Bb30 crank spline standard (NOT BB STANDARD)

[crowe-molybdenum]

I’m in hot pursuit of a drawing/specification for the quasi-standard that is the 8 lobed tapered spline that we see on the end of a bb30 spindle; something like this

I want this because I want to draw and have made a pair of cranks which can interface with existing available spindles.

I am not interested in information about the bb or frame standards, that is readily available with a quick google search.

the best/closest resource i’ve found is this thread on Vital MTB

https://www.vitalmtb.com/forums/hub/bb30-standard

most of the thread is spent explaining that the frame/bb standard people keep posting isn’t what is being looked for… but there is a post at the bottom with the beginnings of a drawing.

I’m not near anyone I could recruit to machine this, and shipping to/from my part of the world is a total joke (6 months corrupt customs delay not unheard of)… so I’m trying to avoid a test cut here; ideally a drawing with SOME verification would go some way towards minimising the ever growing amount of scrap I see to produce

willing to share finished designs if my incredibly esoteric wants are something anyone is interested in too… ( yes, these are for my adjustable bb height track bike)

[Daniel_Y]

I would reach out to Sturdy Cycles, they make a printed crank. No idea what spindle standard they use, but I’m sure they have a better idea.

Titanium 3D printed crankset - Made to order — Sturdy Cycles

[crowe-molybdenum]

thanks for the reply,

I have reached out to Tom, he replied: “Unfortunately it is not an open standard that I could find either and so I developed my own which is not likely to be of very much help to you”

so while that looks like the splines we know, it just may not be.

[stevenshand]

I don’t think that you’ll find what you’re looking for. I did similar work when looking into crank interfaces for the Intra-Drive (www.intra-drive.com) drive unit. I’m not saying drawings don’t exist but they are likely to be proprietary. I was unable to find anything open other than ISIS.

[floppywonka]

if you have access to a 3d printer, you could start from scratch by taking measurements from the spindle in question and start drawing. once you think you’re close you can print a donut with the spindle hole in the center and see how it fits, make adjustments and print again, etc until you have something useable, and then you can get it machined from metal.

i did this with raceface’s cinch interface and it worked well for me

[floppywonka]

also, the post you linked is less than a year old, you could probably make an account over there and hit up the digit bikes person with the model and see if you can get the info from them

[crowe-molybdenum]

thanks for the thoughts team.

I have reached out to digit bikes; he has said that he is now using that drawing to produce spindles which work with existing cranks with no problems. so thats certainly something.

Ive been doing some thorough measuring of the cranksets I have on hand, and will have another measured up by a trusted third party within a few days all going well,

(here’s the dangerous assumptions part)

IT APPEARS that the crank splines are “the same”, but they extend between 1.5 and 1.6mm further outboard (following the same form & taper) before ending with a surface square to the spindle centreline.

IT APPEARS this surface is bottomed out on the end of the spindle at or before the recommended torque ( the cranks I have are all at least lightly used )

I don’t know enough about designing splined interfaces to apply occams razor and say this makes sense… but I don’t know nothing and this is feeling like an arrangement which I think i’m willing to try. ill get those other cranks and spindles measured and make a call.

as for the 3d printer idea, thats a nice approach for the application you’ve shown, because unless your riding that crank arm fixed gear (in which case, you’re rad, and further power to you) those splines only have to resist torque in one direction (the crank arm trying to turn when you pedal, and the chainring resisting that turning); any slop or slack is quickly taken up and then remains “rotationally bottomed out” which means it doesn’t cause any issues.

in contrast, the connection between a crank-arm and spindle has to resist (among other things) torque which alternates back and forth in clockwise, and then counterclockwise directions every pedal stroke. which means any freeplay or induced play (by the deformation of the crank) rocks back and forth and wears the splines out.

thus crank splines are far more precisely made, and almost always tensioned radially (via a taper or a pinch bolt or two).

Ive ruined a bunch of cranks and chainrings by trying to get away with riding splined chainrings or spiders fixed gear, and without fail, that little bit of available play slops out real bad, real fast.

[earle.b]

The Cannondale Hollowgram cranks were I think the first to use this interface.

Someone has posted a cad of Hollowgram cranks on GrabCad years ago.

Free CAD Designs, Files & 3D Models | The GrabCAD Community Library

You could 3d print this to verify it’s accuracy.

[PaulD]

Can’t guarantee this is accurate, and this version has a shoulder on one side. Let me know if it checks out!

[crowe-molybdenum]

this hasn’t stagnated, its simply been moving at egypt - speed.

I received back (from my newly discovered local ‘guy’) a test part!

some good learnings.

first up- the splines.

the splines on this part are cut from a drawing I created by balancing the above contributions, measurements I took from the 3 bb30 cranks I could get on hand (all cannonade branded) and measurements I asked of a trusted friend who also had a crank on hand. (shoutout David at Goat Cycles Christchurch).

the splines created here are measurably the same depth as the drawing.

when they push onto a spindle by hand, they go on the same distance I would expect from the drawing, leaving an mount to “do up” which is very similar to (/within the range of/) all the other cranks I could get hands on. when done up to an array of torque numbers, they move onto the spindle very similarly to the other cranks I have on hand, and they end up bottomed out in the same position, at the recommended torque.

if I colour in the spindle with a sharpie, and install the crank arm, it takes a reasonably even pattern of about half the sharpie off.

so I think i’m pretty happy with that. enough to press on and try them IRL anyway.

next up; the extractor cap threads.

SO, I naively measured ONE set of extractor cap threads, and presumed they were also a defacto standard.

they are not.

upon further investigation m25x1.0 is in use with 18mm bolts (some cannonade/fsa bb30) , m26x1.0 is in use with 15mm bolts (mostly gxp) , m30x1.0 is also in use with 18mm bolts. (most sram dub/bb30)

I initially measured the threads at m25x1.0 at a ~6m depth. so thats what I called out on the drawing, the machinists duffed this thread, leaving a ragged ~25mm hole so I pondered increasing the size, for the sake of this test, and googled it. at this point I discovered m26 and m30 options so I asked him to increase the size to m26, thinking I could make a custom extractor cap and use the cannonade bolts I have on hand.

he then duffed the m26 threads…

so i’ve been removing this crank arm from the test spindles with a gear puller…

but I think anyone designing cranks going forward likely wants to use the m30x1 option, so as to make sourcing (both original and replacement) bolts and extractor caps as simple a possible. the m25x1 does appear to still be in use, and this option could be nice for its smaller size requirements in some cases.

(NB: opinion: these bolts break in time with normal use, I think the listed torque is unnecessary)

pedal threads;

I couldn’t find any 9/16x20 taps at all here, let alone a L&R pair, so i’ve ordered them from overseas, and will likely end up cutting these threads by hand after the fact. ill make some sort of block or machine setup arrangement to get them square.

the taps are now on the way, but out of interest, on paper M14X1.25 ( much more readily available tooling in my neck of the woods) is pretty close to 9/16X20. I know people have used m14X1.25 taps to chase 9/16 pedal threads, as nervous as it makes me . and I know I could test this very easily, but I’ll ask anyway. has anyone here MADE a, m14x1.25 thread and put a 9/16 pedal in it?

id LIKE to say it shouldn’t fit…

(yes I know this is also an old French pedal thread standard)

.