I have been doing some research into yoyo design, and have been having fun working on a few designs. I have many years of CAD experience, and was exploring what kind of dimensional tolerancing others use.
I was shocked to read that multiple sources indicated that some dimensions are held as tight as +/- .0002" to +/- .0004". I would consider +/- .005 a normal “tight” tolerance, and that what is suggested is 10X as tight! Are yoyo halves really expensive to produce? Why so tight?
Anyone have insight into this, or has tried to produce a less-tightly toleranced yoyo? Thanks for the help.
My guess is parts like the bearing seat, or rim fitment on multi material has to be very dimensionally sound to eliminate vibe. A looser bearing post will introduce vibe, and a bearing post thats too wide just wont work. I imagine you can get away with looser tolerances if you’re fine to have some vibe
Yep I was just having a discussion about this. In metric I had a shop produce some halves with +/- 0.05 and found out after the fact that this tolerance only really works for responsives (good thing mine is responsive). Talking with @Lotaxi who machines yo-yos he suggested that 0.01 mm is the minimum tolerance for unresponsives to ensure a good fit with minimum vibe.
It might be that I’m just in that particular niche of machining, but ±.005" is a pretty standard tolerance to me. Not exactly wide, but routine enough that I don’t really need to think about it to stay in spec. A .010" window is a mile wide. ±.0025" is where I’d start to consider something on the tighter end of things, but a .005" window still not too hard to hit.
I get paranoid and meticulous about everything when I get under ±.0015" or so. Holding total runout along an 8 inch shaft under .003" (±.0015" deflection from a cylindrical datum in any direction at any point) is scary, for example, where holding the diameter of a feature to ±.003" is trivial.
You only really need the tight tolerance (under ±.001") when it comes to coaxiality of the cup and profile and the fit of the bearing on the seat post.
For the cup/profile coaxiality, you obviously need everything to be balanced properly at a few thousand RPM, so that’s where the ±.0002" comes in. It’s not super hard to hit if you’re setting your parts up right and you have a robust fixturing solution, but it’s the kind of thing you’re actually going to plan for in fixturing and pay close attention to as you’re loading parts. I make custom fixturing for every design I cut.
As for the bearing post, you need to hit a locational transition fit (Class LT1) to keep things properly stable. A running fit (RC) or a looser location fit (LC) are going to allow the bearing to slip and shift, causing a state where your halves might become eccentric and thereby become an asymmetric mass vibrator. I think a lot of the Chinese manufacturers just take the guesswork out and use a light drive force fit (FN1).
Those are the only 2 truly critical tolerances in a monometal yoyo, as far as I’m concerned. Bimetals or multi-piece designs are going to require proper fit calculations for all the relevant components, but they’re a separate matter. Keep yourself within the range of an FN1 or FN2 force fit for a bimetal ring and things should stay pretty happy as long as the coaxiality tolerance described above is observed.
Mass is important, but you can have a yoyo come out a little too heavy or a little too light and still have it play properly on the string. The characteristics might be a little different than envisioned by the design, but it’ll function properly. Same with diameter and width.
Kinda yes and no? I’d say they’re more expensive to set up and measure than they are to run properly. Once your machine is set, the CNC will keep things happy as long as you’re paying attention to how you’re loading the machine.
Keep the 2 main tolerances intact for unresponsives or you’ll have bad outcomes.
Responsives don’t need to stay vibrationally stable for long periods of time. They need to be stable enough that they’re not uncomfortable to play at the end of the string and they need to return to the hand when called. They are also usually considerably thinner width than unresponsives are, which makes them MUCH more modally stable along the axis of rotation and therefore more tolerant to sloppier fits.
I’m always around to answer questions, if you’ve got them.
Thank you so much for this info. The limits/fits for the bearing seat is what I was looking for.
Question about the coaxiality of the cup/profile. Can you explain more about this? I am very familiar with position/profile tolerancing, but do not deal with runout/coaxiality very much. Are you saying the dimensional values are less important the the form/coaxiality of the finished product?
