Let's talk about bearing and axle weight

Yo-Yo Mods and Maintenance
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Even though a typical monometal is made of aluminum alloy that is 2.8 g/cm^3, in the center is an axle and bearing of steel that is 7.8 g/cm^3. Since the axle and bearing are easy to swap out, changing to a different axle and bearing has the potential to change how a yoyo plays by altering weight at a sensitive location, the yoyo’s center – this is of course a feature that OD side effects offers, for example.

Specifically, I’m interesting in reducing the center weight, if possible, so I weighed some axles and bearings on the scale at work (accurate to 0.01mg) and tried swapping some stuff out in a couple yoyos that I’m very familiar with to see what kind of difference is possible.

Here are the results :nerd_face: …

Axles
5mm: 0.28g
10mm: 0.61g
16mm: 1.13g

Bearings
YYR DS (10-ball), deshielded: 1.90g
Dif-e-yo KK (8-ball), deshielded: 1.81g
BB concave ceramic (8-ball), deshielded: 1.83g
YYF center trac (8-ball), shielded: 1.93g
OD flat (10-ball), deshielded: 2.08g
YYJ flat (8-ball), deshielded: 1.85g

Notes on weights
There were rumors YYR used titanium axles. At least for their early stuff, it can be seen that maybe they were stainless steel, as the 5mm axle here came from an OG 44re:creation Stargazer. I was curious if ceramic ball bearings made much of a difference in weight but it seems like here they don’t. Perhaps a full ceramic bearing makes more of a difference but so far I’m not feeling the loud ceramic sound. All said, it seems like it’s hard to improve the bearing situation too much, as they are generally ~2g and there aren’t nicely performing materials available other than steel. However, swapping out long heavy steel axles for something shorter or a different material (titanium is half the weight of steel, for example) could be good.

Tweaking a Sparrow
I’ve been almost exclusively throwing an A-RT Sparrow for some weeks now and I’ve really been enjoying the small size and light weight. Sometimes I want a bit more stability so this yoyo is a perfect candidate to try and tweak by swapping out axle and bearing for an effective higher rim:center weight ratio.

Sparrow specs from A-RT:
diameter: 50.3mm
width: 41.3mm
weight: 60.5g

I measured the Sparrow’s axle (in the list above) and it is 10mm long and 0.61g. It’s equipped with a YYR DS bearing that weighs 1.90g deshielded. I swapped out the axle for the tiny YYR 5mm 0.28g one (using electrical tape to keep the little axle centered), and changed to a KK that is 1.81g. Center weight decreased by 0.42g.

In play, the small decrease in center weight was most noticed in a more nimble feel and lighter presence on the string. No, it’s not a big dramatic difference but the yoyo certainly felt lighter and more floaty without sacrificing stability. In fact, it feels more confident in play. After playing this yoyo for weeks, it felt fresh again. I’m keeping this change but will probably eventually get a titanium axle that is a bit longer but a similar weight as the tiny steel YYR axle that’s now in it.

Tweaking a CLYW Peak (3rd run)
So it’s crazy how big the Peak axle is, 16mm and 1.13g. We can easily swap it out for something shorter and save some substantial center weight. With a 10mm 0.61g axle in place, we save 0.52g.

Peak specs from HSYY
Diameter: 54.5mm
Width: 42.15mm
Weight: 67g

In play, there is less thunk on a throw by changing to a bit less weight in the Peak and it has a hair more speed. Here, the difference is not as dramatic as in the Sparrow, as you might expect given their respective sizes and starting weights, but it is appreciated. I don’t notice any change in its stability.

Final thoughts
I estimate that a typical yoyo has between 3% to 4% of its total weight concentrated in the center, in the bearing + axle. While there is not much of an option to change bearing weights, there is improvement to be had (maybe 0.5 to 1% weight loss) by changing out axles for something shorter and/or of a lighter material. This is especially appreciated for undersized yoyos that tend to have relatively more weight concentrated in their center versus larger yoyos. Since the center vs. rim weight is an important aspect for how a yoyo plays, lowering center weight can lower the overall weight, while effectively increasing the rim vs. center weighting at the same time.

What else?.. I’m thinking an undersize with short titanium axle and D bearing could be nice. Anyone tried the Something magnesium axles? What do D bearings weigh?

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Interesting, thats really cool. I know yoyofactory released titanium loop 2020 axles and I think they change the feel quite a bit but I’m not sure.

