Unresponsive bearing yoyo with weights - "C" size bearing

I've redesigned my previous yoyo to be unresponsive and accept the widely used standard "size C" yoyo bearing and standard size C silicone response pads.

NOTE: This model has an extra layer covering the hole where the bolt goes. You must cut this out to assemble it. I did this so that the outer face would be as flat as possible. Otherwise there is a perimeter suspended in the air when printing which caused a lot of issues for me, even with supports.

Parts needed that you can't print:

1. 4mm piece of threaded rod, or a long 4mm bolt with the head cut off so it's just a fully threaded shaft
2. 2x matching 4mm nuts that fit the shaft
3. 2x matching 4mm flat washers that also fit the shaft
4. yoyo bearing size "C"
5. Size C yoyo response pads (19mm)
6. 12 1/4-20 (ish) nuts. The thread is not actually important, only the weight and OD. The outer face to face distance needs to be 10.5mm almost exactly to press into the registration holes for the weights.
7. a yoyo string
8. 4mm drill bit
9. hobby knife

You can use a nut and bolt too, but for balance I found that threaded rod and nuts on both sides was much better.

I have included a step file to hopefully make adjusting the weights easier. Open it in your favorite cad software and add more weights, remove some, or change the OD to accept different nuts.

This was designed in realthunder's fork of FreeCAD so I have not uploaded the FreeCAD file as it would be completely broken in other versions. If you would like it feel free to message me however the step is probably more useful in the long run since the RT fork is starting to age compared to the stable version of FreeCAD at this point.

This model is also posted on thingiverse, my username on that platform is “aezai3eifi”

Printing Instructions:

• Supports: Yes
• Resolution: .14mm layer height
• Infill: 40% "stars" pattern
• Filament material: PLA

The infill for good balance is important. I ended up using "stars". I tested gyroid and many others but stars resulted in the most predictable balance. You might need to play with this on your printer.

I recommend concentric top and bottom infill for good balance. I tested with more standard infill patterns and things were sometimes inconsistent and created wobble.

Distribute the seam randomly. An aligned seam will cause balance issues.

Yoyo must be printed with the outside face down. And your bridge settings must be spot on. It's also a good idea to use some minimal supports for the overhangs and to keep the face where the bolt/washer rests nice and flat.

The model has an extra layer covering the hole. This must be cut or drilled out to assemble it. I added this so that the outer face would be as flat and round as possible and there would not be any corners suspended in the air.

Post Printing:

Drill or cut out the extra face covering the bolt hole

Use a very sharp hobby knife to cut out the extra layer covering the bolt hole to allow a bolt to pass through. You can use a drill too, but the potential for messing up the model and needing to reprint is much higher.

Clean up the bolt hole

Use the back end of a 4mm drill bit (not the cutting part, the solid part that goes in the drill chuck), or a 4mm metal dowel pin. Force it by hand into the hole while rotating it to clean up any surface inconsistencies. This will help center the bolt and make assembly easier. If it's really hard you could start with a slightly smaller size.

Clean up the bearing clearance and response pad pocket

Using the same hobby knife clean up the edges of all the inner pockets where the bearing and response pads go. You'll have to use good judgement here as every printer is going to leave different amounts of detritus on these surfaces. There should be clearance for the bearing, so it should spin freely when pressed onto the bearing journal, and the response pad should sit almost flush with the surface, just barely, almost imperceptibly proud of it.

It is especially important that the shoulder where the bearing registers against the face is flat and free of any bumps or imperfections. If it isn't the halves of the yoyo will not be parallel with each other and nothing will work correctly. It took me a lot of patience to get this right. If your printer has having trouble try printing slower. Clean it up as best you can with the knife.

Assemble all the parts

Don't forget the response pads. You'll need to buy those and the bearing from a yoyo parts supplier.

The axle will be a very tight fit and it might feel like you're threading it in a little bit. This is fine as long as the faces are parallel to one and other.

Align the weights

I found that despite the two halves being balanced there is some vibration if they are not exactly aligned with each other. You can do this by picking a weight on each side and rotating the halves until those two weights are in line with each other. Then fine tune it by throwing it and checking to see if it vibrates, make small adjustments, and eventually it will be pretty stable.