I have found endless opinions on mass-manufactured hubs that are either left-side-threaded or 'reversible' or etc. I am not seeking information or opinions on these.

I am also aware of the available aftermarket left-side freewheels, and though opinions on those would be welcome they are not directly related to this question.

I am seeking insights and/or technique advice for adding the threading needed to receive a left-side freewheel onto a steel hub that already has a right-side threaded freewheel but has a smooth left side (unthreaded, no coaster brake or brake disc mount).

Examples would be how you set up your jig to maintain linear alignment as you thread (if you did- and if you freehanded it how did you do that), how you managed the odd shape of the hub in clamping it for the work (without marring/damaging it), is there a particular die carrier/handle you recommend, what stood out as a hiccup or obstacle is setting up, was the small roundover athe very end a problem for beginning the threads, etc etc. Tips on execution and methods.

People will insist on the 'why' here, I suppose - I want to add a second, separate, driveline to the bike, and I do not want to 'double' the right-side freewheel due to layout needs. To reduce rolling resistance from the new driveline, it needs to have a freewheel.


OAL, bearing cap to bearing cap - 149mm

Bearing cap diameter - 35mm for 1st 7.5mm, then 36mm for 7.5mm

Bearing cap end to spoke flange face - 15mm

~7mm on the 35mm dia. section is usable as threaded surface

It's a 'fat bike' rear hub.


Hope someone here has some advice. It's a tricky thing to attempt if you don't have a machine shop.

  • I'm not sure on the physics but would a freewheel on the left require a reverse threading to counter precession? This may require a machine shop. – DWGKNZ Aug 10 '16 at 22:04
  • Yes, a left-side freewheel will need to be the reverse thread of the threading on the right side. This is so the forces applied by a forward-driving chain 'tighten' the freewheel onto the hub. If you threaded a 'normal' freewheel bearing onto the left side, you'd probably unscrew it when you applied any real force!! (not to mention a 'normal' freewheel would be freewheeling in that orientation.) – 111936 Aug 10 '16 at 22:10
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    @DWGKNZ I don't think precession is a concern with freewheels. The threads in a freewheel turn to directly transmit torque, and so they are threaded such that they tighten under load (whereas threads subject to the wiggling that causes precession are threaded opposite to the rotation). Of course freewheels have to be reverse threaded on the left side, because then pedaling would directly loosen them. – Kaz Aug 10 '16 at 22:55
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    @Kaz Yes, adding electric assist to a heavy bike. But I'm not using a kit, a hub motor, or anything 'normal'/'store bought'. Custom designed carrier under the seat for motor and jackshaft transmission, output on left. I live in a very hilly place and 'normal' ebike stuff is either underpowered or illegal here. It's a case of "Nobody has solved this particular issue so I guess I have to." As far as the freewheel - I desperately want to freewheel there at the hub, and not further forward in the gear train. Just want to sort out best attack method for threading it without a lathe!!!! – 111936 Aug 10 '16 at 23:24
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    @Kaz 1) Added a pic. There's no rotor mount present. Smooth steel. 2) Buying a new hub is possible but I really want to use what I have. 3) Based on the right side freewheel being present, I think I'll find a left side one that will work for the diameter of the hub. Didn't see that as a problem? 4) No need to cut the gear from a rotor when a front gear I already have bolts right on. – 111936 Aug 10 '16 at 23:37

Starting from the hub you have now is likely to be very difficult. It sounds as though you don't even have disk rotor mounts on the hub, so there's not a lot of structure there for you to attach to. Rather than getting caught up with how to weld extra metal on so you can machine threads onto it, it might be easier just to machine up a hub from scratch. The actual solid part of the hub is not at all complex, and since you will need a lathe anyway it would probably be easier to work that way than get into welding onto a hub that's not designed for the extra stresses you want to apply.

If you don't have access to a lathe you're going to find this project quite difficult. At some point, probably quite early on, you're going to need either a lathe or a large, expensive pair of dies to cut freewheel threads (a taper and square pair, since you need to cut right up to to end of the surface). Possibly two pairs of dies, because you might end up wanting a locknut on your freewheel thread.

