I’ve been messing around in Onshape trying to design a yo-yo, but I’ve hit a wall. I keep seeing people talk about tolerances when it comes to bearings, but honestly… I have no clue what that means or how to figure it out.
I understand the basic idea of putting a bearing seat in CAD, but when it comes to the exact size, how loose/tight it should be, and how that translates from CAD to real life, I’m totally lost.
If anyone could explain this in beginner terms or point me to a good resource, I’d really appreciate it. I don’t want to mess up my design just because I don’t get how bearing fits are supposed to work.
Tolerance in design refers to an acceptable size range expected during the machining process. Say a spec for the inner diameter (ID) of the bearing is 6.35mm, you’d want to make the seat slightly smaller, I’m guessing (never designed a YoYo so…) 6.25 +/- .05, the +/- .05 being the tolerance you allow for the realities of machine work being not always completely precise.
There are actual machinists and YoYo designers here who will hopefully chime in with more knowledge
+\- .0007in (.02mm) is the acceptable range for machining tolerances w the bearing post. And yeah tolerance is how accurate the machine can produce your design.
This YouTube series does a pretty good job of explaining what you’re after, and probably has a lot of other good advice that you might not have even thought to ask about:
Think of CAD as “Perfect”, your design intent. Both the yo-yo and bearing need to be manufactured and in doing so, you’ll receive a “Range” of sizes. Each bearing post on the yoyo halves will be slightly different (“Tolerance” is the allowable range that you specify on each feature). The bearings also have a range of sizes. If you take a yoyo half that came out kind of LARGE and a bearing that was kind of SMALL…. You get a tight fit, maybe no fit at all. The post (cylinder) needs some amount of clearance to make its way into the bearing.
Note that “Perfect” (CAD) may not be right. You can design a bearing seat incorrectly for size, form or location and nothing is going to fit.
Adding on to what others said, I believe (correct me if I’m wrong) the dimensions in your CAD file should be perfectly what you intend. It’s when it gets made in the real world that tolerances come into play. It might not turn out exactly the way you intended. This is why if you are designing you need to keep these tolerances in mind in case of the worst case scenario the parts still fit together.
However anything a Yoyo is being machined on should have tight enough tolerances so I don’t think you really need to worry about it. Design it in CAD to be perfect and in the real world the Yoyo will be slightly off but due to the tolerance that’s it’s machined in it should turn out fine if you had the right dimensions in CAD.
Depends on what you mean by intent. Your intent should be to have design dimensions in the CAD file that account for the machining tolerances, especially for parts that fit together, like the bearing post. If you’re designing for a C bearing, which has a spec’d ID of 0.25”, you don’t want to design your bearing post at exactly 0.25” OD. First, the bearing manufacturing isn’t perfect, an ABEC-1 bearing for example could have a ID that’s +/- 0.000295” off. Similarly, the manufacturing of the yoyo won’t be perfect, and there will be runout typically similar to the bearing tolerances (but also depends on the shop and how much you’re willing to pay for precision). Let’s say the shop is guaranteeing to be within 0.0002” of spec, and the bearing post ends up 0.0002” larger than design. It’s still within spec, but over half of the bearings out there won’t fit on that post. As a general rule of thumb, you should add the tolerances of the bearing and the machining of the yoyo, and design your post at least that much smaller. In the example above, your CAD drawing should show a bearing post that’s 0.25” - 0.000295” - 0.0002” = 0.249505” (+/- 0.0002”). This guarantees that any yoyo post machined to within spec fits any bearing that was made to within spec.
Except usually the CAD drawing only shows half of the yoyo which is then revolved around the central axis, so the dimension on the drawing is actually the radius rather than the diameter, so you’d draw it as 0.1247525” +/- 0.0001”.
Also, none of the above accounts for anodizing, which will also add thickness to the bearing post which needs to be accounted for in the design.
The first video in the series I linked above probably describes this better than I just did though.
Hey everyone, I was AFK for a bit, but thanks so much to everyone for breaking this down! I really appreciate the explanations and the examples. Also, thanks for the videos—somehow I hadn’t found these after searching YouTube for “how to design a yo-yo.” They’re super helpful and made a lot of things click for me.
Interesting conversation and some good points. Here’s how I do bearing POSTS. Start off with the nominal inside diameter of our bearing which is .2500”, but we know that the ID is actually about .0002” smaller than that, so .2498”. Then, we want our bearings to be user serviceable(we want a slight slip fit), so we subtract another .0001” that gets us to our Final Bearing Post Diameter of .2497”. Working closely with our anodizers, and after testing some pieces, we know that their ano “build-up” is going to be between .0000 and about .0002”, but we also want to account for the occasional ano batch where they add a little extra(maybe because 7075 or 7068 behaving differently) so we subtract another .0001”. So out at the machine(pre-ano) I’m aiming for a bearing post size of .2494, after ano it will be .2494/.2497. My machine, as all machines, experiences thermal growth and tool wear during use so that .2494 has a bit of variation as well. None of this addresses cylindricity or runout, a totally different conversation.