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Ok so there were crickets before when I tried this thread before, but watch this space…

I just ordered a Something magnesium doping axle from YYE to try in my Sparrow. I estimate that the Sparrow should weigh 0.55g less, with all of that weight taken out of the center, with the magnesium axle (and the bearing change from above) compared to the stock weight. For a little undersized yoyo that’s a pretty big difference. We’ll see how it goes…

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i’m interested…

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The Edge Beyond had a titanium axle for exactly this reason!

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Back again…

Tried a super light Something magnesium doping axle that weighs 0.15 grams. I herewith humbly submit my report:

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A-RT Sparrow with Something magnesium alloy doping axle on the left, Sparrow carbon steel axle on the right.

First off, the doping axle is an M4 8mm axle that weighs 0.15 g, while A-RT axles are
M4 10mm long axles that weigh 0.61 g. So substituting the doping axle will save you 0.46 g right in the very center of the yoyo. A potentially significant change, but let’s see how that feels in play.

Caveat that M4 axles are metric size and will not fit every yoyo. For example, my CLYW Peak uses ginormously long standard-sized axles whose threads almost, but not quite, match the M4 sizing. So you do not want to try a magnesium axle, which is a softer metal, in the wrong-sized axle thread. And in general, just be gentle with your axles so you do not strip your yoyo. Don’t cross-thread or overtighten. Ok, let’s get to it…

Sparrow with doping axle. Yo… so I was expecting to like less center weight in the Sparrow, a little undersized organic that performs beautifully for what it is, which is basically like a floaty 888 or a baby Grail. I love this little yoyo but sometimes wanted more stability that maybe enhancing the rim vs center weight could provide. The doping axle makes the Sparrow a bit less present on the string and reduces it’s momentum a bit as well. The change is admittedly subtle, but noticeable. And I was surprised that I liked it less than the feel from the standard Sparrow axle. Let’s say you take a larger yoyo like the Grail and shrink it down into something like the Sparrow. Overall, it becomes more dense and it makes sense to maintain floatiness that the rim weight needs to come up a bit. At least that’s my interpretation of the design of the Sparrow vs the Grail. At the same time, a certain amount of density is needed for a yoyo to feel present on the string so it’s not like you’re throwing air. So there’s a sweet spot of overall weight (and density) for a given yoyo size, along with its weight distribution. The Sparrow seems like it was already dialed pretty well, also considering that A-RT did two versions of it (the Jr came first), and reducing the center weight further with the doping axle has me missing the momentum and presence of the OG axle. So the Sparrow stays standard, as far as I’m concerned.

A-RT/G2 Life with doping axle. This is less noticeable and more subtle for sure. I’ve enjoyed throwing the Life quite a bit but it is more solid feeling than my absolute favorite, the Grail. So my thinking, considering how it affected the Sparrow, is that putting the doping axle in the Life would give a subtle tweak to its solid feeling. Early on, I can say that I do like the doping axle in the Life, but the change is indeed subtle, as it is less of a percentage change in weight with this larger and heavier yoyo vs the Sparrow. After playing the doped Life for a week or so, I’ll swap it back to the standard axle to compare again, and update this.

Finally, I can say that the A-RT organics are pretty dialed in terms of their floatiness and weight distributions. So swapping in this Mg-alloy axle may not improve things, as I was surprised to find with the Sparrow. I would, however, love to try a super light axle in my 3rd run Peak, as I can imagine that swapping out their huge 16mm long steel axles with a small and lighter weight axle would make for a dramatic change. Alas, they are standard-size axles (non-metric), and I don’t know a good source for a Ti- or Mg-alloy axle for them (let me know if you know of a source).

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STOP THE PRESSES! Here I was assuming that my 888 axle was standard but it’s not, it can take an M4 axle.

Just tried it but need to play with it awhile. Just imagine, though, swapping out a 20mm steel axle with an 8mm Mg-alloy one… let’s just say that the difference is night and day! Now this is the combo!..

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YYF 2008 (7075) 888 with its standard axle compared to the Something doping axle. I estimate the YYF axle is 1.2 g, versus the 0.15 g Something axle.

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How do you center that short axle?

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Short answer: I don’t center it!

Long answer: The thing is that the doping axle doesn’t have a way to adjust it since it is sealed on both sides. I could try some electrical tape or teflon tape though, but in this case this 888 tends to have a bit of vibe no matter what I do, so I don’t worry about it, and just carefully thread the axle into one side a few turns then attach the other half. That seems to work ok.

