get going that fast, but for very small movements it doesn't go crazy and start shaking the whole frame: it's very gentle speed.

Now to get some 80 degree overhangs working!