It is not a calibration problem. PLA and other thermoplastics shrink while they cool so you will always get parts that are slightly smaller than the model.
Thanks for your reply.
It does seem to me, given that the firmware knows I am printing in PLA since I selected that in the menu, I should also be able to tell the printer that "this particular brand of PLA shrinks by 0.6% after printing". Or if all brands of PLA shrink about that amount, then the printer firmware should already compensate for it. Is there a reason why the printer should pretend that PLA doesn't shrink at all? Is there a problem with having a firmware calibration constant for this? If there was such a factor, I could print the same .gcode file in either PLA or ABS (after selecting the material in the printer menu of course) and have them both dimensionally correct.
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anon4321 16
It is not a calibration problem. PLA and other thermoplastics shrink while they cool so you will always get parts that are slightly smaller than the model.
There are three solutions to this listed below in most recommended to least recommended order -
Most - Use Cura to scale the model before printing by a small percent.
Medium - Use a CAD program to design or alter a model to account for shrinkage
Not recommended - Change the steps per unit in the firmware.
UM has calculated the correct steps per unit based on the mechanisms (pulleys) used. When the firmware needs to move the head a distance of say 10mm, the steps per unit are calculated such that the head accurately moves 10mm. It's not recommended you change these values as the error comes from another issue namely the shrinkage.
The next one, changing the model, means that the model becomes specific to the type of material. If a model is altered to account for the shrinkage of PLA then it won't be accurate when it is printed in ABS which has a different shrinkage factor.
The Z axis error is probably do to the bed leveling/distance to the nozzle which is very hard to get accurate.
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