Apr 17, 2015

pin-pivots to improve snap-together 3D Printed parts

After lots of experimenting with snap-together parts, I decided to try another method of connecting multiple parts - a pivoting pin. The idea came from Paul Gross (thanks!) in a comment on my Google+ post - and I decided to start from scratch to design something.

The benefits I was hoping for compared to the snap-together model were mostly to get easier construction of multiple parts, a smooth pivot and less accidental separation when pressure was applied to the joint. The other snap-together part designs I came up with were pretty good, but far from strong-holding or easy-to-connect.

Design Highlights:

There were certain things that I learned in this design worth sharing, even if you don't care about the details (which are all TL;DR below)

  • The gap in the pin needed to be wide enough at the tip to allow it to compress enough to get the wider tip through the narrower receiving hole.
  • The whole bottom side of the pin needed to be flattened to provide a flat bottom for the bed (think about what the pin head would have done to that if it too were not flattened) and to help with bed adhesion while printing
  • The top side of the pin legs were flattened just to simplify the printing and reduce the surface area of the touching parts when inserted and pivoting.
  • The measurement from pin head to pin insertion tip needed to approximate, but not be less than, the space between the receiving holes (so there's not too much lateral motion of the pin).


This design works well! It provides a smooth pivot, doesn't take much effort to insert, and doesn't separate too easily. That said, this is not a perfect connection. A bit of push on the tip of the pin, and it will unclip and start sliding out - but it takes effort - and in connections where the tip of the pin is mostly behind other parts, this is not likely to happen. I have not yet tried to print lots of pins in one print job, but hopefully that will work well. NOTE: This design is probably NOT safe for kids under 3 yrs old, as the pins are clearly small enough to swallow (and they are not delicious).

Soon I'll post some actual useful objects I plan to make with this design. First order of business, another name bracelet for my daughter ;)

Design Details:

The receiving side of the equation was simple - a couple of aligned holes to accept the pin. I started with a radius which would give plenty of room to receive the pin without binding so the parts would flex easily around the pin when connected. The measurements I used were 2mm Radius on the receiving hole with 1.5mm radius on the pin. That provides 0.5mm gap on all sides - plenty of room for printing precision issues. On the pin ends, I had to go larger than the hole to keep the pin in place once inserted. On the head which would never have to enter the receptacle, I went with 2.4mm radius. On the side of the pin which would be inserted, I went with 2.2mm - and cut a gap of approximately 1.2mm at the widest, which narrows to zero as you go toward the pin head side.

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