a5:layer-shifting

Layer Shifting

Layer shifting is a problem occurring with some A5 and A3S printers. While there are several root causes, this printing defect occurs whenever the printing head, or printing bed, are shifted, without the controller being aware. The printing process is an open-loop control system, so there is no way for the controller to know that something has gone wrong.

Under normal operation during printing, the stepper motors maintain control of the x, y and z axis position at all times. The stepper motor generally has sufficient power to overcome any minor resistance forces like friction and inertia, and if you push lightly on the printing head or bed while printing, the printer should be able to resist your forces.

However, if a force is applied that exceeds the grip strength of the motor, the motor's control will be overcome. When this happens, a layer shift may occur.

There are several possible causes for a layer shift:

Poorly tuned Stepper Drivers

Out of the box, some A5 and A3S printers have been delivered with untuned stepper drivers. The stepper drivers are the chips that are responsible for powering each of the motors. These stepper drivers have a small adjustable potentiometer that sets how much current is delivered to each motor. Too much current, and the stepper driver may overheat โ€“ when this happens the driver may briefly turn off to enable it to cool down, and this may result in a layer shift. Too little current, and the small resistance forces that occur during printing may overcome the motor, and a layer shift may occur. For more information on how to properly tune your drivers, see this page.

Overheating Stepper Drivers

Especially if you've upgraded your steppers to TMC2100 or TMC2130 you will need cooling. But even if you haven't its possible that with complex prints, lots of movement the drivers get overheated. When this happens they stop processing (for a short while) with a layer shift as result. For this reason its advisable to add cooling. This can be as simple as putting small fans behind the drivers upto fanducts which you can find on thingiverse.

Loose Pulley Grub Screws

The motor shafts transmit power to the timing belts through toothed gears, known as pulleys. These pulleys are fixed onto the motor shaft by a very small screw, known as a grub screw. If the grub screw is not tightened, this may cause the pulley to slip on the motor shaft. This can cause a layer shift.

Loose Belts

If the belts on the A5 are not tightened sufficiently, they may be able to slip on the pulley. This can cause a layer shift. The belts on the printer should be able to be plucked like a string, and you should hear a mid/low pitched note. Tightening the belts on the A5 is not easy. The best suggestion has been a four step process:

  1. Work out how much the belt needs to be tightened
  2. Slide the belt off one of the motor pulleys
  3. Adjust the belt accordingly while it is loose
  4. Slide the belt back over the motor pulley again

Loose motor cable plugs

If any of the plugs and connectors that link your motor to the motherboard are not fully inserted, this can cause a bad connection with erratic results. Check that all your plugs are fully and firmly inserted.

Bad Bearings

The bearings on the A5 are not high quality. The y-axis bearings may become stuck from time to time, and this can cause a layer shift. Replacing a bearing on the A5 is a long process, and there is no video or documentation for this process yet. Several members have replaced the ball bearings with IGUS linear bushings. Another good alternative for replacing the ball bearings are brass bushings with graphite lubricant.

It is also important to regularly wipe down the linear rails to remove any debris, and also to periodically lubricate them if you are using ball bearings. The correct lubricants are discussed on the maintenance page.

Printing too fast!

If your printing settings are too fast, you may exceed the ability of the motors to maintain the position accurately. This can happen by having set the printing max speed too high, or using acceleration or jerk settings that are too aggressive. An example on the A5 is the y-axis - the weight of the printing bed is high, so the maximum possible safe speed is lower than for the x-axis.

In cura you can set these under the tab 'print speed':

  • go through all the speed settings and limit those to max 80 mm/s
  • enable acceleration control, this is by default 3000 while the firmware has a limit set of 300 (which is a cause for the difference in actual and estimated time). You can lower this e.g. to 200 for ALL accelerations
  • enable jerk control, this is by default set to 20mm/s, you can lower this to 10mm/s or even 5 if you still have issues.

Nozzle hits the printed object

Its possible when the nozzle temperature is too low that the nozzle starts hitting the print when it gets > 10cm (approximately). This is easily detectable as you can clearly hear this. This can lead to a print being knocked over, it can also lead to a layer shift. The easy remedy is higher temp. In my personal completely biased experience: small complex models I print at 190C (less stringing) while higher less complex models I print at 210C to prevent crashing (at the price of stringing).

Axis rails not parallel

A very rare, but still real possibility that has occured before: check that the rails on your troublesome axis are parallel. If the rails are not parallel, then there will be an increase in friction as the carriage slides along the axis. Even a small deviation of less than 0.1mm can cause issues! If you find that friction changes along the length of an axis, of that it gets stuck in one part of the axis, then check that the guiding rails are completely parallel.

a5/layer-shifting.txt ยท Last modified: 2019/07/25 03:23 by samuelpinches