UniChris

My total experience with wheels consists of diving in and building a 29" city bike type wheel from all new parts for one of my unicycles, which I was able to get quite true against a dial indicator, and now trying to re-true a much heaver section giant 36" rim that I've been putting all my miles on, and which has occasionally needed a spoke replaced.

Essentially, if I go around the wheel and get everything to a comparable pluck tension, it runs fairly true, except that there's a wobble to one side easily seen in comparison to the brake pads right where the pinned joint is. Playing with tension there doesn't seem to affect that, so I'm starting to suspect it's an issue in how the cut ends of the rim where finished. If the wheel were unbuilt it would be fun to set it on a big surface plate...

Does my suspicion seem logical, that this is just a flaw in the rim and not something correctable via spoke tension? There doesn't seem to be any problem with it, the sidepull brake caliper floats enough to accommodate it, and anyway the brake is only useful for drag on gradual hills.

Even though smaller than the outline of an assembled DF bike, the big wheel doesn't fit in conventional bike racks meaning it's not officially transportable on long distance trains, so for some planned adventures (like trying the C&O or Erie Canal) I've been looking at copying an idea I saw someone do, of sawing the rim in two additional places and creating two additional pinned joints to make the whole thing pack down for travel, then build it up at the destination. If I start to look at the cost of one-way car rental vs. train fare that nearly covers the cost of parts of getting another rim, hub, and set of spokes, and I'd rather build a wheel in a motel room than drive 5 hours... especially if it meant a bailout option of taking it apart again to get on an unplanned bus or train home. Sort of thinking if I were to do that I'd buy another rim new, and then cut whichever of the current or new one had more wobble...

jbucky1

Unless its an utter garbage $10 rim, you should be able to true out the lateral movement at the rim weld / joint. Some rims are better than others, generally the more expensive, the better they have been manufactured

- james
www.buckyrides.com

UniChris

How, and at what cost of tension difference? I could understand that being true with a smaller more flexible rim, but this beast is 42mm wide and 24 deep.

Moe Zhoost

It's not uncommon to have a bit of an imperfection at the joint of a rim, but I wouldn't characterize it as a wobble. My experience is that it won't be something that you would be able to fix with spoke tension. I either tolerate it (because you really only feel it under braking) or if pronounced I will gently file it flat.

Sawing a rim in half is insane (sorry, couldn't think of a nicer description). First, by sawing the rim, the saw kerfs will remove small arcs that will change the diameter of the rim (tire fit issues). This metal removal will also reduce it's roundness and that may affect ride. I'd explore shipping it as baggage or send it by UPS ahead of your travel.

Even though I think the idea is nuts, I would really like to see you try it out. If you do, please post details.

jbucky1

Unless the rim is bent, its totally do able and have "good" balance and tension. Maybe go to a wheel builder so they can show you the steps.

jbucky1

YES! exactly. Insane.

UniChris

In effect an area of around 3-4 spokes spanning the joint visible moves to the side then back. Filing the high side wouldn't really help, dressing faces of the joint itself (once I had it in pieces) might, but we share a concern about removing material there. I'm thinking the ends weren't properly re-curved after whatever the factory cutting process was.

Thirds actually ;-) I wouldn't have thought of it, except that it's been done before by someone who was quite pleased with the result. They allegedly used a hacksaw, I'd definitely be trying to find something with as thin a kerf as I could and test it on some other aluminum extrusion first. And of course I'd build up the wheel and try it before I set off with it on an adventure.

I don't know that a shim would be impossible, it's loaded in extreme compression after all.

That's an option I've looked at, but it also requires finding suitable packing material at the end of the ride like a flat screen monitor box to re-engineer (we're talking 36x36x10 to the ends of the axle). That then gets me thinking that even though the rim is rather pricey at $130, it might be worth the experiment compared to bi-directional shipping.

I think the best "ordinary" option particularly for a supported tour I'm looking at would be to find others to carpool with (especially tandem or trike folks who can't do trains either). But knowing I could pack down small would make the idea of tackling a ride at my limits, but which has train service along the way, feel a little more comfortable. Of course in such an eventuality I could also just abandon a rim, though I think I'd buy a cheap hacksaw and cut it in the field on the hope I could still put it back together at home.

