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Makes me wonder if there's a market for a set of go/no go gauges for various bottom brackets. Perhaps even make them deeper and then with an accurate bore and a ground shaft, see how well a pair of them line up.
If bottom brackets are as badly made as some of these, it would be nice to know before building up a frame.
If bottom brackets are as badly made as some of these, it would be nice to know before building up a frame.
In all the time you've been riding bikes how many do you personally know of where it's been a problem? I can't think of 1.
I can think of maybe high double figures on the internet but as a population sample that's like as not 0.
As a rider/owner I wouldn't buy your gauges for the same reason I've not got personal meteor or lighting strike insurance and any manufacturer should have one already
Not a fan of his approach (the zyklon B comment was uncalled for, and his fixation on MAB is cringy) but I like the engineering explanations and frame analysis.
The alignment on that BB is pretty shocking, and it should be correct. It shows a poor QA process from the manufacturer.
He’s a horrible little man and I won’t give him the time of day
Yep.
though saying that, he’s a classic example of survivor/selection bias with QC in the bike industry.
There is a bit to this, but it ultimately it shouldn't leave the factory, or should be rectified by the manufacturer (albeit I'm not sure they were given the chance in Kingdoms case)
The OPEN frame was an interesting example. Assuming that there isn't some lying going on with OPENS response, and regardless of how Hambini approached it, OPEN look foolish by saying 'we don't build to a standard for the BB' - i.e. we don't really care if your BB will perform correctly.
Having spoken to composites NDT specialists about assessing carbon frames in the past, I do query his NDT analysis - you need a benchmark to assess against.
Erm, he might be right about the frame and a good engineer but is he someone I would want to promote or give money to?
Not really based on why was reported by a female journalist.
https://ridewriterepeat.com/2020/06/05/six-bloopers-of-being-a-woman-in-the-cycling-industry/
Makes me wonder if there’s a market for a set of go/no go gauges for various bottom brackets. Perhaps even make them deeper and then with an accurate bore and a ground shaft, see how well a pair of them line up.
If bottom brackets are as badly made as some of these, it would be nice to know before building up a frame
If the frame is bad enough to cause a problem, I think you would notice it during installation...
I'd like to think I'd notice during building, but clearly some people haven't. And if it's true that some manufacturers are trying to claim a wider tolerance, perhaps a shop doing a lot of custom builds might like to know before getting too far into the build.
Having said that, I've only ever owned one bike (well, two frames of the same bike) with a pressfit carbon bottom bracket and the bottom bracket was about the only part that wasn't out of spec or poorly made.
But thats half the point. It could well have left the factory “bang on”
In this case the NDS was out as well - the thread bore isn't parallel with the shell (or not faced correctly on both sides). You can't cause that through damage.
It is a sample size of 1 for Kingdom, so they need right of response (although he said he contacted them weeks ago...?) and bad BBs will float towards Hambini for obvious reasons. However, the fact that he seems to have any sort business in selling BBs to repair the symptoms of this sort of problem indicates that poor QA is an issue in the bike industry.
If I buy a frame that has an X BB, I should be able to buy an X BB and it will fit as designed. If it doesn't (and presuming the BB isn't at fault) then the frame is defective and the manufacturer should repair, replace or refund.
I’d like to think I’d notice during building, but clearly some people haven’t. And if it’s true that some manufacturers are trying to claim a wider tolerance, perhaps a shop doing a lot of custom builds might like to know before getting too far into the build.
To be fair thats true. I think a shop should have to think about something like this otherwise it's harder to identify faults. Misalignment isn't very easy to do though.
If a product requires home QA it identifies a serious issue across the industry.
One slightly off frame does not mean there is a problem with this model, or brand, or factory, or industry. Don’t extrapolate out like that, especially based on the rants of someone after attention to sell you something.
One slightly off frame does not mean there is a problem with this model, or brand, or factory, or brand, or industry. Don’t extrapolate out like that, especially based on the rants of someone after attention to sell you something.