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Just as a caution I’d recommend people to be very careful when subbing out for a shorter axle that the yoyo is not designed for, I’d personally not recommend using an 8mm axle on a 6061 throw. The less threads that are holding the axle in place the more likely it is to strip.

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Indeed, good point. For example the early Yoyorecreation Stargazer was 6061 with a 5mm axle and it was notorious for stripping.

That said, I used that same 5mm YYR axle in the Sparrow. I am super cautious but do not necessarily recommend this, proceed at your own risk!

Also, to emphasize, the Mg-alloy of the doping axle is a softer metal. I do not tighten the yoyo to the same degree as I do with a steel axle because the doping axle will probably fail. In fact, the doping axle was slightly sticking in the threads (though still removable without tools) so I was bordering on overtightening it.

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Forgive me but in my opinion this is a wrong consideration.
The weight in the center of gravity of a rotating object in no way influences its rotation potential, that is the most irrelevant position for its performance.
The only appreciable difference by changing the weight in the center (and you can appreciate it with Side Effects), is the kickback you receive at the end of the throw given by the greater weight of the yoyo in general.
Remove a gram in the center is not like putting one in a peripheral position.

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Hi Fabrizio,

I know you know what you are talking about, but, I just tested what you said, using brass MarkMont side effects and aluminium ultralight side effects. I purposely chose the two sets of side effects that would have the greatest weight difference. The kickback was greater with the brass (as expected as the the MarkMont brass weigh 6.1g compared to the aluminium ultralight weighing 2.5g). The only other thing I can say is with the brass, the yoyo felt heavier (it should, it was 3.6g heavier). Maybe it was more ‘floaty’ with the ultralights due to the dfference in ratio of rim to center weight. So, definitely an effect on how the yoyo felt during play. However, I think my experiment confirms what you said, there is no difference in performance. I was able to do the same combo just as easily with either set of side effects installed. The yoyo is going to spin based on rim weight, which is unchanged regardless of what you do to center weight.

Please, if I am misinterpreting what you wrote, do not hesitate to correct me.

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Yes you have perfectly understood, I agree with you.
It is clear that by removing weight, I will feel the yoyo a little lighter and fluctuating, but it changes what I feel (and that in a few minutes I will get used to feeling) but it does not change the way the yoyo plays, which I mean as performance.

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But I’m not only considering the ability of the yoyo to rotate when I say that varying center weight can change how a yoyo plays. I suppose here I am not so interested in pure performance, in fact, but again, in how a yoyo plays (floaty or not, rapid deceleration of spin, overall feel, for example).

Sure, I’ve messed with side effects for a long time and they affect the feel of the yoyo in play significantly, no? Side effects tend to not go light enough for me and I wish they extended towards lighter weights, and this experiment with axles is an attempt to play around with that.

Ok, another example: I have a 54 that came with brass domes and at low RPM it struggled to return as well as I hoped. Putting in Al domes helped improve the 54’s performance at low RPM, and greatly improved the yoyo’s feel for my tastes. Did the yoyo spin better with Al domes versus brass domes? Not sure, but I enjoyed the handling at low RPMs much more with the Al domes.

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Ok, reading again, I think I understand your point of view.

Again, here when I mention how a yoyo plays, I don’t mean only performance.

This reminds me of previous debates about flat or centering bearings versus performance. Sure, both bearing types may perform the same with respect to overall spin time, but the difference in feel during play is an important consideration.

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I have not followed the discussions on the various profiles of the bearings but as far as I am concerned I realize that I have mounted one type in the yoyo rather than another only if I look at it, maybe I am not very sensitive myself, but in the bearings the profile for me only makes a difference so as not to generate friction (loss of spinning therefore) to the string against the wall, then actually, in certain types of tricks, where there are various lanyard passages in the gap, it is not a mystery that in a KK they tend to overlap, in a Central-Track, thanks to the flat central track they tend to stay side by side … but even here we still talk about “sex of angels”, in my opinion.
I have more or less the same consideration for Side Effects, or more generally for the experiments you are doing.
Of the SEs I recognize the great advantage (identical to that of the dice present in the Project) of avoiding throwing away a yoyo in case of stripping but as regards the “ability” or “the way” to play the yoyo, even if it changes it has never given me the sensation of such an important or significant variation; at least not like the one you would describe for 54 and certainly changing the weight in the center of gravity cannot make this happen:

This is also why I have some of SE … but not more than many.

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I repeat, maybe I am not very sensitive, however the rules of physics are not negligible in my view.

