Object Height Incorrect
Posted by mancinism
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Object Height Incorrect February 28, 2014 09:31AM |
Registered: 10 years ago Posts: 15 |
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Re: Object Height Incorrect February 28, 2014 11:12AM |
Registered: 10 years ago Posts: 2,472 |
First make sure that the design file is indeed the height that you believe it to be in case the problem is with your STL export. You could load the STL into NetFab (or any other STL viewer) and see what height it reports. Also ensure that you don't have any scaling factor set in Slic3r (Slic3r is capable of scaling your STL).
The amount that the Z axis lifts for each layer is determined by the amount commanded in the G file and the number of steps per mm set up in the firmware - which is a fixed number because it is determined by the mechanics of the Ormerod though it can be over-ridden by an M92 command, so make sure that there is no "M92 Zxxx" command in your config,g file or in the start or end G codes set in Slic3r - the only M92 command you should ever see is the one that sets the extruder steps per mm in config.g ("M92 Exxx"). One complete revolution of the Z stepper motor lifts the extruder by exactly 1 thread of the leadscrew which is the same for every machine and is precise, so it does not require calibration. It is extremely unlikely that Slic3r is sending incorrect commands or incorrectly computing the number of layers, and the value for the number of steps per mm is correct in the firmware, so we need to look elsewhere for the cause of your short prints.
The most likely cause in my opinion is that the Z stepper motor occasionally misses steps, probably due to too much loading - perhaps the gears are sticking or the leadscrew is binding on the nut. Try turning it by hand with the machine off and see whether it feels stiff or you encounter stiff spots as you turn the leadscrew. You can try turning the stepper current up in config.g("M906" command line) - I set all my motors to 1000mA instead of the default 800mA.
You can see whether the Z axis works OK in isolation by homing the Z axis as you usually do, and then commanding the Ormerod to raise it by a large fixed amount by sending say, "G1 Z150" which should raise the nozzle to exactly 150mm above the bed, which you can measure. If it does not raise it high enough, do it again and watch and listen as you raise the extruder - it is likely that you will be able to see/hear the reason for the missed steps.
If that test shows the extruder lifting to exactly the correct height, then the missed steps are probably occuring in the many Z movements that occur on each layer due to the bed compensation. It could be that this is causing the Z axis to move too fast because your bed is too far from being level - you should mechanically level your bed so that the difference between highest and lowest spot is within a mm, or 2 at most.
If none of that helps post again and other brains might figure out what is going wrong.
Dave
(#106)
The amount that the Z axis lifts for each layer is determined by the amount commanded in the G file and the number of steps per mm set up in the firmware - which is a fixed number because it is determined by the mechanics of the Ormerod though it can be over-ridden by an M92 command, so make sure that there is no "M92 Zxxx" command in your config,g file or in the start or end G codes set in Slic3r - the only M92 command you should ever see is the one that sets the extruder steps per mm in config.g ("M92 Exxx"). One complete revolution of the Z stepper motor lifts the extruder by exactly 1 thread of the leadscrew which is the same for every machine and is precise, so it does not require calibration. It is extremely unlikely that Slic3r is sending incorrect commands or incorrectly computing the number of layers, and the value for the number of steps per mm is correct in the firmware, so we need to look elsewhere for the cause of your short prints.
The most likely cause in my opinion is that the Z stepper motor occasionally misses steps, probably due to too much loading - perhaps the gears are sticking or the leadscrew is binding on the nut. Try turning it by hand with the machine off and see whether it feels stiff or you encounter stiff spots as you turn the leadscrew. You can try turning the stepper current up in config.g("M906" command line) - I set all my motors to 1000mA instead of the default 800mA.
You can see whether the Z axis works OK in isolation by homing the Z axis as you usually do, and then commanding the Ormerod to raise it by a large fixed amount by sending say, "G1 Z150" which should raise the nozzle to exactly 150mm above the bed, which you can measure. If it does not raise it high enough, do it again and watch and listen as you raise the extruder - it is likely that you will be able to see/hear the reason for the missed steps.
If that test shows the extruder lifting to exactly the correct height, then the missed steps are probably occuring in the many Z movements that occur on each layer due to the bed compensation. It could be that this is causing the Z axis to move too fast because your bed is too far from being level - you should mechanically level your bed so that the difference between highest and lowest spot is within a mm, or 2 at most.
If none of that helps post again and other brains might figure out what is going wrong.
Dave
(#106)
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Re: Object Height Incorrect February 28, 2014 01:07PM |
Registered: 10 years ago Posts: 14,672 |
I had the same problem for a while when the z-gears were too stiff, causing the motor to miss steps occasionally.
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].
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].
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