Grip6-inspired belt buckle

Objectives (which this meets):

• no metal
• strong and smooth (print flat, then bend; details below)
• work with any strap/webbing (sew/snap insert connects belt to buckle)
• minimal thickness, with no lumpy stoppers in the back; it's really hard to get lower-profile than this buckle
• easy to swap belts/buckles

Instructions:

Printing

If you orient the parts as shown in the photo, then you don't need supports, and the bending form will be very smooth.  If you print the bending form flat, it will have nasty layer lines.  That probably doesn't matter, but I didn't want them transferring to the buckle later.  I printed in PETG and it's been holding up great.

DO NOT POP THE INSERT INTO THE BUCKLE YET.  If you snap in the insert without sewing it to a belt, you have no way to get it back out of the buckle.  I made a test-buckle with a hole so I could pop it it out from the front.  You could probably just wrap several loops of thread through the holes if you really want to test the fit.

Bending

I tried a few things, but the following approach was the easiest, most foolproof, and produced the best results.

1. put the buckle in a coffee cup (you can use a bowl, but it will make step 4 harder)
2. boil some water, then pour it in the cup
3. wait 10-20 seconds and/or watch for the buckle to start deforming a bit
4. using some kitchen tongs, remove the buckle from the water (be gentle so you don't dent it)
5. quickly press the buckle into the bending form, and run it under cold water in the sink.  You can use your fingers for this; the buckle is hot, but it's a horrible conductor.

That's it.  I'm gonna use this trick in future models.

Sewing

Sew the insert onto the end of the belt.  You may want to burn the end of the strap/webbing so it doesn't fray.  Mine is cotton, not plastic, so I just put a little CA glue on there.  I used white thread so you can see it in the picture.  Orient the insert so that the bevel faces the short end of the belt, and the recess faces away from the belt.  This recess provides space for the thread so it doesn't interfere when you insert it into the buckle.

Assembly

Feed the belt through the slot.  Insert the beveled side in first, and then snap down the rounded side.  To remove the insert, just feed some belt back through the slot, and pull up on the rounded side (closer to the slot).  You can easily mix/match belts and buckles this way.

Wearing

The belt is fed in front-to-back on both sides, for a very clean look.  It takes a little familiarization to adjust, but I learned quickly and it's really easy to dial in the fit.  The buckle is very secure.  I mean, daily-use secure, not “on belay” secure.

Modification

• wider/narrower belt - stretch it in your slicer
• more/less curvature - stretch the bending form in your slicer
• insert tolerances - stretch the insert width a bit
• anything - I've included the FreeCAD model.  Almost all dimensions are driven from a spreadsheet, so it's easy to modify.