In this post, we will discuss a group of issues related to printers operating with FDM (Fused Deposition Modeling) technology: more precisely, the impact of the Jerk parameter on our printer and on our prints.
Most probably you have happened to print a model that seemed to be perfect (seen in a slicer or in a modeling software) and have noticed, then, in printing, some defects.
First of all, therefore, it is necessary to establish if your problem may or may not belong to the category of problems that we will try to understand and solve in this article. In the following image is shown the comparison between a model that has no defects (lighter model on the left) and one that has some defects (darker model on the right).
Look at the letter X and note how, on one side of the letter, it is possible to notice signs comparable to “an echo”. One of the sides of the model also has the same defect.
Then compare the edges of the squared part of the two models. You will notice that the edges are presented differently in the two models.
Defining the mechanical problem could be difficult. If, for example, we were to drive our car at night, in total darkness, with a single headlamp, we could do so, but perhaps it would be better to decrease the speed. That is, even if the car is not in optimal condition, you can still drive it. But you cannot drive it the way you could if both lights were working. A compromise is therefore made.
Mechanically it would be appropriate to check (the mechanics of the printer must always be in order, otherwise, solve this type of problem common to printers, it could be impossible):
- Tension and belt state (the belt must not be elastic, must not be too tight, nor too loose)
- Mechanical games (bearings, bushings, screws, nuts, guides, worn parts in general)
- State of the frame and of the printer in general (tension and possible play of the screws)
Theoretically, the printer head (i.e., the axis where the nozzle is mounted) should work like this:
But you could do something like this. The head is over the final point of arrival due to a mechanical problem. Here the problem is exaggerated, but it shows the effect well:
In this case the slicer software does not seem to be directly responsible for the problem. Instead, it can be “configured” to mitigate or even solve the problem.
When the head starts to move, it does not move immediately at the “final” speed. For example, if a model were to be printed at 60mm per second ( 60mm/Sec ), its printing would start at a point, decided by the model and the slicer, and would move to a new point accelerating at the beginning and then decelerating as the end point approaches.
If it wasn’t so, the whole structure of the printer would be affected, so much so that it could be seen, in some way, swinging.
If we used the car once again to make an example and if, for example, starting from a standstill, we had to make a sudden start, we would be pressed against the seat, or if we had to brake abruptly we could even be thrown out of the car!
This means that instantaneous changes of speed, and above all, towards different directions, are not allowed (or almost).
In this case, the right solution to solve the problem seems to be to set a value for the Jerk parameter lower than the one set by default.
That said, the only efficient way to solve the problem, is to do some test prints, changing the parameter a little at a time (step of +10 -10, a common value is 20) and compare the results each time. The image model has been specially created for this purpose. You can find it HERE.
If the Jerk parameter is too low it is likely that the sharp edges will be rounded and/or show other defects. If too high, it may create “dangerous” oscillations. However, keep in mind that the goal is to get a cube that looks as similar as possible to the lighter one.
Note: The parameter Jerk or tear is a definition in physics, but in the case of 3D printers is used to indicate ( since it is the firmware to manage the behavior of the printer ) the maximum value of the instantaneous change of speed.
How to change the Jerk parameter
- From the printer controller. It is possible that your printer offers, among the menu items, the possibility to modify this parameter. ( It is not necessary to save the new value in the EPROM memory. However, if you do not and if you follow this method, after each power on of the printer you will be forced to reset it)
- Using the Gcode instructions. If your slicer offers the possibility to add Gcode instructions at the beginning of printing, then you can add the M205 command. Different firmware, different command options. HERE you will find the complete description of the command and its compatibility with your firmware.
- Changing the firmware. It is the longest and most complicated procedure. Not everyone knows how to download, configure, compile, transfer a firmware to their printer, and in fact, it’s not exactly an everyday thing. Moreover, this could only be possible on non-professional printers, where changing the firmware could instantly void the warranty. Using different procedures that vary from firmware to firmware and from printer to printer.