Yup.. as I alluded to above, frames with bad BBs will gravitate towards Hambini so it becomes an echo chamber.
The Kingdom example is just that, a single example and we don't know the back story of the frame (it could have been a 'seconds' frame, or a fake for all we know).
He knows his engineering onions and shows up poor QC on expensive frames. I’ve no issues with that.
Sweary and annoying yes. Dealt with way more annoying folks again no issue.
Part of the draw I guess would he get same amount of coverage if he was a monotone boring engineer?
Carry on Hambini
If a product requires home QA it identifies a serious issue across the industry.
I agree with Kelvin on this one. It identifies that certain frames/manufacturers have lower standards than others. It tells you nothing about how the industry is overall.
I'd personally have be sceptical about taking too much away from a guy that goes out of his way to convince you a bent line is straight - I mean whats that all about? Its clearly bent (You can see it is, pause the video and test this for yourself with a straight edge if you're still unsure, it's not straight). Weird.
If a product requires home QA it identifies a serious issue across the industry.
I said this on another Hambini thread. My guess is that the large-scale manufacturers (Giant, Trek, Spesh/Merida, etc.) will have fairly consistent QC. They turn out frames by the tens of thousands so they can afford to spend millions on factory equipment to keep everything consistent. They can also scrap frames because they will have much lower labour costs than niche manufacturers. When you have a small manufacturer building custom frames, the QC will probably be much more variable. Labour costs will be a huge proportion of their expenses, so there will always be a temptation to let stuff through if you think you can get away with it.
I agree with Kelvin on this one. It identifies that certain frames/manufacturers have lower standards than others. It tells you nothing about how the industry is overall.
And I'd agree with that 🙂 I was talking cack.
In hindsight, what I should have said was that 'if it gets to the point where poor factory QA means that an industries products require the consumer to complete home QA, then there is an issue in that industry'.
I/we don't know if there is and I doubt there is evidence to support that. I suspect most people wouldn't realise if their BB failing after a few months (as a random example) is frame related, BB related, maintenance related or installation related...
I said this on another Hambini thread. My guess is that the large-scale manufacturers (Giant, Trek, Spesh/Merida, etc.) will have fairly consistent QC. They turn out frames by the tens of thousands so they can afford to spend millions on factory equipment to keep everything consistent. They can also scrap frames because they will have much lower labour costs than niche manufacturers. When you have a small manufacturer building custom frames, the QC will probably be much more variable. Labour costs will be a huge proportion of their expenses, so there will always be a temptation to let stuff through if you think you can get away with it.
It's more important for the niche manufacturers as well. They are selling a usually more expensive version of a product and quality becomes a huge part of their USP.
As a more general aside, I worry about the idea of giving allowances for problem frames making it out to the public. A misalignment issue is annoying, a poor weld or other structural concern is a different ballgame...
Fair enough. To be honest if you fit a 30mm BB in a BSA frame you should expect it to fail within a year. There are no good ones as far as I can tell. We stopped selling 30mm axled cranks for that reason. Even the most expensive ones fail quickly relative to their 24mm equivalents. 30mm is a step too far for BSA BBs. SRAM wisely dropped a mm from theirs to make it work, and of course got panned by many keyboard warriors for being awkward despite the fact that it was completely (and obviously to be fair) necessary to make a single, large bore axle work on all platforms.
There is for sure a QC issue in the far east - they focus more on delivery of the quantity than the quality. Left unchecked they will deliver you X-hundred frames on the date you wanted them whether they're all good or not. If you take your QC seriously you need to instigate a second level of QC away from the factory, or embed someone there. Nowadays, we bring all the frames into the UK, disassemble then reassemble each one and only after its been checked they get built or shipped out again. And we use 2 of the 'best' factories.
Yeah, a second (or even third) line of QC is wise… but no one should be taking away from this that Kingdom don’t do the same. This is just one frame.
