[PepperJester]

So I'm not much of welder but I like to tinker in the shop and do have some machinist background so have been thinking of going ahead and making a set of cranks for my xc bike.

I don't fee that making the arms and a bolt on spider will be any stretch of my skills but making the bb interface has got be stumped.

I'm thinking a square taper set up would be the least amount of hassle but am open to suggestions. I only have basic hand tools at home but can trade free shuttle days with some of my machinist buddies if I need to borrow a mill for an afternoon.



Any help would be great.

 

[schneidie]

Square taper won't be too horrible to make, but I'd be sure to heat treat whatever you're working on if you do any welding on the part at all.
Trying to do ISIS or something like that would be a real b!tch because the interface is fairly complex. I'd invest the time to make interface very precise, as you will round it out if you don't. Talk to your machinist friends and see what they think. I only have 4 years experience, so I might be spewing a load of sh!t for all i know.

 

[buildyourown]

Machining the square interface will require a 5-axis mill. You may be able to do it on a nice 3 axis if you have some decent CAM software.
The interface is pretty sensitive to tolerance. If you get the taper wrong or sloppy, things won't fit for long.
The ISIS is actually much easier to manufacture, but it requires the purchase of a wicked expensive broach.
Sorry I can't offer much help on how to do it, but you should know that it is hard. I year of 5 axis programming experience and I would consider the square interface difficult. Good luck.

 

[shiggy]

So I'm not much of welder but I like to tinker in the shop and do have some machinist background so have been thinking of going ahead and making a set of cranks for my xc bike.

I don't fee that making the arms and a bolt on spider will be any stretch of my skills but making the bb interface has got be stumped.

I'm thinking a square taper set up would be the least amount of hassle but am open to suggestions. I only have basic hand tools at home but can trade free shuttle days with some of my machinist buddies if I need to borrow a mill for an afternoon.



Any help would be great.

I would do a design for an external bearing BB. The arm is welded to the spindle on one side and you can make some sort of spline/keyway and pinch bolt for the other side.

 

[pvd]

Take a look at the Groove cranks.

 

[PepperJester]

link? I'm not formula with the Groove cranks. Google was not much of a help either.

 

[D.F.L.]

Splined interfaces are broached. You just need the right equipment. (in other words, anything but square-taper is probably going to be too expensive for one-offs)

If you're willing to weld some steel cranks, I imagine the appropriate splined stock is available. I'd go with a 2-piece design.

 

[rustola]

link? I'm not formula with the Groove cranks. Google was not much of a help either.

I believe he's talking about Grove innovations cranks

 

[Schmitty]

Yep broaching the splines would be easy.. I would consider it easier than dealing with sq taper. A lathe can broach/index pretty easily. You'd need to figure out the correct id of the crank arm, and geometry of the splines to correctly grind an (hss) bit, or better yet have a custom carbide one ground. You can also buy spline stock.. in which case you'd have to braze it into the arm.. maybe not a great idea, and I don't know if the bb spline specs are 'odd ball' or not.

A horizontal mill would broach pretty easily as well. .. holding the crank correctly would be the crux I think. If the part of the crank where the bb would interface was round, you could do it easily in the chuck/indexer, then weld that assembly to the arm afterward.. distorion being minded.

-Schmitty-

 

[DWF]

Machining the square interface will require a 5-axis mill. You may be able to do it on a nice 3 axis if you have some decent CAM software.
The interface is pretty sensitive to tolerance. If you get the taper wrong or sloppy, things won't fit for long.
The ISIS is actually much easier to manufacture, but it requires the purchase of a wicked expensive broach.
Sorry I can't offer much help on how to do it, but you should know that it is hard. I year of 5 axis programming experience and I would consider the square interface difficult. Good luck.

You might be overthinking it. A square taper is the easiest to do and the reason it's been around so long. Drill a hole through the stock slightly smaller than tangent of the flats, mount crank arm at 2-degrees for taper, insert broach in arbor press, presto-chango you have crank flats. If you have a milling machine, you can use a common 2-degree tapered end mill and rough them in without having to move the crank arm at all. With some BB designs, you hardly even have to clean up the corners.

Isis is easier to do on BB spindles than cranks, but still works the same way. You just drill or interpolate the center hole and the slots can slightly deep meaning you don't have to do a final broach. Same with most of the new external types. If I was going to make small batches of my own cranks with a splined interface, I'd wobble them in and you could do it all on manual machines.

 

[D.F.L.]

Wow. Do all machine tooling companies use '80s-era Val Kilmer-style action-flick music in their videos? Painful.

Rotary broaching tools look expensive. (actually, they don't LOOK expensive, but I'm sure they are). I'd probably just weld both crankarms on and hope for the best

 

[buildyourown]

Rotary broaching heads aren't that expensive (compared to other machine tools)
We bought a head and I think it was only a couple hundred $$$. Finding a bit that matched the ISIS would be custom though.

Don, having done some tapered broaching, I think it would be very hard to control the timing and the size well enough. Yes you could do it but it would require an fairly complex and accurate fixture. As for the tapered endmill, I suppose it would work. Again, size control on a manual machine is going to be tricky. Maybe square tapers aren't as sensitive size as I think. I honestly haven't worked on them in 5 years.

 

[Rody]

PepperJester,

If all the above talk has not confused the snot out of you, I'll put it in simple terms;

For someone who is "not much of a welder" who likes to "tinker" in the shop, a crank project is an overwhelming undertaking.

Mucho custom fixtures are required for both machining and welding to insure spot on accuracy. As the piece is a high stress component with multiple load directions, your fabrication skills MUST be at the top of the game, and as you are seeing, there are many specialty aspects that must be learned or farmed out, including potential cnc shop time, heat treating, plating, etc...