P.S. I would like to remind that among the first to experience the weight variations in the center of gravity was B! St, the Competizione had the hubs threaded externally and internally to accommodate many counterweights of different materials that were supplied in two sets with the yoyos … they are many years have passed and it doesn’t seem to have been followed in this aspect … usually features that generate significant I would like to remind you that among the first to experience the weight variations in the center of gravity was B!st, the Competizione had the hubs threaded externally and internally to accommodate many counterweights of different materials that were supplied in two sets with the yoyos …
They are many years have passed and it doesn’t seem to have been followed in this aspect … usually features that generate significant improvements… they have followed.

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Sorry me, I saw that you have already specified it in detail but I think it’s important to repeat it, I would not recommend using axles made of such a soft material like magnesium, tightening the cups well requires stripping the axis itself, not tightening them very hard, also due to of the blows that the cups receive in return phases with the hand, you risk that the same ones in play will loosen and turning in the same direction they unscrew very quickly making the yoyo open and jumping away …
It happened to me once and … it’s not a good experience!

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Yo. For the handful of you interested in this experiment, I’m here to bring it to its conclusion…

Short version:

Reducing axle weight by swapping out longer stock steel axles with shorter axles of different materials, like the Something doping axle made of Mg-alloy, can make a smaller yoyo feel more nimble, with the effect being subtle (Sparrow) or dramatic ('08 888). That said, the Mg-alloy axle feels “soft” when assembling the yoyo so I don’t trust its strength and thus don’t recommend it. In the future I might get some Ti-alloy axles to use instead. I think that on some yoyos it would be worth it, but your results may vary, as yoyo “feel” is important to me whereas if you are solely concerned with spin time this will likely not matter to you.

tl;dr:

I agree with @Palli that subbing shorter axles in 6061 alloy yoyos should be approached with caution due to the possibility of stripping threads. Proceed at your own risk if you want to try this. Also make sure the axle threading is compatible, for example if it is metric or not. That said, I used tiny 5mm YYR axles in an axle thread designed for a 10mm axle (the Sparrow) without problem. But then I’ve never stripped a yoyo, so far, because I’m really careful about this stuff.

Back when One Drop first came out with side effects (SE) I thought it was great to be able to try different weighting on the same yoyo with a simple part swap. Cool that it was mechanically strong, however the benefit of not stripping yoyos due to the SE design didn’t mean too much to me as this wasn’t a problem I encountered. I ended up with a little collection of SEs to try out different weights but generally found I liked the ultralights SE in everything. From there, I wished there was an even lighter-weight SE but I’m assuming there is a trade-off in the SE design, where the mechanical strength seems to require a minimum weight due to the SE seating and the axle used, with the axle being rather big in SEs, a 16mm steel M4 (feel free to correct me if the length is incorrect, I just pulled that from an old discussion).

Fast forward to today, when I’ve gotten tired of massive V-shaped yoyos and smaller organics have caught my fancy…

So the experiment was to reduce center weight in undersized yoyos where it might count the most.

For the Sparrow, which already uses a smaller axle and has a flat cup, swapping in a tiny steel axle or the Mg-alloy doping axle gave subtle results, and my conclusion is that the Sparrow feels just fine as is, stock.

For the '08 888, with its massive steel axle, the change to the smaller Mg-alloy was magic. After playing with my 888 with the Mg-alloy axle for a week or so, then changing back to the steel axle, I can say that the 888 felt so much better with the lightweight axle, it was more nimble and lively and more exciting to play. However, the mechanical strength of the Mg-alloy axle does not leave me with confidence. As @persson mentions above, Mg-alloy axles can themselves strip. So I fear that, long-term, playing the 888 with the Mg-alloy axle will result in it coming apart eventually and/or the axle breaking. So finally, I might eventually get a Ti-alloy axle for my 888 because I find the feel so much better with less center weight. Or… I just find another similar yoyo that has a flat cup and high rim weight like the 888 (any recommendations?).

Final thoughts… this experiment solidifies my interest in yoyos with flat cups, with clean lines in the design and the necessity of using smaller axles, the results are yoyos that I like more for both their look and feel. For undersized yoyos, the effect of lower center weight is more dramatic for their feel as compared to larger yoyos, where I think it could be worth it to swap in axles on undersized yoyos but not so much for normal or larger sized yoyos (≥54mm). The Sparrow is already more optimized for its weighting (for my tastes), but I think it’s worth it to tweak an 888, for example, by swapping in a smaller and lighter axle.

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I love your profile pic!! That’s my favorite episode, season one, episode 2

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