One swallow does not a summer make.
Yeah, a second (or even third) line of QC is wise… but no one should be taking away from this that Kingdom don’t do the same. This is just one frame.
One swallow does not a summer make.
🙂
Funnily enough I quite like the Kingdom frames as frames go, although can't say im sold on LT hardtails in general. I have found it hard to balance travel Vs weight Vs comfort - I always felt like I was under or overbiked for the situation
Is 9001 (or variants) widely used in the bike industry? I work in the aerospace industry and was (less so in the last year) heavily involved in the business management system, which was based on 9001. It's great having a QC process, but unless you are holding your own internal processes to account it quite quickly becomes wallpaper (learnt this the hard way!).
Is 9001 (or variants) widely used in the bike industry? I work in the aerospace industry and was (less so in the last year) heavily involved in the business management system, which was based on 9001.
This is the same industry that made an airliner programmed to fly itself into the ground?
Neverminding the BB for a moment, and the sweary man. Remember reading somewhere that visual appearance of a Ti weld isn't a good indicator of weld integrity, however- not sure I could part with money for something that's as messily welded as that - not when some of the Ti specialists, Moots, Eriksen, etc, show how neat Ti welding can be... or is that neatness just artful showboating and not necessary?
He’s an acquired taste
He's at the very least a misogynist who's encouraged others to violence and is apparently happy to use Holocaust imagery, that's not a "taste" anyone should be in a hurry to acquire quite frankly.
And let's not forget the whole point of his You Tube channel is to drive footfall to his own shop. His whole "shtick" is basically "Oh look, low cost high volume manufacturers sometimes don't have have great QC". That shouldn't come as a massive surprise to any fully functioning adult and that fact that he keeps repeating it, only serves to re-enforce the fact that some folk are clearly hard of thinking. You can have your own opinion on whether slagging of other manufacturers products in order to promote your own is a viable long term strategy; personally I think it's pretty low drawer, and will likely invariably end with a "hoist by your own petard moment" if one of his own products fails.
Given it's a 2nd hand frame with unknown provenance only serves to re-enforce his douche-bag status to my mind.
will likely invariably end with a “hoist by your own petard moment” if one of his own products fails.
I always assumed he was the product, kinda like Donald Trump.
This is the same industry that made an airliner programmed to fly itself into the ground?
Same industry, completely unrelated process.
The story behind that is quite eye opening. BBC did a good article on the history of it. Reassuring (it wasn't a failure method that could impact other planes) and worrying (how the hell was it allowed) in equal measure.
At best it was incompetence on behalf of the manufacturer and the authority, but some of the decisions make you wonder what was actually going on
Is 9001 (or variants) widely used in the bike industry?
Yes, and I've seen really sloppy QC from factories that are ISO9001 certified. One of the problems is there has to be a check for something in the first place, with so many changes to spec and design and factory efficiency being based on not changing the entire QC process every time a different product goes down the line, or no more than you really need to, that's where errors come in.
It’s great having a QC process, but unless you are holding your own internal processes to account it quite quickly becomes wallpaper (learnt this the hard way!).
Exactly this too. A tick in a box doesn't always mean it was actually checked.
My guess is that the large-scale manufacturers (Giant, Trek, Spesh/Merida, etc.) will have fairly consistent QC. They turn out frames by the tens of thousands so they can afford to spend millions on factory equipment to keep everything consistent. They can also scrap frames because they will have much lower labour costs than niche manufacturers. When you have a small manufacturer building custom frames, the QC will probably be much more variable. Labour costs will be a huge proportion of their expenses, so there will always be a temptation to let stuff through if you think you can get away with it.
IME it doesn't really work like this. The bigger factories are generally big because they reliably produce on time at a workable price and quality level. Smaller factories can appeal to brands who can charge a premium, the brand pays the factory a premium them because they're good at making things accurately, being adaptable with smaller MOQs etc. The good factories of any size pay better to keep staff as that helps efficiency which helps minimise overheads. And as Ben said, it's the imbedded QC resources or importance of the business relationship that keeps things in line more than anything else.
