Recently a friend sent this lovely turntable across my desk looking for a bit of TLC. Yes, it is a little worse for wear, but except a couple missing parts it all still works. One of those missing parts is an adjustable foot for leveling the table, while the three remaining feet had all been damaged and were beginning to fall apart; look closely at the foot that’s removed in the above photo and you can find an epoxy seam where it was repaired once before. Below you can see my final part with steel bolt for threading next to the fully 3D printed prototype:
I think this is a good time to mention how much I love McMaster-Carr. No, I am not a paid spokesman, but for years that website has been a bottomless receptacle for my time. I can’t be the only one who flips through random hardware collections in hopes of finding inspiration for a new project… right? I digress, my reason for mentioning McMaster is because their site is a wonderful source for hardware models. Certainly not for everything, but a good majority of things you want to include in assembly like fasteners, belts, pipes, pulleys, bearings, etc, have CAD files available download. Initially I was hoping to use the fully-printed part as the end-use piece so that’s how I began modeling, I’ll explain why I went with a steel thread later. Regardless if I plan to include threaded hardware or want to model threads for 3D printing, this is always my first stop. Once you find the hardware you need click on the part number from the list, then if you see their CAD icon next to the link it means there’s a downloadable file available (shown below):
After measuring the thread size on the original part I download a corresponding model to work from as reference. Once the modeling of the foot part was far enough along to include the threads, I created a new assembly with the foot and the bolt for reference together. Here you can see the turntable foot rolled back to before I began modeling the thread, and then the finished part by comparison:
There’s really no magic behind this, just follow the feature tree from your reference part and adjust the dimensions as you need. Notice the small fillet around the base of the thread, this creates a stronger transition point and reduce stress concentration to prevent the thread breaking off. I also shrank the outer diameter of the thread by .2 mm for tolerance, and left the edges of the thread slightly blunted for better print reproduction. Shown below is a comparison of the metal thread (grey lines) overlaid on the model for print (black lines):
Time to print. This part was done with progressive layer resolution increase through Simplify3D. The vertical side with the texture pattern was printed at 150 micron, while the curved transition portion between the base and the thread was 100 micron, and the threads themselves 50 micron. I will talk more about how I setup these prints in a follow up post coming soon.
The photo above shows the part printed in PETG as it came off the print bed of my MAKEiT Pro-L, with absolutely no finishing work. Below you can see it fit straight away into the threading on the table:
Despite being happy with the overall fit and finish, I expected from the start that the printed threading wouldn’t stand up to long term use. The turntable is deceptively heavy, a bit over 20 pounds, and I didn’t want one of the threads to snap off and get stuck inside if someone moved it too gruffly. Onto remodeling the foot to include metal threading.
With the foot saved as a new name I deleted the threading out of the feature tree and began cutting away material for the bolt to fit into. I left about 0.2 mm tolerance on all sides around the threads of the bolt, but I wanted a more snug fit on the hex cap. Since the weight of the table is going to be pressing down on the bolt it needed to be secured with a little bit of trickery to keep it from popping out of the foot. Starting with a 0.2 mm tolerance, the extruded cut that cleared space for the bolt head has a 2 degree draft, meaning as the bolt is inserted the tolerance closes down and tightens around it. Small tabs were then modeled to create a solid snap-fit, shown below:
Above you can see the bottom surface of the print and how the bolt finally inserts into it. Still, there’s one final step to really get the high quality finished part I was looking for, simply adding an adhesive-backed foam pad:
You can draw your own conclusions from here, but it’s my opinion that this 3D printed replacement is at least as good as the original, if not better:
The table is still in need of a bit more TLC, but at least one impossible to find part has been replaced and we are one step closer to hearing Jimi as it was meant to be heard.
More to come on the turntable project soon, including a detailed write-up of how to achieve the amazing print quality shown in the photos.