My folding moon chair that was great for lounging around, and folded up nicely when I needed to tuck it away. One day, one of the plastic brackets that supported the legs broke. Since I recently got a 3D printer to play with, instead of throwing out the entire chair, I created a 3D Printed Bracket for a Folding Moon Chair.
The first step is the remove the broken bracket. All the brackets and pivot points on these type of chairs are fastened with steel rivets. I used a drill with a drill bit that’s slightly larger that the hole in the rivet to cut through the rivet end. Once the end is drilled out, the rivet slides out from the other end.
You can see my earlier attempts for a quick fix with epoxy. In short, it did not work. The epoxy basically cracked when I first sat down. I kinda knew it wouldn’t work, but was hoping I didn’t have to take the whole bracket off.
Making the 3D Model for the Bracket
In order to print the bracket, I need to first create a 3D model. I made some quick measurements of the broken bracket and drew up a model in FreeCAD.
I added chamfers to reduce stress concentrations at the inside corners.
3D Printing the Replacement Bracket for the Moon Chair
When setting up my model for 3D printing, I used a 20% infill with 5 layers for the shell, top, and bottom. I find a higher shell thickness, and not necessarily a higher infill added to the strength of the part.
The 3d printed model is not an exact replica to the original. I’m not sure what kind of plastic the original bracket is made of, but the PLA I’m printing with seems to be a bit more brittle. I made sure the important dimensions were the same, such as the location of the holes, spacing for the tubing, but otherwise, tried to beef-up the rest of the bracket.
Installing the 3D Printed Bracket for the Folding Moon Chair
Installing the part is pretty straightforward. Instead of using rivets, I used 6-32 machine screws and nuts to put it back together. If they loosen overtime, I may add some Loctite, or change to nuts with nylon washers.
The bracket fit surprisingly fit just like the original on the first try. I can even fold it up as designed. If I had printed it in black, I doubt anyone but me would notice it was repaired/replaced.
Overall, I’m pretty happy with this quick project. Being able to repair something instead of throwing out and replacing it, and using my 3d printer for something practical is empowering.
Prior to owning a 3d printer, creating complicated features like this, either by milling it out of aluminum/plastic, or by welding some metal together would have taken a lot more time and effort. Now, I can send this to my printer and have a part ready to go. In the future, if I have other projects that require metal parts, I could test fit/function with a 3d printed part first, before investing time and materials into machining out of metal. Having a 3D printer definitely changes the way I go about my fixes and builds projects.
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