IME it doesn’t really work like this.
The bigger point though was that it's not really a problem "across the industry", just that some manufacturers (might) have QC problems. I've never owned a custom frame, but the mass produced frames I've had have all been fine.
Agreed, I wouldn't say it's a whole-industry problem. I think if things generally slowed down a bit and were less price driven we might see fewer problems but there are good factories and brands out there who always have done and will do things well, and they get a deserved rep for it. I think it's worth supporting them.
Poor QC is one thing but surely if these brands were prepared to hold their hands up and offer customers what theyve paid for on the warranty hambini wouldnt have much to rant about.
benpinnick has it right. you need people at the other end. targets will be met even if some shite needs sent to get it done.
Having a good laugh at the Kingdom apologists here "don't expect aerospace grade engineering"!
In fairness, he’s a bellend when critiquing other manufacturers too.
How many of us actually take time to measure a press fit BB shell (for example) on a new bike though - size, ovality and alignment?
Realistically never, just slap the BB in with a bit of grease and never think about it again until it starts creaking.
Interesting video above, and quite refreshing to see a normal guy talking engineering.
Not too geeky and just normal without getting all shouty and sweary like the child who made the bottom bracket.
His talk on his new mtb was good too, will watch his vids more me thinks.
edit. Forgot to ask the main question.
Am I being a bit daft but, how does the bottom bracket go into the frame? Normally one end comes off so it can be pushed through but the talk of it being one piece etc seems to negate that.
edit edit 😀
Presumably it pushes through completely. Makes sense... doh.
Thanks for the vid Paton...reassuring as I have one of these going into my build, albeit the non-racing version.
Figured it may prove cheaper in the long run than swapping out two piece units should I get any alignment/creaking issues.
nickc
His whole “shtick” is basically “Oh look, low cost high volume manufacturers sometimes don’t have have great QC”. That shouldn’t come as a massive surprise to any fully functioning adult and that fact that he keeps repeating it, only serves to re-enforce the fact that some folk are clearly hard of thinking. You can have your own opinion on whether slagging of other manufacturers products in order to promote your own is a viable long term strategy; personally I think it’s pretty low drawer, and will likely invariably end with a “hoist by your own petard moment” if one of his own products fails.Given it’s a 2nd hand frame with unknown provenance only serves to re-enforce his douche-bag status to my mind.
'high volume low cost' ... they're £1000+ carbon fibre (and in this case titanium) bikes, not £69 BSOs from Argos.
Apparently I must be hard of thinking because it was surprising to me that bikes at that price point would be leaving the factory with a crank that cannot spin freely. It's piss poor and I'm glad he exposes it.
As for his humour, not my thing, but then again not really any worse than Frankie Boyle (e.g. 'i bet your pussy's seen more action than helmand province', rape joke about victoria pendleton not being able to lift him off of her, whatever it was he said about Jordan's disabled kid etc) that a lot of people are apparently fine with.
Apparently I must be hard of thinking because it was surprising to me that bikes at that price point would be leaving the factory with a crank that cannot spin freely. It’s piss poor and I’m glad he exposes it.
But, it didn't leave the factory that way. It's a second hand frame that could well suffer a bent ISG mount that could cause that exact problem, AND its a 30mm axle BSA BB being fitted years later, a style of product which are generally notorious for being draggy irrespective of the frame.
But, it didn’t leave the factory that way.
To be pedantic, I'm not sure that's ever been established?
benpinnick
But, it didn’t leave the factory that way. It’s a second hand frame that could well suffer a bent ISG mount that could cause that exact problem, AND its a 30mm axle BSA BB being fitted years later, a style of product which are generally notorious for being draggy irrespective of the frame.
