Optimized strong 20mm strap tensioner

Use case:

You may know the tensioner on the free ends of your backpack shoulder straps.  You pull the free ends down to tighten the straps. Ideally they stay exactly at that length forever. To release the straps, you pull up the lower end the tensioner about 45° and the straps start to slip through. 

I love the 20mm wide nylon straps that are easily and cheaply available online. They are great to strap things down on your bicycle or motorbike and I strap my GoPro to trees or posts when I want to catch a static scene. For such applications it is important that the strap can be pulled tight strongly and that the densioner does not let go under high load. 

This is exactly what this part does, but it does it very well. There is actually a fine line in the design between too edgy and too loose. If the edges are very sharp and the overhang on the final edge is too wide, you will not be able to pull the strap really tight. It starts to jam when a certain tension is reached. If the edges are too soft and the overhang is a bit less, your strap may start to slip through at high loads. After quite some experimenting, I am very happy with this design now, I hope you are too.

Printing

Printing of this part is very easy. Put the model on the print bed in the uploaded orientation. Use 4 or more perimeters to make it strong. For the remaining infill 25% is enough. No supports are needed. I strongly recommend PETG for functional parts, but I have tested this part successfully from PLA as well. 

Assembly

Make sure to bring in the straps like shown in the picture, it will only work in this way.

• Turn the part upside down after printing. The side that touched the print bed needs to point upwards. The flat, rounded finger handle needs to point to the left. Use the cover picture as an example. 
• The left side is where the tensioner needs to be fixed in a closed loop of strap. That loop can be sawn, glued or closed with this non-pullable tensioner: https://www.printables.com/model/121221-strap-tensioner-load-optimized
• Make sure that both ends of this closed loop enter the tensioner from the bottom side (the right and the middle slot).
• The strap that can be pulled tight needs to come from the left, enter from the bottom side through the middle slot, go over the triangular bar and exit through the left slot towards the bottom. 
• In the end, things need to look as clean as in the picture. All straps come and leave from the bottom. Under load, the tensioner will stay flat.
• Now you can pull on the free top strap (the upper one) on the left side, it will pull the lower strap through the tensioner. Under load, but also under no load, it will not slip back.
• To release the tension, lift up the left part of the tensioner. Once lifted to about a 45° upwards angle, it will start to let the left strap slip free. 

Please like it if you like it

Your satisfaction is my reward. Please leave a like if you like this design. 

Disclaimer: In all my testing the tensioner did not break and did not let the strap slip under load. But your results may vary, use this part at your own risk!