Moe Zhoost

Yes, if it spans that many spokes you'll have to play with the tension. Bike rims are made by rolling the flat extrusion into a coil of 5-6 loops that is then cut at the top to form what look like split lock washers. The split is then aligned then pinned or welded. Understandable that there is a bit of stress here. If the wobble is significant and doesn't respond to normal tensioning, I'd say it was an off spec rim.

Jeweler's saw. If you have connections, Wire-Cut EDM would do a great job. I'd skip the shim idea for fear that a shim would go adrift and slice the tire.

How 'bout making a vest for it and saying that it's your emotional support wheel?

IGood luck whatever you do. If you do try the 3-piece experiment, please post pics and comments.

UniChris

That is genius! And not far from the truth.

Just took the tire off again today to verify that some embedded bits of rock had not poked through, was able in the process to confirm that it can sort of fold smaller, but also finally realized that the bare rim has a diameter of 31 3/4 inches... which would fit in larger bike boxes, but none of the relevant train stations have baggage service...

Wilfred Laurier

Does this rim go on a unicycle with a rim brake? If not, then it sounds like all is good and you can stop worrying and ride the thing. A mm here or there effects nothing if you don't have rim brakes. The tire will naturally make a straight riding surface and you won't notice a wee bit of lateral run-out in your rim.

UniChris

It does but the slight wobble has not been an issue, the caliper has a decent amount of float and the brake is really used for drag on mild descents than literal stopping.

UniChris

Decided I needed to stop contemplating this take apart wheel thing and get the parts and see if I have the courage to take a saw to it. Ordered the spokes on Friday, touched base with the guy who first tried the idea, and ordered the rest of the parts this morning.

Half thinking I may try to find a beat up rim to experiment with the sawing technique on... as long as its double wall and aluminum it should be representative of the problem even in a different size.

Verified the existing rim is pinned - the pins are ferrous and will just barely support an odometer spoke magnet out to their ends.

Originally I was going to cut my existing rim and build the new one up conventionally, now I'm not sure - existing one is from a budget model and doesn't have eyelets but new one does (even though they're really the same rim), which seems a plus for a wheel that may get rebuilt several times for travel, so may just end up cutting the new one. But think I will first at least built it up enough to verify that the rim is reasonably true in delivered condition, before doing unspeakable things to it.

Bill Kapaun

Some stainless steels are slightly magnetic.
I would suspect SS. Else, you could have rust discoloration of the joint when it got wet.

ThermionicScott 

If the rim is pinned rather than welded, consider using a hammer and blocks of wood to knock the joint straight instead of sawing it up.

UniChris

Indeed, and a negative result with a magnet wouldn't have ruled out stainless, either.

Good point... had been thinking of possibly using annealed drill blanks if I found I needed pins in a difficult size, but rust would be a reason not to. The guy who did it before used brass pins.

In theory you don't need anything beyond some tape wrapped around it to hold the joint until the spokes are loading it in compression enough to hold together, but in practice I'm going to use pins.

Might even use pins and an internal joiner if I can find something suitable.

But confirming that the original condition is pinned and not something like an epoxied in sleeve should make it simpler to convert (the other guy had used a different and now discontinued rim)

UniChris

Two different goals.

One was slightly improving a current wheel that I noticed had some wobble at the joint that didn't want to true out while replacing a spoke. It's broken enough over the past year and the nipples are starting to get rounded so I'm planning to start over with new spokes and nipples as soon as all the parts come in.

The other is making a wheel where the very large rim comes apart in three sections to so the whole thing can fit in a suitcase.

That's the one that would get sawn, though it's not yet determined if I'll cut the existing well used rim or the new one... would cut the old one, but the new has eyelets which I'd prefer for something that may get taken apart and put back together several times this summer. I suspect that if I take apart the rim that has wobble, taking the tinyiest bit of material off the high side would bring it back, but too much would make it worse.

Another reason I'm looking for a beater rim / wheel to experiment on first...

Bill Kapaun

IF you are disassembling the rim on a regular basis, you can wipe off rust/apply a bit of grease before it would be noticeable.
If you could find some steel fence wire of the correct diameter, it's about as soft of steel as you get.
I'd think you wanted something easy to bend, but a snug fit.
Copper electrical wire? Maybe there's a gauge that's "just right"? I don't know if the strength is sufficient. It might be if your cuts/arcs are "perfect"?