The cranks I've worked on or built have all required more time in preparation (design, fixtures, contract work/sub processes) than actually fabricating the pieces into a solid piece.

So,my advice, choose another aspect of the bike that you can individualize and make your own that requires a bit less experience and time.

BTW...here's a pic of the cranks PVD was referring to...

and a link www.grovecycledesign.com

cheers,

rody

 

[Schmitty]

You can do it in a lathe.. make a cross slide stop to set depth.. creep up on it, try the fit, crank the compound a few more thou to open it up. Figuring out the angle of the bit would be the hardest part.

 

[DWF]

Rotary broaching heads aren't that expensive (compared to other machine tools)
We bought a head and I think it was only a couple hundred $$$. Finding a bit that matched the ISIS would be custom though.

Don, having done some tapered broaching, I think it would be very hard to control the timing and the size well enough. Yes you could do it but it would require an fairly complex and accurate fixture. As for the tapered endmill, I suppose it would work. Again, size control on a manual machine is going to be tricky. Maybe square tapers aren't as sensitive size as I think. I honestly haven't worked on them in 5 years.

Timing as to the location of the flats or timing the stop on the broach depth? I'd index off the pedal eye for location. For depth of the taper if you use a tapered broach it's just a collar stop, the broaching is actually the easy part. Having seen square tapers done on cranks, you wouldn't believe the hack ways some outfits did it including stomp forging the shape in it which is probably a better way for Al cranks. A lot of times with the bike industry you have to think blacksmith and although that's changing fast it's pretty much how a lot of stuff got done.

 

[DWF]

PepperJester,

If all the above talk has not confused the snot out of you, I'll put it in simple terms;

For someone who is "not much of a welder" who likes to "tinker" in the shop, a crank project is an overwhelming undertaking.

Mucho custom fixtures are required for both machining and welding to insure spot on accuracy. As the piece is a high stress component with multiple load directions, your fabrication skills MUST be at the top of the game, and as you are seeing, there are many specialty aspects that must be learned or farmed out, including potential cnc shop time, heat treating, plating, etc...

The cranks I've worked on or built have all required more time in preparation (design, fixtures, contract work/sub processes) than actually fabricating the pieces into a solid piece.

So,my advice, choose another aspect of the bike that you can individualize and make your own that requires a bit less experience and time.

BTW...here's a pic of the cranks PVD was referring to...

and a link www.grovecycledesign.com

cheers,

rody

Yo Rody - Is that a 19mm spindle? Might have to pick a set of those up from you.

 

[Thylacine]

Rody, on the Hot Rods, it looks as though the pinch bolt doesn't exert any clamping force on 2/3rds of the spindle. Is this the latest incarnation of the design, or is there a newer one?

I still think the Sweetwings were way ahead of their time. It would only take some small mods to make them the ultimate steel crank.

Having said that, Sweet Parts has morphed into EE Cycleworks and they're working on an Aluminium version which looks really promising.

 

[DWF]

Rody, on the Hot Rods, it looks as though the pinch bolt doesn't exert any clamping force on 2/3rds of the spindle. Is this the latest incarnation of the design, or is there a newer one?

I still think the Sweetwings were way ahead of their time. It would only take some small mods to make them the ultimate steel crank.

Having said that, Sweet Parts has morphed into EE Cycleworks and they're working on an Aluminium version which looks really promising.

If you look at the design and it's manufactured to close tolerance, it should equalize. Tightening the clamps forces the spindle forward into the front lobes.

Hey Warwick, on the EE stuff, did they get the rights to Sweet Wings or is it the same guy?

 

[Schmitty]

Question for Rody

PepperJester,

If all the above talk has not confused the snot out of you, I'll put it in simple terms;

For someone who is "not much of a welder" who likes to "tinker" in the shop, a crank project is an overwhelming undertaking.

Mucho custom fixtures are required for both machining and welding to insure spot on accuracy. As the piece is a high stress component with multiple load directions, your fabrication skills MUST be at the top of the game, and as you are seeing, there are many specialty aspects that must be learned or farmed out, including potential cnc shop time, heat treating, plating, etc...

The cranks I've worked on or built have all required more time in preparation (design, fixtures, contract work/sub processes) than actually fabricating the pieces into a solid piece.

So,my advice, choose another aspect of the bike that you can individualize and make your own that requires a bit less experience and time.

BTW...here's a pic of the cranks PVD was referring to...

and a link www.grovecycledesign.com

cheers,

rody

Hey there Rody, what is your crank bringing to the market, performance wise, that isn't already available? Mad strong? Stiffer? What's your thinking.

They look great. Can you run 3 rings with them?

-Schmitty-

 

[Rody]

Hey guys, not much time so I'll hit the highlights.

The pinch bolt (older design, now uses opposed 4mm cnc machined piece) serves only to secure the arm onto the spindle, not to tighten the interface of the tri-coidal polygon, which tightly slides into place. The three lobe shape offers superior surface contact area over all other splined/isis/taper designs and is therefor, much stronger. This is the same design that is used on drive systems for military tanks.

It is mad strong and stiff, and can run three rings with an aluminum spider plate that fits the right arm. The crank fits the Shimano standard for external bearing use. Does the market need another choice? Probably not, but they are pretty cool all the same

It should be noted, however, that this is not a "new" product to the market, just a re-design of the first two piece crank that Bill Grove developed in the 70's.

Warwick, the Sweet Wings were nice pieces, until they broke. They feel prey to the chase of light weight, as did an early run of the Hot Rods. Who would of thunk you'd have 200 pounders hucking off of 10 footers and then complaining when their cross country cranks failed Regardless, I always wanted another pair...I'd love to see them come back

Gotta hit the sheets for a few hours...show prep sucks!

rody