I think the most important takeaway of what I was talking about is that the guts and the profile/cup need to be in proper alignment. If there’s too much of an angle between the axes along which they were cut, the unit will not be balanced, right?
The way I have to cut my yoyos is fairly different than a lot of the large production companies. The spindle in my lathe doesn’t have a particularly large bore, so the typical 2.25 inch diameter stock that a lot of yoyo designs use won’t fit through it. I have to cut preform stock chunks out of larger lengths of material. I then put those chunks into a custom-bored collet and cut the cup. Then I cut a shoulder into an expansion collet and fixture inside the cup to cut the profile and guts.
If I’m not careful with how I fixture the yoyo when I flip it around, I can mismatch the cut axis of the cup and the profile/guts and have an unbalanced yoyo as a result. If a production factory isn’t careful, the guts can be misaligned to the cup/profile to the same effect.
When I say this, I mean specifically that a shift in form does not destroy functionality. If a yoyo is a gram and a half heavy or light it might be noticeable in how the yoyo feels and moves through your routine, but only compared to other units of the same design that are far away in measured mass. If it’s .005" or .010"" smaller on the diameter or width you likely won’t notice it at all in the hand. If you have an axis mismatch large enough to unbalance the rotation? You’ll feel that vibe.
Is that the info you were looking for, or are you looking more for what exactly I’m talking about when I say “axis mismatch?”
Recently tried to remove a bearing from one of my yoyos, only to discover that the inner shaft that the bearing sits around is very slightly too large. It took me more than 5 minutes of failed prying, pulling, and banging to get that pesky bearing out. It even snapped the end of my needle off as I tried to pry it loose. I suspect it snuck through the QA process by appearing to fit.
Was it a… CLYW? If so that’s “by design” whether I agree with it or not.
Some places purposely oversize and cram a bearing on in an effort to reduce vibration. The downside to that is you can’t even take it apart without risk of inducing said vibration.
As @AudreySickburn said, this is likely by design. A force fit is going to confirm bearing alignment by default and remove the possibility (and consumer accusation) of vibe being introduced through a loose seat.
One thing you can try is to leverage the properties of thermal expansion. Aluminum shrinks a fair bit more than steel when it’s cold. Toss the thing in the freezer for an hour or so, see if it changes anything.
Another thing you can try is to take an ice cube and press it to the hub inside the cup. Aluminum transfers heat WAY faster than steel, so the aluminum will shrink before the bearing gets too cold and shrinks with it.
Biggest no-go is to lose patience and pry. you want the bearing to come out as parallel with the bearing seat as possible. If you’ve got the right size drill bit or a purpose-made removal tool you can wiggle very slightly and gently with the tool inside the bearing as you pull, but prying the bearing up is likely to damage the shaft quite badly as the bearing races are much harder than the aluminum.
Best practice in all cases is to be exceedingly patient. It can be a slow process.
DANG2. Out of about 20 One Drops I removed bearings from that day only 2 had this issue (both were tapped axle), but the other one with a stuck bearing was nowhere near as bad. A little pulling and it came out with no fuss. I highly doubt that it’s an intentional part of the design for only 2 random yoyos. I think both were 7075, so that might have something to do with it.
Exactly, I reckon it was probably just a missed slip in manufacturing tolerance. When putting the bearing in it just feels like a firm fit. It would be something you only notice if you tried to remove the bearing thereafter.
Here is an example of what I believe is a non-One Drop flat 10ball, which has been living in one of my yo-yos for some time unbeknownst to me. I’m not even sure which yoyo it came from because I was pulling a lot of bearings without inspecting them first. Everything about this bearing is all wrong. The colour is dull and it doesn’t have the mirror shine of stainless steel, it has those parallel grooves on each side of the body, its C clip is too small and has sharp edges, and the shields have these 3 weird dents on them which I mistook for damage before seeing that they were equidistant and present on both sides.
