So, I got to thinking about double hole cranks and how to make them. I’ve thought about this in the past and the common response has been to have them done by a machinist. I have done a lot of ski binding mounting and I thought a similar jig could be used to drill multiple pedal holes in cranks as long as there is enough material to support it.
Today I was thinking about it again, and came up with this idea to modify slightly a self centering doweling jig. My idea is to make one hole with an attachment that threads into the existing pedal hole. This would square the jig to the crank. Then you could use one of the other holes to drill your new pedal hole. It would be nice if the holes are 20mm’s or so apart, but that would be something to modify if they aren’t.
The nice thing about the jig is that you don’t need a drill press to get a hole that is square and centered. I have used similar jigs on skis with metal top sheets, and they have always made perfectly aligned holes without a drill press. I think this could be an easy way to make double hole cranks for your disc setup.
Once you have the second hole drilled and tapped you should be able to use the jig to set the third hole off of the second one. As long as there is enough crank material I don’t see why it wouldn’t work.
I might pick up a pair of Sinz or Origin8 cranks to try this out. The jig itself is between $13-$60 depending on quality. I’m thinking of drilling the cranks, and bringing them to my local bike shop to tap them. If I was going to do a lot of these it would make sense to just buy the taps.
Pedals are 9/16x20, and yes you need a left hand thread and right hand thread. You can get a set of taps for $20-30 if you want to buy them, but if you are in with your LBS a lot of them will let you use their taps in the shop, or charge a nominal fee to tap them for you.
The machinist comes in with drilling the hole and I think the jig idea could remedy that.
Well, I just picked up some Dotek BMX cranks off of Ebay for $10. I’m going to wait to hear more responses to this thread before I go for it, but barring any great insight to the contrary my plan is to make them dual hole.
They have already been machined down to 140’s, and they look like I could easily put a hole at 120. I don’t know if I want to go shorter than that, but for kicks I might put one at 100.
I really like 140’s on my Coker so it’s a perfect place to start for me.
I can’t wait to get you a brake rotor! our prototype batch and sample rotor from the fabricator have all been mounted up… we’re just waiting the first production batch! I don’t know when the bolt on will be made available, is your rig steel?
It’s a Nightrider frame, and from the pix you’ve put up I’m pretty sure your bolt on mount will work. I have a couple of ideas for mounting the caliper that I’m going to try before I commit to your mount. Your mount looks like it is more than adequate to secure the caliper, but I think there might be a simpler solution. In truth I might be more inclined to braze a mount to my frame if it came to it. We’ll see how it goes. Do you have a time frame for releasing the rotor?
not yet, it’s the fabricator’s terms… hasn’t released a quote so we don’t know what to pay. I will be making a weld on mount soon, a braze on would be a little bigger so you can stick it into a slot that you make in the frame to fill with molten brass. know anyone that arc welds?
I have a friend with an arc welder, so that won’t be a problem. I hadn’t considered welding but that’s probably the route I would go considering that my friend lives around the corner from me, and he’s always game to weld stuff.
As for brazing, I have done plenty of butt joints with a small fillet of brass. We used to braze Mafac canti studs on frames at the bike shop I worked at and they were solid. I don’t think you would have to cut a slot in the frame to have a good brazed joint, and it’s something I could do with a MAPP torch.
These cranks will be ready for a rotor for sure. Now if I could find aluminum chainring bolts that match the color of my Nightrider…
The holes on the drill guide are spaced 3/4" center to center. That works out to 19mm’s. I wanted 20mm’s, so I think I can live with 19. This will make my cranks 140,121, and if I decide to put a third hole in 102.
The cranks should be here in a couple of days. I’m going to go to the used too shop in town to see if they have the doweling jig; otherwise I’ll probably pick up a cheap one from Harborfreight.
I still need to figure out how to attach to the existing pedal threads. Any ideas?
I’m an older rider that has alot of bicycle experience and parts/toys. So when my kids were young, to take them on the tandem I put adapters on the cranks so they could pedal also, by shortening the crank length. These were available at the LBS. and will not ruin a “hollow forged” crank that alot of manufacturers are puting on Uni’s. So guys its up to you to decide. These are for 1/2" 20 pedals, but I’m sure KB1JKI might want to make up some for you if you are nice. These I don’t use so if there is interest I will let them go. These went under the name “Dawin’s Pedal Adapters” (79 cents)
I’ve seen your posts and your work out on the threads! If I can get them built, it would be cool to play with but these guys really worry about Q. I don’t think those adapters would like hopping too much either. The simplicity is good.
We would like to specialize in unicycle solutions.