Square Taper Cranks

[northeastcyclist]

Trying to plan how to make an internal square tapered hole to accept a Shimano BB and can't seem to find how those internal square tapered holes are comercially made. How on earth do they make those internal square tapered holes on cranksets? Does anyone know?

[Jamesh]

Usually they are drop forged the better ones or cast forged the lesser ones iirc.

How's the project going?

Cheers James

[rogerzilla]

A programmed milling machine, I imagine. It's not easy, as evidenced by the poor tolerances on a lot of them; you can get different chainlines with different specimens of the same model, or with supposedly identical-length BBs.

[531colin]

Trying to plan how to make an internal square tapered hole to accept a Shimano BB and can't seem to find how those internal square tapered holes are comercially made. How on earth do they make those internal square tapered holes on cranksets? Does anyone know?

Do you have to make one from scratch, or can you re-purpose an existing crank?

[hamster]

I have a piece of steel from a tandem drive conversion with a square taper and threaded outer, let me know by PM if this helps you.

[northeastcyclist]

Thanks for the help guys. I thought you could just turn one on a lathe with a square broach and file down the sides, but the accuracy would be terrible. But I never even considered drop forging. Now that you've mentioned it, it does seem quite obvious.

The Project is going well, thank you James! The part I'm having to make is a monstrosity of gemeotry itself, even without the square tapered hole. It fits to a Shimano BBUN55 and a Lever fits inside that cylinder to drive a freewheel:

Think this would have to be 3D printed, only wondered if there was a way to achieve a higher accuracy hole by some magical machining means, since the method suitable to make this is only accurate to within +/- 0.1mm.

I've spent a good few hours thying to find the answer to this today. I don't know why I don't just come straight here. You guys are alot more helpful than the Internet!

Thank you very much for your help and offers guys!

[slowster]

Would it be easier/more practical for your particular purposes to design and manufacture the chainset with a cottered crank fitting instead of square taper?

You can still buy bottom brackets for cottered cranks and cotter pins.

https://www.sjscycles.co.uk/cottered-traditional-axle/

How Raleigh used to make them - 10mins 5 secs in:

[KTHSullivan]

It can be done but it depends if one has access to a serious engineering workshop, it would however be quite a convoluted and time consuming process.

You would need a precision rotary table (or a dividing head) mounted on an x-y axis table, a set of broaches, slip gauges, sine bar and a broach press.

Also the component would have to be manufactured on an initial basis with a sacrificial stub for holding purposes that would be machined away after the taper was manufactured.

Probably quicker to use a file.

K

[531colin]

https://spacycles.co.uk/m8b0s109p2188/S ... e-Chainset
start with one of those (its got a flat back)
cut it about and weld bits on?

[northeastcyclist]

I like the cottered bottom bracket idea. How hard are the cotter pins to remove? I've done abit of background reading and apparently this is abit of flaw, but seeing as this is quite mature technology, most bike shops will have tools to easily remove them shouldn't they?

Access to an engineering workshop is something I definitely don't have right now, with Newcastle Uni closed to students. Time and cost aren't necessarily on my side either. Compromising by using a file and relying on the bolt for security might be the best option.

I reckon I could grab that chainset you recommended 531colin, I could definitely stick the bits I need on there and work around that. That would be fantastic for a sort of one-off basis. I'd have to expand on that to consider shifting from 1 to about 100-200 a year, but I could get it to work.

Thank you for the help guys! I can't thank youse enough! I'm going to explore these avenues to see what works best. Might end up getting rid of the square taper in the end completly because of how much a pain in the buttock this thing is.

[slowster]

How hard are the cotter pins to remove?

I think the answer to that is 'it depends'.

seeing as this is quite mature technology, most bike shops will have tools to easily remove them shouldn't they?

Again, 'it (probably) depends'. I doubt most shops selling upmarket bikes will have any specialist tools, whereas a traditional local bike shop which sells and services fairly basic bikes would probably more likely need to be able to service a bike with cottered cranks.

See the following thread, which contains further links to other threads on the subject.

viewtopic.php?f=5&t=138525

[531colin]

Cotter pins? don't go there
How about external BB bearings?
Am I right in saying all you need to dismantle them is an Allen key? ...no puller? (and a tool to remove/fit the bearing)

[richardfm]

It can be done but it depends if one has access to a serious engineering workshop, it would however be quite a convoluted and time consuming process.

You would need a precision rotary table (or a dividing head) mounted on an x-y axis table, a set of broaches, slip gauges, sine bar and a broach press.

Also the component would have to be manufactured on an initial basis with a sacrificial stub for holding purposes that would be machined away after the taper was manufactured.

Probably quicker to use a file.

K

40 years ago when I was an apprentice marine engineer I knew what all of that meant, but after more than 30 years working in IT I have forgotten a lot of what I once knew.

[RickH]

Cotter pins? don't go there
How about external BB bearings?
Am I right in saying all you need to dismantle them is an Allen key? ...no puller? (and a tool to remove/fit the bearing)

It depends on the crankset - my Raceface one needs a puller to remove the drive side crank but it has splines (presumably tapered). It also has a "cinch" mount for the chainring(s), also splined (a much bigger diameter spline & held on with a screw on lockring) which could presumably be used to mount anything you like. I think Hope, SRAM &, possibly, some Shimano 1x use splined one piece chainrings.

[jb]

The only way to make a female square tapered hole to any degree of accuracy is by a wire spark erosion cutter. Most cranks will be forged round a male square taper as this is much easier but not necessarily for the home enthusiast. also you can cast an aluminium part round a steel taper mandrill for cheapo cranks.
Cottered cranks were used early on because they are easy to manufacture with crude tools and will form a tight fit if done right.