Pin Hinge Print-in-Place Tolerance Test - PIP - 2 Versions

When designing models with horizontal pin hinges that are print-in-place, you generally want to make the hinges with as tight tolerances as possible, but not so tight that the hinge parts are fused together. This fusing can occur if there is not enough space between the pin and the socket that surrounds it, or when the sides of the hinge are too close to each other (adjacent spacing). Filament bridging for the pin is required for print-in-place hinges. This makes it a little tricky to get just the right measurements to have a good-working, secure hinge.

There are two versions of these simple tests, one with a series of small hinges with incremental tolerances (both for the pin and side spacing) starting at 0.1mm and increasing to 0.5mm in 0.05 increments. The fine version has  0.025 mm increments ranging from 0.01 to 0.03mm. The hinge pin is 4mm in diameter, but with slightly flattened top and bottom surfaces on the pin, and with a peak in the receiving sockets (for improved printing without supports). Each hinge segment has a tab with a corresponding tolerance measurement. See the included diagrams and photos.

If you are not sure how accurate your printer is, print the 0.05mm increment version. If your printer is ‘dialed in,’ print the 0.025mm increment version.

Print the model at the slicer settings and with the filament you intend to use for a given print. No supports, raft, skirt or brim are needed. When the model is printed, see how many of the hinges will function. You might need to gently break free a tab, and then work the hinge a bit to get it to be somewhat smooth. If, while trying to break free a tab, you wind up bending the tab because the hinge piece won't budge, that means that the pieces are fused together for that amount of tolerance. It is likely that most 3D printers will not be able print with such accuracy that all of the hinges can be free. 

I printed test pieces with PLA at both 0.12mm and 0.20mm layer heights, with 100% infill. The 0.12mm layer test may have been slightly better, but the difference was relatively insignificant. My printer is pretty accurate, and I was able free up all of the hinges except for the “.1” tab. Since these measurements refer to the difference between the radii of the hinge pin & pin socket, and the adjacent spacing in the side gaps between hinge pieces, I know that when I design a model with a pin hinge, I have a rough idea that I need about 0.3mm of total separation for a fairly secure hinge that still functions (0.15mm tolerance x 2). I also now have a good idea about how much of a gap I should design in between the sides of hinge pieces.

This is a rough starting point. Smaller, larger, thinner or wider hinges could require slightly different settings. I suggest that once you have a good idea about what tolerances work for you, when designing a model with a PIP pin hinge, rather than printing your whole model, try printing just the isolated hinge mechanism to see if further adjustments are needed. This will print quickly and not use much filament.