Sunday, February 12, 2023

Tips and Tricks For Printing Small Gears

It is sometimes difficult to print small gears. Typical problems are teeth pulling up or distorting or simply the whole thing coming loose and sticking to the nozzle. I don't believe there is any universal solution to this, so here are a few tactical things you can do. Obviously start by making sure that your printer is well calibrated, the print surface and nozzle are clean, and that the bed is levelled. I usually clean the nozzle by heating it to just under the print temperature then removing any stuck on filament by lightly brushing it with a brass wire brush. It helps to put a mirror on the print bed so you can see what you are doing. I have a concave shaving mirror that also magnifies. My Prusa MK3S is set up for levelling using a slight modification together with an associated process known as "bed levelling without wave springs" (it's a misleading name reflecting the history of how the author of the process got there), and if you put in the time with this you can get a very accurately levelled bed.

The problem with small gears is that you can get small segments in the teeth which result in a lot of nozzle moves and retractions. Due to the viscosity of the filament, the move may pull the feature it has just printed off the print surface or plow through a small feature which is isolated from other features and so doesn't have much attachment area. Generally once you are past the first layer, things will go OK. You might get some stringing or blobs, but you can fix these up when the print is complete.

A first thing you can do is examine the features in the slicer preview and adjust settings to try to avoid such features. For example if you see something like the small triangles and dots in this example, you may be in for a problem:

There are several parameter changes which may help. It's not possible to say that any of them will definitely improve the slicing. The best thing is try them, look at the result and see if it appears better:
  • increase or decrease the number of perimeters. Stick to a minimum of 2. More perimeters give you greater strength and rigidity. If the gear doesn't take much load (for example, the gear train from minutes to hours) then 2 will be strong enough.
  • reduce or turn off elephant's foot compensation. It makes the first layer smaller, so making it more prone to these small features. If your printer is well-calibrated, you may not need it anyway.
  • switch between the Arachne and classic slicing algorithms. Sometimes one just does better than the other.
If you have access to the model you might also be able to tweak it, but that's a bigger task and doesn't always help.

Another setting that can be useful is external perimeters first. This won't change the slicing, but guarantees that you have a single solid outline for the remaining tracks to stick to.

No comments: