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Spoke holes not exactly radially centered to hub flange?

Old 08-17-19, 08:25 AM
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tomtomtom123
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Spoke holes not exactly radially centered to hub flange?

I received a Novatec front hub and am checking the dimensions. I noticed that the spoke holes aren't exactly radially centered to the hub flange. Some holes are around -0.25mm closer and some are +0.25mm further away from the center. Will this be acceptable, and are there any real practical problems with having holes with this small amount of misalignment?

I saw an article from a bike site of a Novatec factory tour. It seems they cold press raw bars into the general shape of the hub, then a CNC lathe cuts the shape down to it's final and more precise form. The article did not show how they drilled the holes, but if the holes were drilled by the same CNC lathe while the hub was still mounted inside the machine, then the holes should be fairly accurately centered. However, if they took the hub out of the lathe machine and put it into a nomral x-y-z cnc milling machine, I would expect a tolerance of +/- 0.1mm due to reclamping of the hub into a different jig. But a larger tolerance of +/- 0.25mm seems to show a less precise workflow.


Also, the design of the end caps leaves a large gap between the cap and the hub body. It invites large particles to fall into the gap.

Also, the hub body seems to have been designed for the cartridge bearings to be flush against the outside surface of the hub. However, the bearing on one side is +0.15mm outside the hub body, while the other bearing is -0.15mm recessed into the hub. this doesn't make much of a practical difference, since spoke tension will easily fix a small amount of wheel dishing, but it shows what kind of machining precision they're using. You can almost see the in the photo below, the bearing coming out past the surface of the hub body. This makes the gap to the end cap +0.3mm larger than the gap at the other side of the hub.
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Old 08-17-19, 08:55 AM
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Originally Posted by tomtomtom123 View Post
I received a Novatec front hub and am checking the dimensions. I noticed that the spoke holes aren't exactly radially centered to the hub flange. Some holes are around -0.25mm closer and some are +0.25mm further away from the center. Will this be acceptable, and are there any real practical problems with having holes with this small amount of misalignment?
The dimension you're measuring isn't really all that important. What matters (but not a huge amount in practice) is that the holes are the same distance from the center of the axle. The OD of the flange isn't an issue when lacing a wheel unless it is significant amount.

Better QC would have probably scrapped this hub, but if the spoke holes are all located along a circle that is concentric to the axle, all is good.

As to the bearing being slightly proud of the hub, that could probably be addressed with a socket that contacts only the outer race and some slight tapping with a ball peen hammer. There is likely a spacer between the bearing inner races that positions the bearings. It does seem like the measurements show that the bearings should be flush to the hub, but that should be a fairly simple task. This has to be done when replacing cartridge wheel bearings anyway, so it isn't a serious problem. Again, better QC would have had the bearing fully seated in the hub. Unless the bearing seat isn't bored deep enough to allow that, in which case this would be a problem.
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Old 08-17-19, 09:46 AM
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I can't measure the distance between the spoke holes and the axle/bearings, or at least I don't know how to do it with calipers. But I am assuming that if the CNC lathe cut the bore hole for the bearings to go into, and did a final pass over the flange in the same cutting session, then the flange should be centered to the axle. That's why I am assuming that because the spoke holes aren't centered to the flange, that the spoke holes are also not centered to the axle. But I could be mistaken. The only way I know of to confirm whether the holes are centered to the axle, is to take out the bearings so that I can get the calipers in there to take a measurement. But if I knock out the bearings now, I'd have to go and buy some replacements.

Assuming that the spoke holes are +/- 0.25mm offset from the axle, what problems would there be? The spoke tension should true the wheel. But I assume the tensions will be different from one quadrant to another due to slightly different spoke angles and lengths.

I think the bearings are already seated all the way into the bore holes. One side is probably not bored as deep as the other. I suspect this because all the other axial dimensions of the end caps, axle, and shoulders all have 0.15 in them, which is probably the lateral tolerance that the factory uses. But I'll try making bearing presses/drifts to see if I can press the bearings any further in.