Ben, I was talking about the channel as a whole in response to nickc's comment that these are 'high volume low cost' frames. Time and time again, even on expensive gear we see BBs that are oval, not aligned, undersized etc. It's utter crap and I'm glad he exposes it.
A correctly aligned and sized BB shell should not be too much to ask on any bike more expensive than a BSO really. Let alone on a £2000+ bike.
If you think that's the cause on this specific frame, why don't you post it in the comments on his video. I would at least watch it first though.
A correctly aligned and sized BB shell should not be too much to ask on any bike
People would only bitch about yet another standard 😉
dangeourbrain
People would only bitch about yet another standard 😉
😀
If you think that’s the cause on this specific frame, why don’t you post it in the comments on his video. I would at least watch it first though.
I have watched it. I don't know what the cause is, but I certainly learned nothing about what it might be watching the video though, and that was my point.
I do agree there's lots of crap out there, but if someone thinks paying 2/3/4 times the price for something equivalent will get you better quality then you've missed the 'they all get made in the same factories' comments that have been a constant in the bottom half of the internet for a long time. They do, and you should not expect that price has much correlation to quality of output. There's a minimum spend to get the better factories, after than quality comes down to design and the willingness of the manufacturer to manage it. Neither have a massive influence on the price unless you go to the extreme end of the quality control spectrum, but then you'd know that you were there, as they'd tell you about all the awesome things that they do.
... By 'you' I dont mean you specifically retro83, its a general you. Just to be clear 😉
have watched it. I don’t know what the cause is, but I certainly learned nothing about what it might be watching the video though, and that was my point.
That must've taken some effort on your part.
I can see that you might continue to disagree with the theory he puts forward as to the cause, but it seems to me that he explained that view quite clearly and at length. Much more likely you understand it very well and disagree with it, no?
‘high volume low cost’ … they’re £1000+ carbon fibre (and in this case titanium) bikes, not £69 BSOs from Argos.
Apologies, my rant wasn't clear, I meant low cost in terms of manufacture not retail.
I can see that you might continue to disagree with the theory he puts forward as to the cause, but it seems to me that he explained that view quite clearly and at length. Much more likely you understand it very well and disagree with it, no?
No, I don't necessarily disagree with the theory as to the cause - its as likely it was made that way as any other explanation. But that boils down to 'They welded it up wonky and didn't face it off afterwards'. Getting to that conclusion as a possible didn't require much thought and because there's no concrete evidence that its not been bent out of shape we can't learn much from that.
I lasted 5 secs with him after he dissed all but threadless BBs
I do agree there’s lots of crap out there, but if someone thinks paying 2/3/4 times the price for something equivalent will get you better quality then you’ve missed the ‘they all get made in the same factories’ comments that have been a constant
Interesting comment from someone that knows more than most (nearly all on here to be frank). I got a lot of "oh but Hambini doesn't like it" comments on my post about my new Open Up the other day. I literally couldn't care about anyone's opinion besides my own on inanimate objects.
In my view, Open frames are massively overpriced for units from the same factory as frames half the price, but I got a frame I have an affinity to and want to ride and really, that's the only difference. I think the nuances between frames are so small that 9 times out of 10 it's a placebo anyway (new bike effect etc).
If you can afford something expensive and like it, great. If you can't, don't worry, you're missing nothing.
If you have a frame that works fine and you like, then that is brilliant. It's worth what it's worth to you.
For me, the big takeaway (based on what we have been told at face value) from the Hambini / Open debate wasn't the quality of a single frame, but Opens response to the criticism.
Hambinis approach is what it is, but to come back and defend yourself by saying that they don't build to a given standard and going legal immediately is quite bizarre. As a customer it would not fill me with any faith in them if I ever had an issue with their products.
If they had responded by saying "we haven't seen this frame, we take things like this seriously, we are going to investigate this frame and the process by how it was released to the public" and then share the results of that process and their response, it puts them above reproach. Especially as they should be doing that anyway.
