I have been designing 3D-printed items for some years now, first in blender and later in CAD. I don’t necessarily make the most complex designs, but I have specialized a bit in items that are very easy to print for anyone. Here’s a few things I learned, maybe you can take some away from this for your own designs.
General approach
You want to think like your slicer. Before you even draw the first line in your software, think your object though and consider how the layers will stack. Make some pencil drawings to help you conceptualize it. The goal is as few supported areas as possible, ideally none.
Do not start designing with the idea that you can just figure out how to print it when you’re done. Printability should be in your mind every step of the way.
Consider the line width
You most often will be printing with an 0.4mm nozzle, so that will be the line width. In your slicer you may be seeing a slightly larger line width, but that is so the lines have a very small overlap and make good bonds with each other; when designing things you should think of your line width as the nozzle diameter.
So when you’re designing for example a box, the best practice is to make the wall strengths of that box a multiple of your line width. 0.8mm for 2 lines, 1.2mm for 3 lines, 1.6mm for 4 lines and so on. This way you will be printing only with well-bonding, fully extruded lines.
Your slicer will most likely be able to do Arachne wall generation. This allows your printer to fill in gaps with under-extruded thinner lines, but If you can design your objects so you don’t need this, I recommend doing so and staying with Classic.
Overhang angles
The angle of overhang you can cleanly print mostly depends on the filament you use. A dialed-in PLA can fairly cleanly print overhangs of 60-ish degrees, while for example PETG which needs to be printed with the cooling fan turned down or off will most likely make a mess at that angle. I recommend keeping your overhangs at or below 45 degrees. That angle works flawlessly with every filament I ever printed.
Beware of fillets! It’s tempting to create fillets instead of a chamfers for you bottom edges to get a nice smooth object. However, even if they’re tiny, they can not be printed cleanly without supports, as that second layer would have to be printed into thin air. As a work-around to still get some curvature going, you can first chamfer that edge, and then fillet the upper edge of the chamfer. Like this your fillet never exceeds the overhang angle of the chamfer.
Fitting parts
Clearances between parts that need to be fitted together can be tricky to get right, as not everyone has equally well-calibrated printers and filament settings. I find it better to err on the cautious side, as putting a drop of glue in a fitting is a lot easier than sanding down parts that won’t go together.
For a press-fitting I might go as low as 0.05mm clearance between parts for my own printer, to be on the safe side 0.1mm should be alright on any modern printer. For a print-in-place moving parts I would increase that clearance to at least 0.2mm, all it takes for it to be seized solid is a bit of over-extrusion or slightly too little space between nozzle and bed.
I recommend chamfering the edges of the object that needs to be inserted into another. Corners are the areas where an FDM printer is the least precise due to the thickness of the lines and the direction change of the print head. Chamfering the edges on the insert creates more clearance at the corners.
For inserts into the side walls of our objects, shape and orientation are key. Here it’s especially important to avoid supports, as supported areas will never be as precise as those that don’t require them.
While you can try to count on your printer’s ability to bridge those areas unsupported, it’s best to avoid the problem altogether by picking the right insert shape.
I’ll leave it at this for now. If there’s any interest in this, I’ll be happy to write up some more. Let me know.
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. Suggestions only. Below is what I mean by “kickstand”. In some cases it works well. Not all cases.