More commonly people bolt a fixed sprocket to the disk brake mounts and drive that chain via a freewheel. It's not quite as efficient as putting a freewheel on the rear hub, but much simpler.

Some "put a petrol motor on your bicycle" kits attach a sprocket directly to the spokes, but it would be hard to overstate my dislike of that method. It is hard on the spokes, and hard to fix the wheel when those spokes bend.

The other easy-ish approach would be to flip-flop hub and re-cut one side to take a left hand freewheel. I haven't ever played with those, so I can't help you work out what thread is used.

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  • Thanks for the time, Moz, but I pretty clearly stated my question. I'm trying to find insight/info on the actual execution of this task. – 111936 Aug 10 '16 at 22:05
  • I've shuffled the paragraphs to put the bit you care about first. Does that help? – Móż Aug 10 '16 at 22:08
  • 1) Yes, it will not be easy to do this. 2) The right side is the same construction as the left side, and the right side is threaded. Thus, the steel is thick and strong enough to take threads already. 3) I do not have a lathe, and while challenging I know that doing this without one is possible. As stated, this is really what I seek advice and input about. 4) Again, yes it isn't going to be easy. Got it. Still want to do it. 5) As for the rest, please re-read the first two paragraphs of my question. Not buying a hub. Also - there are no flipflop hubs for a fat bike rear that I have ever found. – 111936 Aug 10 '16 at 22:24
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    In that case I don't understand your question. You have the tools, you know it can be done, you don't want contrary advice, you're asking for... reassurance? – Móż Aug 10 '16 at 22:27
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    @Nixt I think if you're not a machinist, you kind of have to become one first to do this. Have you created interior or exterior threads before in any material, of any size? This doesn't exactly seem like a "hello world" exercise. I don't think you can do this without a lathe; you might be able to do this with a cobbed-together jig that isn't formally a lathe, but is de facto a lathe. The hub has to spin around its axis, while a tool cuts away the material to create a precise cylinder of the right diameter which can then be threaded. – Kaz Aug 10 '16 at 23:12

Doing this without machine tools would mean using a die. Left drive freewheels have left hand threads in 1.375x24 and M30x1, and M30 is too small here. Off the shelf dies exist for neither in left threading.

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  • Thanks for the input re: getting the dies. Will now have to investigate. As to diameter of freewheels, this page has nominal 34mm I.D. left side freewheels that appear to be the same as what's on my bike's right side. electricscooterparts.com/freewheelclutches.html – 111936 Aug 11 '16 at 21:21

note for this solution you will need 2 identical sized hubs)

i had that problem with a project hub like the one in the photo its steel and 3 pieces its a pressfit hub

i resolved the issue by cutting a notch in a 2x4 large enough to accept the hub shaft then tapping on the inside of the hub (blank side down) with a metal rod and mallet (same way you tap out a bracket cup) and rotating the hub in place every 2 or 3 taps until the assy came apart i did the same to a identical donor hub dropping out the threaded hub cap crown then rebuilding the first hub with the donor crown again tapping and turning until set

note prior to dissasembly on both hubs i scratched a center line under a spoke hole on both the shaft and crown assy to keep offset alignment

also its a good idea to scratch a line around the whole shaft at the base of the crown so youll know how far to tap the donor crown back in place (if you have access to a cheap bench press all the better!)

yeah the cheap asian hubs have that going for them this trick only works on them enjoy you can send beer if you like! whoop didi hoop didi poop didi scoop xD

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  • Even if it would be possibile to source such a hub with the lefthand thread needed for the purposes of this question, I'm pretty sure reassembling a hub body like that beats the purpose of having extra reliable transmission in the first place. – Walto Salonen Oct 26 '18 at 7:59
  • What is a threaded hub cap crown? What process are you describing? There’s something about the terminology that I can’t follow. – Swifty Oct 26 '18 at 14:22

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