I lasted 5 secs with him after he dissed all but threadless BBs
Cycling industry is the only one I can think of that threads a bearing carrier into another part. Everywhere else is pressed in, with a properly designed (tolerance, sealing, good engineering standard) and then properly manufactured. Press fit would work, but because we have shonkily designed and then shonkily made stuff, it doesn't last, so having something that can easily serviced is less impact/annoyance to the end user.
I'd imagine the cost/complexity of facing that Kingdom BB resulted in it not being done. Design for Manufacture lacking somewhat.
Afternoon.
Sorry for bringing up and other thread at risk of upsetting the frothers.
The original Kingdom/Hambini video has been taken down now, I imagine for obvious reasons, but I wanted to put a follow up to my own experiences with this.
I have a kingdom vendetta - the mtb frame in the original video. Its a brilliant frame, except that it eats bottom brackets. Since it's my winter bike in the main, I thought little of this, but Hambini's comments had me thinking I ought to at least check the BB facing on mine.
I eventually got around to it last week after being on the FS all summer.
This is the result of BB facing the drive side.
The lip you can see is the outside edge of the facing tool. The drive side BB was out approaching 0.5mm. I've had to chase the BB shell down to 72.5mm to get it lush around the diameter.
This is the same BB prior to facing.
It's close up so the finish can be seen, because it looks like its been ground back flush. It's a totally different surface finish to the facing tool. Interestingly, the NDS side didn't need facing in the slightest.
I think the act of welding on the ISCG plate distorts the end of the pre-faced BB tube and then its re-finished. In my case, and possibly in the now unavailable video, its not been re-finished adequately.
I suppose the moral of my story is that you should still get these things checked out instead of assuming.
I'm of the opinion that facing a threaded BB will never correct anything. I'm happy to be convinced otherwise.
I've asked this before, but never got an answer that sits right with me. Let's assume the BB shell starts as a straight uniform cylinder. Then cut a two threads into it one from each end, or send the cutter all the way through, I don't know. Once you screw in your BB cups, the only thing they can align them will be that thread, no?. Once it's screwed up snug, if the raw shell and the threads are in good alignment, and the BB threads are also well placed, then the face of the BB cup will be snug to the face of the BB shell. If either thread is misaligned, either you have a gappy shell to cup join, or you're deforming something, which my instinct says can't be good for running bearing smoothly. BB facing doesn't alter the alignment of threads anywhere, so even if you face a misaligned frame you would still end up with a bearing running in the wrong plane. So why worry about facing?
^ But if you screw a nut onto a bolt, you can wiggle the nut though because the threads don't exactly match.
That said, we 'had' to face BB shells when external BB's came out, and there were no end of debates regarding this BITD. Nowadays it seems that it's hardly ever done. Shimano use plastic spacers because the compress slightly to remedy slight imperfections. 0.5mm as above is a pretty big error though.
Facing is usually done in conjunction with chasing the threads so the threads get re cut cocentric to each other.
As for the unfaced end, you've probably see how badly people can hammer a headset in cock eyed. Same with unfaced headtubes, you can hammer a headset in and it will sit perfectly flush with a very poorly aligned frame to the point it won't stay adjusted correctly.
I think it will depend on the manufacturing sequence. My assumption was that the BB threads were cut after all the welding was finished, then facing was done as the final step. I don't understand why anyone would cut the threads before welding. As long as you cut the threads after the frame is welded, they should be perfectly aligned because they'll be cut simultaneously on the same jig. The only way I can see things getting misaligned is by trying to save money by machining the BB shell before the frame is welded.
Sure the 0.5mm on Scienceofficer's frame is a big chunk. The plane of the face is now aligned 0.85 degrees different to before. Now screw in the cup, does the bearing now sit 0.85deg different too, and if it does, how?
screw in the cup, does the bearing now sit 0.85deg different too, and if it does, how?
