carbonfiber hub/spoke assy for standard rims

[kenkad]

Hello,
Has anyone on this forum attempted to make a carbon fiber hub/spoke assembly that can have a standard bicycle or motorcycle rim attached to the assembly?

I will try to explain one possible process. For example, I can take a reasonably low cost Sette disk brake style hub (number of spoke holes does not matter at this point) as the starting point.
1. Now I make two circular flanges designed so their inside surfaces are machined to fit exactly on the section centerline of the spoke flanges (half of the spoke flange is exposed to the inside of the hub). These circular flanges,clamped with a center bolt, allow me to sand blast the inner surface (between the two flanges and the inside of the flanges) of the hub.
2. Using the 3M AC130 adhesive primer (developed for the aerospace industry), the sandblasted part of the hub is treated.
3. Carbon fiber is then laid into the inner surface to some adequate thickness (maybe 3/16 to 1/4 inch) and cured.
4. Then, using a accurate special arbor, the hub with the carbon fiber is machined in a lathe to create an accurate carbon fiber band (in the center of the hub) for attaching the four carbon fiber spokes.
5. Assume I have a CNC Router fabricated mold, I can place the modified hub into the mold and layup the carbon fiber spokes.
6. The carbon fiber spokes (the correct length for the selected rim) are fabricated and become integral with the modified hub. The spoke mold insert is some form of tapered rectangle, and, accurately molded using some type of heavy duty balloon internal bladder.
7. A accurate template is used to place the typical spoke location mounting holes in the ends of the spokes, using two spoke holes per spoke. Some type of threaded insert would need to be placed in these carbon fiber spoke holes.
8. To prevent galvanic action between the carbon fiber spoke end and the aluminum rim, a thin plastic washer/shim is used. I expect that not every rim is exactly the same size so the shims are needed anyway.
9. MT style rims are necessary because they have a flat inner surface for the spokes to mount against (whether bicycle or motorcycle type rims).

Would there be any interest in this type of carbon fiber/aluminum rim combination for most likely three wheeled vehicles. If we can get a few individuals interested that have 3D CAD experience and carbon fiber fabrication experience, this could be a worthwhile project for the community to possibly learn from.
Kenkad

 

[Drunkskunk]

Its an interesting idea, but I see 2 glaring problems:

1) Spoked rims were never designed to take a load that way. without the spokes to distribute the load, a normal rim would likely collapse on the first hard bump. A Deep V rim designed for a 4 spoke wheel would be needed. and would be strongest/lightest if built as a single piece with the spokes.
1.b) Spoked rims are rarely perfectly straight when unlaced. They used the spoke tension to pull them straight. Without laced spokes, they will likely end up wavey and egg shaped.

2) Bonding the CF spokes to the hub would create a weak point, especialy during side loading and braking. If you want a spoked wheel, its best to mold a CF hub into the spokes, and use an insert to support the bearings.

You would also have a unique engineering problem with adding a disk brake. A disk brake puts all the stopping stress on the spokes. Most carbon spoked wheels avoid that by use of a rim brake.

 

[kenkad]

Drunkskunk,
With regard to your point #2, the aerospace industry uses the procedure I outline in my #1-#4 to bond CF to aluminum. I have essentially created the hub you refer to and, since I have a machine shop, it is far cheaper to use a low Cost Sette hub as I mentioned (I have used these many times before) than to try to machine a new hub with disk brake mounting hardware. I will stick with disk brakes and you can stick with rim brakes.

In regard to the rims attached to the CF spokes, I did not specify the size of the spokes (I only said a tapered rectangle) but I already have the rims. I do not know your definition of 'bump', but this is not for rough trail riding on rocks, etc.

To me, this is an interesting design idea. A glaring problem, only if you have already tried it and can show us your result. If 3D CAD could do a CF FEA analysis, I would do it. I was just wondering if anyone else was interested in the concept. This is not a sales dangler. I do not need the business.
kenkad

 

[Thud]

Ken,
I am lousy at visulising your described item....not familure with the mentioned hub...i believe that skunk was refering to a standard bicycle hoop rim prior to lacing them up.

A typicle rim (bicycle or motorcycle) can be quite egg shaped before lacing with spokes & truing.
I have a mold made for 3 spoke carbon wheels i intended to bond to a standard 20" alloy hoop.....but its another on a list of projects i have on the shelf waiting for more time.

For sure I wish we had dedicated to Solidworks a couple years back at the shop. FEA was my primary interest....but it wasn't my money on the line...& we never got it fully integrated...& haven't renewed the subscriptions.

 

[kenkad]

Thud,
Thank you for the response.

I get drunkskunk's comments. I am constantly involved with advanced students on special projects. I was simply suggesting that it would be good to have two, three, or four people working together so we could share ideas. I want to work with those individuals that want to try new ideas (that is what I tell my students). That is how we learn. If someone has already tried the idea, I would like to know fully what problems were encountered. It is never appropriate to tear down any idea with out having something to substitute, not just words. I teach my students never to open their mouth in criticism unless they first have something positive to say about someone's idea. I expect that on this forum as well. So much for the rant.

I already did this experiment with 16 gauge sheet metal solid spokes. I was not fully satisfied with the attachment methodology at the hub. I can more easily reinforce the CF at the hub. To make the hoop (rim) out of CF as well is not a good idea as far as I am concerned because it would be much harder to make such an accurate mold. There is a Youtube video showing the fabrication of CF wheels and it is very complicated and the molds that are used are very expensive. I can do this mold on a large format CNC router I have. I would put the mold on a 1/2 inch AL flat plate that is large enough so I can use it as the assembly fixture when I attach the rim to the spoke assembly (controlling out of round issue). The spacers I suggested will allow the truing of the rim (wobble issue). I also know from experience that the spoke hole protrusion has to be carefully ground flat to fit properly to the spoke ends, especially motorcycle rims. It may be possible to create a special spacer that would work for deep V rim profiles. I will see if this is feasible.

I hope you get to your three spoke CF rims sometime in the future. I will do up all of the 3D CAD for this, but, I will not post them unless we can get other individuals actually involved and not just talking. In case someone is wondering why four spokes? Very simple to me. The CNC router works more accurately if the spokes are aligned with X and Y, else there is a great deal of interpolation. Thought I would answer that question in advance.
kenkad

 

[Hillhater]

As an engineering /manufacturing exercise i can see some merit in advancing the understanding of CF applications.
But exactly what problems is it you are trying to resolve by producing this hybrid wheel ?
You are using an existing alloy hub and rim, then adapting them to siut a "custom" CF spoke system...why ?
There are already proven CF spokes that could be used
What are the benefits of your proposal.
I have to agree with Drunkskunk, ...that you seem to ignore the effect that multiple, angled, tensioned spokes, have on a rims strength and on the wheels overall ability to adsorb both radial and horizontal loads and transmit torque loads .

 

[-dg]

But exactly what problems is it you are trying to resolve by producing this hybrid wheel ?
You are using an existing alloy hub and rim, then adapting them to siut a "custom" CF spoke system...why ?
...
I have to agree with Drunkskunk, ...that you seem to ignore the effect that multiple, angled, tensioned spokes, have on a rims strength and on the wheels overall ability to adsorb both radial and horizontal loads and transmit torque loads .

+1 on both of these points.

Very few normal bicycle rims are going to tolerate being used this way. They don't have enough lateral strength without the spoke bracing.

Also, how do you plan to tension this wheel? How do you plan to true it? What about fatigue lifetime on both the spokes, and on the unsupported rim which will be experience much larger strains than the designer anticipated?