3DP optimized buckle

Prior art

• a lot of 3DP buckles I found still required supports, often because they were simply side release buckles, whose typical design require supports & work better with the better (relatively speaking) isotropy afforded by injection molding

  

• even the robust buckles model still requires support

  

• this design doesn't require support, but I had some doubt about the strength – by appearances, a bunch of load goes through layer adhesion across a relatively small perimeter (unless printed at 100% infill, in which case it's a relatively small cross section)

  

• this center release buckle is a lot better than the previous, but still relies on layer adhesion for strength

  • note: at some point there is sufficient layer adhesion that it is no longer the limiting factor in strength

    

Summary

• this design was intended to be more of a thought experiment & as of 2024-04-01, I have no real plans to print & test it

• related design of mine, terminating in a hook

• all versions prior to V2 are very exploratory & probably not functional

Considerations

• provisions for webbing, much like this other design of mine

• ease of release & connection

  • this is doubly important for connecting straps under tensile load, where a twist lock could be very cumbersome

  • twist lock example

    

• 3D print optimized

  • no supports

  • strength

    • stresses should be located in favorable scenarios

    • snaps & flexures tend to work much better in plane – flexures should be printed parallel to print bed

• parameterized

  • design largely driven from few dimensions

Parameterization

• revisions 1-2, at least, use the slot length as the principle driver for nearly all other dimensions

Revision 2

• note the 0.5 mm D TAIL LENGTH CLEARANCE on both sides ensures the snap latches over (later discussed)

• inspiration for this design borrowed from my previous work here

Dovetail profile

• to fasten the 2 parts together, we need to immobilize all 6 degrees of freedom

• dovetails are a great, very strong way to immobilize 5 DoF

• furthermore, dovetails don't require supports

• in this embodiment, 30 deg overhang angles are used

MALE plate

• the last DoF, translation, is locked by the use of a loop snap fit

• the flexure length is 44.5 mm, as shown below

• in this way, the stress is tensile when the joint is loaded normally

• this is advantageous because little bulk is required to achieve considerable tensile capacity for typical 3DP filaments

• the clipped end is held in shear relative to the 2 legs which form the loop

• the compressive stress borne by the FEMALE plate is across a large face that must exist anyways to achieve the basic function of connecting to webbing

  • in thinking about this problem, pretty much any other method of retention requires an abrupt change in cross section across the thickness of either plate, which then means layer adhesion carries a more significant fraction of the load

• releasing this buckle is as simple as flexing the “latch”

Challenges with side release architecture

• I eschewed side release buckles for a number of reasons

  • snaps being released by squeezing (like the typical side release buckles) concentrate stress across small lands of adhered layers & require supports to develop the enclosed cavity which immobilizes the same 5 DoF as dovetails do

    

• snaps released by spreading suffer from a usability problem: it's no longer a 1 handed affair to spread the snaps to disengage – example here

  • without some other mechanism to make it a 1 handed affair (which could be more parts & complexity), ease of use is quite poor

    

Future improvements

• male & female plates are not uniformly thick & consequently webbing sits at different heights under tension

• ease of connection

  • the layout as shown presents the flexure first, then the dovetail second

  • it would be best to present the dovetail first immobilize more DoF sooner

  • still not as good as an injection molded side release buckle

  • a lot of side release buckles are symmetric in that either side can be rolled 180 deg (about the axis of connection/disconnection) & still latch correctly

    • this buckle, as of 2024-04-03, given the way the webbing is supposed to route, precludes the latch from working in both orientations