Aluminium is pliable and you underestimate the force you can get from a ~1.37"x24tpi thread that and quite fine. Deforming the 'cup' part will be no problem.
Remember you can snap an M6 bolt with an Allen key!
My understanding is like @walleater's, threads (V-profile threads anyhow) do not lock the two parts in perfect alignment, they are designed for the two parts to be able to wiggle about relative to each other and "find" comfortable relative positions that spread the load out more evenly than would be the case if the threads were a perfect fit. Which is good where a strong join is what is needed, rather than perfect alignment of the two parts.
So with non-parallel facings, tightening the cups up will result in some displacement from the ideal alignment (assuming the two ends of the bb tube are threaded co-axially in the first place), as well as causing some distortion of the cup (this could be a greater effect than the displacement of the threads). What the amount of misalignment and distortion would be, and whether it would be significant, is a matter of observation, but @Scienceofficer's experience suggests that the amount of mis-facing in their frame is sufficient to have noticeable effects. Though we await to hear their further experiences of wear with the newly-faced BB shell.
It may also make a difference whether you have Shimano style bearings with the plastic top-hats inside, or what everyone else does, which is have the crank axle sitting directly in the inner bearing race.
Aluminium is pliable and you underestimate the force you can get from a ~1.37″x24tpi thread that and quite fine. Deforming the ‘cup’ part will be no problem.
If you can get past his internet caricature, Hambini makes specific reference to this.
The gist is that with a 30mm (or DUB) in a BSA BB shell, theres insufficient space for a decent sized bearing and/or the bearing cup itself. The end result is that without plumb BB shell faces, the BB cup deforms and over-pressures the bearing which can run tight, feel rough and wear quickly. Either that, or the bearing cup flexes under cyclic pedalling load and causes fretting on the crank axles (especially soft alu axles).
This is kind of all solved by having a smaller axle like shimano, which leaves more space for bigger bearings and thicker bearing cups or a bigger BB shell like T47. To give more space for the whole BB30 arrangement.
The jury is rather obviously out on BB wear right now. Observations are that it all slid together rather more nicely without force and it does seen to spin better. This could be confirmation bias though. The truth will be measured by BB lifespan. Since I keep a maintenance schedule, it should be easy to measure any differences in durability.
Hope it works out, Scienceofficer. Looking back, I think we peaked with Octalink!
In the majority of fabricated frames, threads are cut before welding.
Machines to cut the threads after fabrication do exist - when Chas Roberts shut down there was a list of tooling for sale that included an ancient and rather scary looking threading machine. You would really struggle to cut a bb thread from scratch into a plain shell with the standard hand taps. And if you manage it, it is unlikely to be properly aligned.
There is usually enough slack in the bb threads that an unfaced / misaligned end face will skew the cup when tightened up (maybe not completely but enough to eat bearings).
Any post weld thread tapping is to remove any local distortion / gunk in the threads. The threads are not being recut to be perpendicular to the newly faced end. But it does add a bit more slack to let the faces control the final alignment.
If you are clumsy with heat, bb shells can be distorted (slightly bent like a banana - they pull to the heat and one side doesn't get heated). This leaves both ends out of parallel and both threads out of line. If not too severe, facing the ends and tapping out the threads allows enough slack for everything to align (ish).
Regardless, lots of bbs die in the UK due to water killing the bearings - either from inside the frame or tracking between the bearing and axle by capillary action.
I still prefer Shimano UNxx Square taper cartridge bbs as they solve all these alignment and sealing issues in a £20 unit. In my 32 years of mtbing they have been the single biggest advance in reliability 🙂
I still prefer Shimano UNxx Square taper cartridge bbs as they solve all these alignment and sealing issues in a £20 unit. In my 32 years of mtbing they have been the single biggest advance in reliability 🙂
The BBs were fine. It was the stretched taper in the lh crank arms that was the issue 😁