/ 3D Printing

Snap-on Parts for Cylinders - 3D Printing Tip

Want to mount a 3D print using an existing handle or rod as a mounting point, and easily snap it on or off by hand?

snaps

It's fairly simple, but you've got to keep tolerances, the orientation of your print, the material you're printing with, and the load of what you're mounting in mind.

Here's some rules of thumb to start with:

  • Measure the cylinder you're mounting to with a precise instrument like calipers.
  • Start with a tolerance of at least 1x the diameter of your printing nozzle (typically 0.2mm to 0.4mm).
  • In order for the printed part to "snap" and hold the cylinder well, the mounting fingers need to go past being 180 degrees. Try increasing it by 30 degrees on both halves to start.
  • Make the mounting fingers 2 to 3 millimeters thick.

Here's an example in Fusion 360 employing these tips:

In this example, the cylinder I'm mounting to is 3mm in diameter. I've set the outer diameter to 6mm. My print nozzle is 0.4mm in diameter, so the inner diameter of my printed mount is 3.4mm. Note that this means the fingers are 2.6mm thick, but that's still within to suggested 2 to 3mm range. The fingers go 30 degrees into the top half of the donut on each side, resulting in a total sweep of 240 degrees. This should result in a part that's strong enough and will hold on tightly enough for most applications, and gives a satisfying "snap" when mounting the part.

For further considerations, the most important thing to keep in mind in print orientation. Much like wood grain, 3D prints resist force the best along the grain. For this application, laying the mount on its side is by far the strongest orientation to print it in.

As for material, ABS or PETG are probably the best bets, as they have a good balance of rigidity and flexibility. PLA will work, but I would not recommend it for parts that are intended to be mounted and unmounted multiple times. When you bend PLA, it tends to stay in that bent shape rather than "springing" back to its original shape like ABS or PETG. This property produces a mount that's more likely to break, and less likely to last for a long time. PLA should be fine for one-time mounts that will be glued on, however.

Past that, it's mostly a matter of trial and error. Try printing out a few tests with only the mounting donut to dial things in before doing the full print. Some further tips for trial and error:

  • If the mounting donut snaps within the first few times you mount it, try increasing the tolerance of the inner diameter. Even PLA should last a good number of snaps if the mount is proper.
  • If the mounting fingers don't hold on tightly enough, try increasing the sweep of the donut past 240 degrees, and make sure you don't have too much tolerance on the inner diameter.
  • If the mount breaks under load, try increasing the thickness of the mounting fingers, and try adding additional mounting arms to the part to share the load.