I also I have a different OEM hub of a similar design that's probably all made in the same factory, and that hub also has one bearing 0.15mm further in and the other bearing 0.15mm further out. I took the bearings out and put new ones in, and they still had the same offset. Although both were inset either 1.4mm or 1.7mm in past the face of the hub body, so I don't think it made a practical difference.
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Old 08-17-19, 10:23 AM
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When you build the wheel it will be centered on the axle not on the spoke holes. I would be more concerned about the bearing not seating.
I don't think that you expect high quality at their price point.
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Old 08-17-19, 11:21 AM
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First off you are using a digital caliper which are notorius for skipping.

Tighten the friction knob...zero...slide...measure.

I bet you'll get better numbers.

I use analog calipers for all my measurements.

Anyway...as already mentioned you're building to multiple centerlines...you might get a slight variation in where spoke ends end up in the nipples, but not much else.

Also, a reminder that Novatec, no matter how good or high tech they look - they are budget cartridge bearing hubs - a mid range product.

If you want perfection, Phil Wood, Paul, Chris King...etc.

=8-)
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Old 08-17-19, 03:15 PM
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I know that the digital caliper that I use can't be trusted for the 0.0X mm digit, but it is fairly accurate to the nearest 0.Xmm, within +/- 0.05mm. I know that it can sometimes skip so I always double or triple check the zero and remeasure again.

So I'm pretty sure that the maximum total variation in the spoke hole centering to the flange is somewhere around 0.25mm +/- 0.05mm. I'm building a 406 20" wheel, and small wheels seem to be more sensitive to minor spoke tension adjustments due to the shorter spoke lengths and small diameter. (edit: I did a rough diagonal measurement between the holes and the axle and it seems that the holes are not centered to the axle, offset a similar amount as to the flange).

Yes, the price for the Novatec hub was very cheap, but there isn't many other choices readily available for 74mm hubs with the spoke counts that match the rims that are available locally. The only alternative hubs I've found locally are either unknown no-name hubs, or the loose ball OEM Quando front hubs that are recently found on some current Dahon and Tern wheels. I was thinking about going with the loose ball hub, but recently I had trouble finding a replacement cone for a pitted one in the rear OEM hub on my dahon bike, so I'd probably have to buy 2 of the Quando hubs, and use one as a spare if I need to replace the cone. So I thought I'd stay with cartridge bearings for the front.

The only worry I have is the possibility that the cheap Novatec hubs on Aliexpress being rejected units, for being outside of tolerance.

The design of the end caps would have been better if the bearings were set in around 1.5mm mm past the face of the hub body, and the caps went inside by 1.0mm. Because most dust particles would hit the bearing radially and against the direction of travel, instead of laterally. The huge gap on the Novatec hub between the cap and the body lets in everything, except for dust that is flying sideways, when the bike is at a standstill..

Last edited by tomtomtom123; 08-17-19 at 03:59 PM.
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Old 08-17-19, 06:22 PM
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Originally Posted by tomtomtom123 View Post
I can't measure the distance between the spoke holes and the axle/bearings, or at least I don't know how to do it with calipers......
You really don't need to. I just slapped this together.
LOOK for differences re: "the pointer" in relation to the outside of the hole.
IF it's anything meaningful, it'll be VERY obvious.

There are 2.2 turns per mm, so .25mm is .55 turns.
Ask a wheelbuilder if they keep track that close....
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Old 08-19-19, 11:17 AM
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This reminds me of a wheel on a bike I was lent by a shop I used to work at. It had Novatec hubs front and rear, and while the wheels were straight and generally spun smoothly, the rear hub seemed designed to leave the job of keeping the freehub in line with the hub body to a 10mm diameter aluminum axle. I experienced skipping and popping and grinding from the rear wheel as I rode, and the wheels of other cyclists showed major wear in the ratchet mechanism after a year or so of use.

