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Articulated Figure : In place or separate printing for moving joints?

So in-place printing is the “holy grail” for 3D printed designs with moving parts. But is in-place the best option in all situations, specifically for small moving joints that could be used in a small (150mm) articulated figure?

Aiming for a model of that size I estimated that the joints would need to be a cross-section of 10mm x 10mm. The shafts (pins) what would allow rotation would be 5mm in diameter. A simple joint design would be as shown to the right, allowing for the joint to flex a full 180 degrees (and so be good for arms and legs).

This model splits down into three pieces which I'll call the link (shown in blue) and parts A and B (shown in red and green). It's worth noting that part B is just a mirror of part A.

To print this joint as separate pieces just needs the model separating.

I found that the joint worked best when the holes were slightly bigger than the shafts. The diameter of the hole was 5.05mm and the shaft was 5.00mm; this allowed the pieces to be fitted together easily but maintained a level of stiffness that an articulated figure would need.

I also added a slight bevel to the ends of the shafts to make them easier to fit.

No other adjustments were needed to the model.

To print in-place required a bit more work on the model.

To stop the parts fusing together during printing touching walls needs to be separated. I found that a distance of 0.3mm worked.

This gap was also needed for the holes, meaning they now had a diameter of 5.6mm.

After printing and the satisfying “snap” when moving the joint, the joint itself is looser than the printed-separately one. It's easy to see why, that 0.3mm gap around the shafts isn't tight enough.

Comparing the two joints, the printed in separate pieces is on the left and the print in place on the right. You can see the shafts are a much tighter fit on the printed separately. So for a small articulated figure, it's looking like avoiding in-place printing is the best option if you want stiff joints.

Printed on a Bambu Lab P1S, 0.4mm nozzle, Smooth High Temp plate, 0.16mm Optimal quality.

in-place_versus_separate_prints_for_moving_joints.txt · Last modified: 2024/02/01 18:44 by jasonh