3D PRINT STRONG locking bracelet

by profhankd, published

3D PRINT STRONG locking bracelet by profhankd Mar 1, 2015
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This is a simple variant of a locking bracelet I designed for the Engineer's Day Open House, February 28, 2015, at the University of Kentucky. The version handed-out from my lab had the UK logo on it, this one has the words "3D PRINT STRONG" on it... and strong it is! Despite printing in PLA just 2 layers thick, the tiny interlocked-3/4-circles can hold scary weights without unclasping: note the photo with the fish scale confirming it doesn't even come close to unclasping at 21 pounds of load.


This is a very easy print, spiralized in 0.25mm PLA on a MakerGear M2, except for the fact that it might not like to stay attached to the bed. Printing it with a 3-strand brim helped a lot; it takes about 5 minutes to print and uses about 3g of PLA.

This is a one-size-fits-most bracelet, so resizing shouldn't be needed.

The first photo is just the 3D PRINT STRONG version in white. The second shows both the original UK version and this version. The third was a load test of a slightly bad print of the UK version -- even the bad print was able to withstand huge loads. I put the bracelet on a piece of wire rack, and even with my fish scale's hook creasing the bracelet, I couldn't break the clasp mechanism open. The photo shows the scale at just 21 pounds because I took the photo while pulling down on the scale, which is harder than it sounds. ;-)

Incidentally, to unclasp: push the sides of the bracelet in a little and the rings will unhook. Easy.

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I did the original design in OpenSCAD but didn't post it yet because I didn't have a good way to do arbitrary markings on it in the customizer. The proportionately-spaced "text" you see is actually an image run through my free trace2scad tool, http://aggregate.org/MAKE/TRACE2SCAD/ (which still requires installation; I plan to do a WWW interface version so people don't need to install anything). My OpenSCAD code is a bit more complicated than yours because it allows marking with arbitrary images and handles sizing in a more complex way (it keeps thickness constant all around the bracelet and I have variants allowing for compensation of the gap distance between the clasps, which makes the shape more complex). Anyway, I came up with this locking mechanism while devising some vertical print-in-place hinge designs (to be posted soon, I hope) and posted it in this STL form to get it out quickly. I figured this type of mechanism should be useful not only for bracelets, but for cable organizers, quick-release mounts, etc. -- I expect more people will end-up using the idea in other devices than printing the bracelet that demonstrates the lock concept....

So, I have no problem with derivatives of any kind and your OpenSCAD code looks fine except for the Thingiverse-jumbled formatting. ;-)

Hate following a spammer with a comment....
I like your bracelet but wanted different text, so I wrote it in scad.....
I'm not going to post it as a derivative. Pretty simple code. I'm sure pasting it here will ruin the formatting but here it is:(yep. some weird stuff)


text="Arvin's Sweetheart";

printerW=0.4;//filament printed width
layers=2;//this times printerW gives thickness of the bracelet
scaleL=50/75;// w/l %

cutRing(d=width, h=height, t=thickness, g=gap, s=scaleL, $fn=100);

translate([width/2*scaleL-thickness, -gap/2+hookD/2-thickness, 0])

translate([width/2scaleL-thickness, gap/2-thickness2, 0])


module cutRing(d, h, t, g, s=1){
cylinder(d=d, h=h);

    cylinder(d=d-t*2, h=h+2);

    translate([(d/2-g)*s, -g/2, -1])
    cube([g, g, h+2]);


module hook(d=hookD, h=height, g=hookGap, t=thickness){
cylinder(d=d, h=h);

    cylinder(d=d-t*2, h=h+2);

    translate([0, 0, -1])
    cube([g, g, h+2]);


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