This may not be 100% relevant to the OP's story, but OP's story certainly reinforces my belief that Novatec hubs are not very good.
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Old 08-19-19, 05:25 PM
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Novatec's are fine for light, low torque riders or riders who stay 95% in saddle.

But once Mr. Beasty is standing on the pedals and hammering..Novatec's lightweight mechanicals will take a beating.

Chosen's will get chewed up as well.

=8-
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Old 08-19-19, 05:43 PM
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There is only one thing I wold worry about - is there enough material around the spoke holes at the biggest distance from center.? Any chance of a flange breaking? This is very uncommon in low flange hubs.

There is another matter which could affect the wheel build in two ways. 1) the lacing and first tightening and truing will take longer because of the spoke length discrepancy. Add 30 minutes to wheel build time. And 2) the most extreme spoke holes might lead to the spokes not being long enough and potentially popping heads or being too long and bottoming ou on the threads. If the spokes are picked to extend just past the spoke head, the builder will have a coulple of millimeters of grace in both directions.

Once a good wheel is built, no one, owner, rider or bike is ever going to know or care about the asymmetry of that hub.

Ben
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Old 08-30-19, 10:07 AM
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I extracted the bearings to measure the internal dimensions of the bearing shoulders.

The axle shoulders are 38.15mm (+/-0.05) wide, while the hub bore hole bearing surface is around 37.82mm (+/-0.1). I have to measure the hole indirectly because the hub body tapers in the center, so this measurement isn't precise. But at least the difference between the body and and the axle is around 0.33mm (+/-0.15).
(I later measured this more precisely to around 0.40 to 0.55mm)

Is it better to have this difference in width as close to zero as possible? How is this normally designed by other manufacturers?
Or is it better to have the hub slightly narrower, or the axle slightly narrower?
I assume axle slightly narrower by less than 0.05mm is better, so that outer bearing trace will contact the hub sides, and the inner trace will add a little bit of preload when clamped into the dropout.
( I later measured the axial play of the traces at about 0.02mm, so I could potentially add a preload of about 0.04mm)

With the way it is now with this novatec hub, the inner trace will be clamped tightly against the axle shoulders, but there is a gap between the bearings and the inside surfaces of the hub. Wouldn't the bearings slip around?

I'm thinking of adding shim washers to fill the gap. I can find some din 988 19x26mm in 0.1, 0.2, 0.3mm thicknesses.
The lathe that i have access to has a lot of backlash so I'm not confident that I'll be able to cut the shoulder narrower.

I created another post comparing the exterior dimensions of other 74mm hubs for folding bikes here:
https://www.bikeforums.net/folding-b...on-others.html

Also, one side of the axle has an interference fit with one bearing, while the other side of the axle has an "easy" fit that slights in without much interference. The bearings are TTN chinese branded, and strangely the widths are 8.05mm instead of 8.0mm.

During extraction, a lot of metal shavings came out, and I'm not sure whether it came from the hub surface, axle, or residual waste from machining.(shavings came from threads on the bolt I used for extraction) The inner surface was dry without grease, and very dirty.




Last edited by tomtomtom123; 08-30-19 at 06:17 PM.
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Old 09-01-19, 03:26 PM
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I measured the difference in shoulder width to around 0.4-0.5mm. I'm going to fill the gap with washers. But I'm wondering if I should simply use flat washers, or consider wave washers?

This PDF shows wavy washers on both sides of a Philwood front hub. But it's unknown to me how much force they're supposed to exert, which is related to how much the washers are compressed.
https://www.bbinstitute.com/dl/dx_demo_chapter_13.pdf

This blog shows the washer:
https://softsolder.com/2014/04/17/re...-hub-bearings/

With the gap of only 0.4-0.5mm, I could insert 1 wavy washer on each side, and the pair would add around 10kg of axial load at full compression. I don't know if preload improves anything or creates problems.
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