What could be causing my y axis to slip?
Occasionally, while printing, my y axis will slip and the layer will, from that point forward, be shifted, ruining the print.
What might be the causes of an axis slipping? I have tried cooling the motor which seemed to have been getting warm, and the belts are not too tight.
This does not happen with every print, and seems to be an intermittent problem.
My printer is a MendelMax RepRap, and the y axis is my moving bed.
The belts being not too tight can be the problem. If I don't tighten my belts, the belt slips off the motor. What sounds does it make when it skips? Also, how much force does the bed require to move?
I know it's an answer to a somewhat different question than you've asked, but one thing you can do to mitigate axis slippage until you can figure out what's causing it is to home the X and Y axes between each layer. This will guarantee that if you slip during one layer, only that layer is off, and the next layer will be lined up correctly again.
FYI, the way stepper motors work is they are always "on", so being pretty warm when even not rotating is normal. That said they can skip steps if too hot, so adding a 4cm heatsink+fan is worth it and isn't hard or expensive.
Hello @Matt Clark, I noticed your question has been up for a while now. Have any of the answers below been able to solve your question? If so, would you mind accepting the appropriate answer. If not, what is missing so that we may help you further? Also, if you have figured it out on your own, you can always answer and accept your own solution. Thank you.
@MattClark, when you post a question like this one, it is very helpful if you can include photographs of the result. I was confused (nothing new) by the photo in one of the answers, and wrote an answer addressing the particular problems it demonstrates, only to realize during my review that it wasn't your problem! Pictures help people help you. If you have found the cause, please accept the best answer. It we didn't identify it, you might write and accept your own answer. Our goal is to have a record of great questions and spot-on answers to help the next person.
Your printer is skipping steps in the y-direction. This can have several causes. Take a look into Shifted layer guide on RapRap.org which lists 29 possible problems that can cause this issue and how to fix them.
First items of the list:
- Driver current is too low
- Driver current is too high
- Belt too Loose
- Belt too Tight
- Loose Set Screw/Grub Screw
- Belt or Bearing is binding
- Speeds are too high
- Acceleration is too high
When I was dealing with this issue on my RepRap I had to increase current to the particular driver.
Something else that I have also run into that can cause skipping is the filament not spooling smoothly.
worn out/low quality linear bearings and rods they slide on can contribute to 4, 7 and 8.
I had the same problem on my Mendel, and it turned out that speed and acceleration were too high. But as @amra said, there are a lot of thiings that can cause this problem.
In my experience, the most common reason for positional offset during printing, is the motor skipping steps due to physical impact.
Your stepper motors do not give positional feedback to your printer. So, if you forcefully move your motor during print, then the printer will not notice, and simply pretend it never happened.
In particular, the motor could skip steps if:
- Your nozzle collides with erroneous extrusions (e.g. blobs) during print.
- Your speed settings (jerk and acceleration) are too high for the mass (inertia) of the parts moved by the y-axis motor.
Smaller collisions and nozzle drag at high speed (e.g. during travel) could also cause this problem, since the strength of stepper motors is reduced at high speeds.
+1 for the note about no positional feedback. This is so frustrating, you spend sometimes thousands of dollars on a machine that doesn't know where it is.
@tbm0115 that is very true indeed! I am hoping for that to change as the treaty printing technology matures!
I thought I heard somewhere that the NEMA motors have a way to know which step they're on, but the controllers only interact with the motors in increments. There might be a way to at least create some form of "endstop" that recognizes the stepper is out of sync and "pauses/stops" the machine.
I believe most stepper motors only have an *open loop* control, which means that they don't know their own position. However, a *closed loop* control (with positional feedback) is usually not needed, since they have excellent precision and torque as long as the motor is properly scaled for their application. Also, for some applications - unlike in 3D printing - skipping steps doesn't really matter. You could, add an *encoder* to the shaft for providing positional feedback. And just like you say, some steppers also come with such encoders integrated.
@tbm0115 Some stepper drivers can detect skipped steps by sensing variations in the current going to the motor. However, NEMA motors don't have a way to "know" what step they're on. There are no electronics inside, just some coils and magnets.
The current to your motor driver could be set either too high or too low. If it's set too low then the torque might not be sufficient and the motor will skip steps. If it's set too high then the driver might overheat and occasionally shut down to protect itself.
Another option is that the printing speeds (or jerk/acceleration settings) are too high. I would start by reducing the travel speed (which presumably is higher than your printing speed) and see if that makes a difference.
The motor getting warm is normal and will not cause these issues.
From what I've experienced, there could be three potential reasons.
- Your belt(s) could be loose. Simply loosen your Y-Axis motor and pull the motor until the belt is slightly more than taught (it will relax into a taught position). Then, tighten the motor securely in its place.
- One of your axis endstops could be triggered mid-print. If you have a larger print, you run the risk of hitting an endstop, which could cause the machine to lose its coordinate system.
- I found on my machine, if you run your program via USB (on MakerWare specifically, possibly others) there might be some sort of lag in the serial connection that could cause the entire program or coordinate system to shift. I repeated this issue multiple time using a USB connection and fixed it (repeatedly) by either running off of an SD card, using a different slicer (in my case the Cura plugin for OctoPi), or trying an earlier version of your software (this was my long term solution).
The latter worked best for me. I tried running MakerBot Desktop on my Dual Replicator 1, but ran into the same exact issue as you. In fact, I encountered this issue around firmware 5.0 on the Replicator as well (7.? is the latest). Finally I switched back to using MakerWare 2.4.? and everything worked fine.
I had a repeatable problem where my prints were shifting to the side after about 5mm. This was down to a loose z-axis guide rail that would come out of it's end support about 5mm into the print but appeared secure when the bed was set to it's initial position (my print head moves down). There was a grub screw hidden below a panel at the base of my printer, I'm not familiar with the build of the MendelMax so this may be different for you.
Given the last few questions you have.. I am going to say that you have too much mass.
F = M*A. If you are trying to move a heavy plate, you will need to reduce the Jerk setting. As well as maximum acceleration.
Post your firmware settings for more advice.
Also just for completion, sometimes the pololuls overheat. that can cause it too. As well as a loose belt.
I have some suggestions that might solve your problem
Try to use belt tensioner which is suitable from your printer.(You'll probably find one on Thingiverse)
The belt has teeth but your bearing which slides your belt does not. So try a bearing cover that has teeth. That will prevent slipping of the belt.
Most importantly lower your acceleration constant. This has a lot to do with missing steps from the motor.
Decreasing the print speed can help as well.