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Wheelbuilders! Anyone ever build an eccentric wheel?

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Wheelbuilders! Anyone ever build an eccentric wheel?

Old 03-22-13, 12:00 AM
  #1  
Gnarboots
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Wheelbuilders! Anyone ever build an eccentric wheel?

Like, not a regular, functional bike wheel with an eccentric hub, but a wheel with the hub itself OFF-CENTER. Indeed, a total novelty item, but I was recently asked if I could build one, and after having built hundreds of standard wheels (in all manner of lacing-pattern), I can't even conceive as to figure spoke lengths on an eccentric wheel!!! Any leads?
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Old 03-22-13, 12:28 AM
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This should be interesting. I'm sure some of the geometry gurus out there will have a formula. Like you I've built many "concentric" wheels but never one with an offset hub.

At first thought my approach would be to do a drawing. First- (hopefully) you know the spoke length with the hub centered. Assume the hub is offset 10mm to one direction. So, one spoke would be 10mm longer, and the opposing one 10mm shorter. I'd do my drawing to reflect this and measure each spoke location shown on the drawing.
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Old 03-22-13, 02:18 AM
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It's a pain. A total, major, wriggle-on-the-floor-kicking-your-heels-tearing-at your-hair kind of frustration.
I suppose it'd be possible to map it out and establish a chart for each and every one of the separate spoke lengths needed, and their exact location in the pattern -but I don't have the maths/programming skills for that.
Or if you have your own spoke threading machine, throw the wheel together using only a few choice spokes, then take your measurements from there and cut the remaining spokes one by one.

A far easier option is to make a set of flange adapters. Cut a circular plate out of sheet metal, drill spoke holes at the edge. Then cut an offset hole in the plate and mount the plate to the spoke flange of the hub.
Apart from sourcing the appropriate spoke length (they might get real short if you want a big offset), it's all readily doable with almost no cussing.
Choose the diameter of the plate right, and you can scavenge the spokes out of a kid's bike.
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Old 03-22-13, 04:21 AM
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Ever build an eccentric wheel?
Not on purpose.
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Old 03-22-13, 06:12 AM
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I might have known. After crafting the response below I decided to search for build eccentric bicycle wheel and found this:
https://www.bikeforest.com/CAD/hulaCAD.html.
You can configure variables and then obtain exact length and position for each spoke. Just goes to show you - Google first, ask questions later.

Yes, I built a set for a clown back in the 70's. No computers then, and even now calculating spoke length would be quite a challenge. I recall figuring the amount of eccentricity that would pass through the fork/triangle, chose a cross pattern that was appropriate for the longest spokes I had available, and then set the first two spokes. I set up a table so that the rim was supported well on two sides and the hub clamped upright, flanges centered on the rim. I used long spoke nipples to give me more leeway and just fit each spoke as I went. As difficult as it is already there is no way this would be practical outside of a shop, professional wheel builder or access to a spoke cut/thread machine.

Using a radial pattern on the front would enable one to manage a formula for spoke length reasonably well with proper knowledge of geometry, but I don't want to see if I'm capable of figuring it out for a laced wheel.
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Old 03-22-13, 06:30 AM
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The original pattern Pedersen three-speed hub [1903(?)-1907] had pear shaped flanges and required twelve different spoke lengths to build a circular wheel. Later models had the off-center gear cluster within circular high flanges.
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Old 03-22-13, 06:44 AM
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All driven by ERD's...

My initial assessment though is tension is going to be fun...will probably want to keep a "glue" handy just in case.

=8-)
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Old 03-22-13, 07:51 AM
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Originally Posted by Dan Burkhart View Post
Ever build an eccentric wheel?
Not on purpose.
That's what I was thinking too.
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Old 03-22-13, 08:10 AM
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Old 03-22-13, 09:38 AM
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Originally Posted by Gnarboots View Post
Like, not a regular, functional bike wheel with an eccentric hub, but a wheel with the hub itself OFF-CENTER. Indeed, a total novelty item, but I was recently asked if I could build one, and after having built hundreds of standard wheels (in all manner of lacing-pattern), I can't even conceive as to figure spoke lengths on an eccentric wheel!!! Any leads?
[edited; I may have mis-understood that you were going for a ellipitical rim... apologies but the model still would work when it comes to buying a box of spokes for each mm length from min to max... /K]

Gnar; This is rather simple. Seems obvious

1) Measure the rim diameter at the largest point
2) Measure the rim diameter at the smallest point
3) Calculate the required spoke length for those two sizes
4) Buy as box of spokes for each plus a small box for all the intermediate sizes
4) Begin the build, changing the spoke length gradually as you go.
5) Expect to find a few spokes needing to be changed up or down a millimeter to be able to tension

Seems obvious that you should also use an ellipitical crankset, maybe an offset seatpost, a fork with an unusual bend (the old Continental bend would look odd/wierd enough today).

Sounds like fun project (but generally useless) at the risk of others wanting to clone it for the coolness.
/k
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Old 03-22-13, 10:23 AM
  #11  
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Here's a pair of rather eccentric wheels for you...

https://www.maa.org/mathland/mathtrek_04_05_04.html
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Old 03-22-13, 10:25 AM
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Chuck Kinney was a clown in Ashland for years and rode a fixie, no handed, facing aft. As he zigged and zagged back and forth through the 4th of July parades (and road apples) the wheels would go in and out of sync so his rising and falling varied. It looked like fun. I have speculated for a long time on building such wheels and always assumed that tension in this case would be less of an issue due to very limited, low impact mileage?
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Old 03-22-13, 10:41 AM
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I'd eyeball it with a spoke threading tool and a dremel to grind the spoke down once it was in place.
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Old 03-22-13, 02:48 PM
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I've had a few clowns ask me to build them such wheels. The ride is pretty cool as you can pump the bike in rhythm with the wheels to provide the forward propulsion. The Ingos from the 1930s used this concept on the rear wheel. Watching an old video of Ingos racing is comical.. Years ago I was attending the Chicago Bike Show (out West of the city) and came across an Asian booth with a scooter using this design, just like a small Ingo. As much as i tried to explain that his design was a copy of the Ingo he wasn't able to understand and continued to claim he "invented" the design. Andy.
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Old 03-22-13, 04:00 PM
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It's actually fairly easy, especially if building radial.

You might want to start with a full size tracing of the rim on a sheet of cardboard (side of a bike box) Then draw a circle representing the hub (spoke hole diameter) where you want it located, and measure the distances, hub to rim for the various spokes. Don't forget to compensate for the difference between the rim's tracing and the ERD you would have entered.

Then add 1mm for each 10mm of ctf distance, to compensate for the conic angle.

Crossed spokes can be done the same way, but you measure from the rim to the place the spoke meets the hub (divide the circle for spoke holes, and count back according to cross pattern).

Aligning is the trickier part. When I built one many years ago, I aligned via a shadow projected from a narrow beam light source. Today, I'd mount a laser pointer on the truing stand base and use that as mu reference for side to side. You can't align for hop because it's constantly changing, but a reasonable feel for spoke tension will assure that the rim stays reasonably circular. Or you can tape a deep section rim loosely to your rim, and use that as a template.
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Old 03-22-13, 04:07 PM
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..or you could just use the online calculator I linked to above. I actually don't remember how I did the truing on the two I built - that was over 35 years ago.
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Don't tell me what "should" be - either it is, it isn't, or do something about it.

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