Proper design to create a good part to part fit

I posted a related topic in the slicer forum. I am working through a design that includes two PLA prints to friction fit, and one PLA print that has a indent to fit a Raspberry PI board. I am looking to create a fiction fit for both. I am having trouble getting the fit right and would like to know if anyone has suggestions on how the part dimensions should be adjusted to get a good fit. For example, should i use the exact dimensions off the mechanical drawing of the RPi or increase the opening by a few tenths to allow for variation or tolerances. Any tips would be welcome. Similar question when i am joining two printed parts. For example if i created a groove of 2 mm should the width of the mating piece be exactly 2 mm, or reduced by some amount.

I find what works is purely dependent on how your printer is tuned. For me it is based on my nozzle diameter. So if the hole is 10 mm the diameter the dowel that would go in it would be .04 mm smaller as a starting point then fine tune the dowel (or hole) diameters. In Cura there is a setting for horizontal hole expansion (or reduction if it is negative value) that works nicely too, but only in the horizontal plane.


Also square holes is another story since on my printer there is a slight budge at the sharp corners that comes into play. I have and Ender 3 Pro and that is known issue on stock machines. More advanced machines that can be tuned out.

Yeah. like @Larry_Bowers said. A proper calibrated printer is key.

This also mean all axis need to be calibrated or printing the counter part in a different orientation will not fit.

If you need parts to fit into each other, you need tolerance to be build in.

I always use 0.1mm per length or 0.1mm on a radius, when I design such parts. This will properly compensate the round filament sausages stacked on top of each other.

Thanks! this is super helpful. I have a box of useless parts as i have been doing trial and error to this point. Your guidelines will be most helpful

I’ve had good success following the instructions in this YouTube video from Lost in Tech:

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