I would definitely practice on at least one junk rim. There's bound to be a "quirk" or 2 that's not anticipated.

UniChris

Yes, but I'm not going to take it apart gratuitously and I only really have room to store one assembled, so if the segmented is working well my ordinary wheel will probably get stashed at relatives who live near some nice trails, meaning the take apart one is going to be together as my daily driver except when I'm traveling with it and may stay together for long periods of time.

I don't think it needs to bend, at least not much. More I just wanted to make sure it would bend not fracture.

Other guy used a drill as a lathe and made one side of his brass pins a hair smaller, can do that but trying to keep tolerances as tight as I can. Actually I'd almost rather they not be captive as packing would be easier without the pins sticking out... though I could make 3d printed "end protectors"

Hmm, interesting idea, if the rim wears it might benefit from larger pins later...

ThermionicScott 

Ah, now I get the idea. Jobst Brandt described how a wheel could be built out of 36 segments of a cut-apart rim, but you would not want to be riding it if a spoke broke! I can't find a reference whether he actually tried that or was just working from theory.

UniChris

Brandt proposed doing it. Musson actually built one up (which he had no intention to ride) with two extra cuts each side of the joint that were merely wrapped with tape (but not pinned) during initial assembly and then fought to break it eventually resorting to wood blocks.

I'm not riding anything unpinned though!

Russ Roth

Quick trip through a bandsaw with a nice, fine tooth blade will slice the rim cleanly and quickly. As long as you have tight fitting pins I don't see why this wouldn't work but I also can't see wanting to disassemble and reassemble a 36 spoke rim on a regular basis without a truing stand and tensionmeter. Not going to be an easy job.

UniChris

Not really that bad, unicycle wheels typically get built in the frame anyway since their axles won't fit in an ordinary truing stand. They're pretty simple as wheels go.

But first contemplated trip is one where I can get to the start with it assembled, it's the ways of getting back home where the size gets hard. Taking something apart in the field is quite a bit easier.

Putting it together away from home would wait until I've done it a few times and it's something I am confident I could do the night before a ride and still get to sleep at a decent hour. For a supported trip where I don't have to ride with or abandon everything I bring I might pack a wimpy power screwdriver with a nipple driver bit, but the bit on a dowel to roll between fingers shouldn't be that much slower.

Have to sew up some bags for the resulting pile of parts, too...

And as much as anything, there's the realization that the only way I'm going to stop wondering about this is to do it.

SJX426 

I place my bent rims on a glass coffee table or a kitchen island top made of marble or equivalent. Those surfaces are flat enough. I then mark where the bend leaves the table. Those spots get clamped down on the edge of a workbench with the bend down. The center of the bend is then forced up. One must recognize that there is still a lot of plasticity in the rim so you have to go further than where you think it will be flat. Repeat until straight. For small sections, support the two start points and use a C clamp. A block of wood in the U helps keep the sides uniform.
An example, just bent in a different direction.
P1030738, on Flickr

UniChris

Current challenge is to figure out how to separate the factory joint at least enough to cut the pins for individual removal, without damaging things overall.

Geometrically it would be easier after making the additional cuts. But not sure how to get a grip on the pieces, so thinking about ways to do it first.

In the factory a band clamp around the outside is used to close the joint. The opposite would seem to be tossing it around a truck tire and inflating that. Only at around 29 5/8" ID (because it's a 36er) that's not a common size. I do have a couple of 29er bike tires, but with rounded enough profile that keeping that aligned to the rounded inner profile of the rim would be hard - though if I find a rim that isn't in a wheel (perhaps the sacrifical one to try the sawing) plopping the whole thing on the floor with some wood blocks in between, flipping a table over on that, sitting on that with the mini pump might work.

Or there's the idea of cutting a bunch of 2x4 scraps (or kids building blocks) and using them as "barrel staves" to line the rim and drive a wedge between the two at the joint. The geometry works, it's the keeping it from imploding that seems hard.

Still have a few days to think, spokes aren't here yet and want to do at least a partial build to check things before ruining them...

ThermionicScott 

I'd think that if you can pull the joint apart at all, you might just pull it the rest of the way open and file down the protruding ends of the pins a bit so they can be useful next time you put the wheel together.