Custom rear bearing spacer.

[TiAvenger]

I got the bearings and spacers out of my SC spokes and low and behold, the 17mm spacer is about 8mm too thick to go in the rims. 
Not only that, the spacer "channels" inside the hub are aluminum, and I fear the 17mm spacer would damage them due to only having about 3 mm of contact at each end, vs the 25mm solid shaft.  Rather than mill out the channels (which would be very easy to screw up,) it looks like I will have to have a custom spacer made.

Question is, what material will be best for the task?  Both current spacers are steel(?), but to do a solid steel would add a bunch of unwanted weight.

So, what should it be?

Steel?

Aluminum?

Titanium?

Other?

[Smokescreen]

Aluminum is the easy answer here.  You are talking about spacers on a double sided I assume?  Aluminum would be the easier to machine, and since your wheels/hubs are aluminum, you won't get contact oxidation like you will with steel.  Ti is too pricey and won't really offer weight savings over aluminum, and considering the price difference, if you get the machining wrong on the first go, you can afford to do again with alu.

[TiAvenger]

Aluminum is the easy answer here.  You are talking about spacers on a double sided I assume?  Aluminum would be the easier to machine, and since your wheels/hubs are aluminum, you won't get contact oxidation like you will with steel.  Ti is too pricey and won't really offer weight savings over aluminum, and considering the price difference, if you get the machining wrong on the first go, you can afford to do again with alu.

The only concern I have with Aluminum, is that both stock ones are steel, why didn't Ducati use Al for stock?  The price difference is not that much, will the inner bearing races damage the spacer upon installation? 

The Ti stock needed would be 300 bucks.  so that's out

Im leaning towards  some 2024 if it turns out it will be strong enough

[TiAvenger]

what about magnesium?

[aaronb]

steel was probably used to prevent corrosion, otherwise aluminum and some anti-seize would be fine. 

[TiAvenger]

Ok here is what everything looks like

On the left is the stock SC spacer, (25mm) on the right is the (17 mm) conversion spacer(which wont work)




Length difference




Width Difference



Interior of hub

[Speeddog]

The flanges on each end of the 17mm axle spacer are to keep the spacer from falling out of alignment when you take the axle out.
When the axle is in, the flanges don't touch anything.

Easiest route is a spacer with the same OD and length as the 25mm spacer, and the same ID as the 17mm spacer.

2024-T6 is strong enough.
You could use 6061-T6 as well, might be easier to get or cheaper.

IMO, Ducati used steel because it's cheaper.

[TiAvenger]

The flanges on each end of the 17mm axle spacer are to keep the spacer from falling out of alignment when you take the axle out.
When the axle is in, the flanges don't touch anything.

Easiest route is a spacer with the same OD and length as the 25mm spacer, and the same ID as the 17mm spacer.

2024-T6 is strong enough.
You could use 6061-T6 as well, might be easier to get or cheaper.

IMO, Ducati used steel because it's cheaper.

I did the math and 7075 is around 230 g vs the stock steel at 302 g.

And that's a solid "pipe" design 32mm outer diameter and 18mm inner.

My only question is, will there be a wear issue or damage issue when the bearings are inserted?

Also, does the spacer rotate with the wheel?  I would assume it does.

[Speeddog]

No, there's no wear or damage issue if you get the length of the new spacer the same as the 25mm spacer.

The spacer does not rotate, it's clamped by the axle when you tighten the nut.

You may need to chamfer the OD of the ends of your new spacer so they don't drag on the seals of the bearings.

The thickness of the bearings may be an issue for general fitment, as AFAIK bearings with a 17mm ID and same OD as the 25mm ID bearings will be thicker.

[TiAvenger]

No, there's no wear or damage issue if you get the length of the new spacer the same as the 25mm spacer.

The spacer does not rotate, it's clamped by the axle when you tighten the nut.

You may need to chamfer the OD of the ends of your new spacer so they don't drag on the seals of the bearings.

The thickness of the bearings may be an issue for general fitment, as AFAIK bearings with a 17mm ID and same OD as the 25mm ID bearings will be thicker.

Yep they are 2mm thicker, the hub will be machined out to accompany them. Which means I will have to shorten the spacer by the same amount, I assume.

Also taking rough measuements (my calipers were lost in the move) It seems that the ID is about 1mm larger than the corresponding axle, I assume I should keep that gap? (once properly measured.)

And how tight of tolerances would you think? .01, .001, .0001mm?

[Speeddog]

IMO, don't machine the hubs.

Make a stepped spacer, kinda like this:

                       _______________________
       _________|                                       |_____________
      |______________________________________________|


      _______________________________________________
      |_________                                        ______________|                                                                               
                       |______________________|

Same ID as the 17mm spacer.
Major OD same as the OD of the 25mm spacer.
Length of the major OD portion same as the length of the 25mm spacer.
OD and length of the smaller ends to fit the ID and width of the 25mm bearings.

There's also the caliper bracket to consider, as well as the sprocket carrier....

This is a fairly involved deal, nearly impossible to get everything right via the internet....
Wanna give me a call?

[TiAvenger]

So basically run 25mm bearings with the spacer carrying the axle through them?

The only component I don't have right now is the brake (caliper assembly/bracket)

Stu thinks the hub will have to be machined anyway to accept that. No way of knowing till I get it from Joels.

I was just pre planning so when the rest of the bike arrives, I can hit the ground running.

Red= axle  Blue = spacer Black = bearings Green= hub  note, not to scale.

[Speeddog]

So basically run 25mm bearings with the spacer carrying the axle through them?

Yes.

Trouble is, I don't know what the rest of the parts are like, so going that route may make other stuff more complicated.

The only component I don't have right now is the brake (caliper assembly/bracket)

Stu thinks the hub will have to be machined anyway to accept that. No way of knowing till I get it from Joels.

I was just pre planning so when the rest of the bike arrives, I can hit the ground running.

I would avoid machining the hub unless you *absolutely* had to.

And how tight of tolerances would you think? .01, .001, .0001mm?

Are you going to be making the spacer yourself?
Tolerances will vary depending on which area of the part you're talking about.

[TiAvenger]

Yes.

Trouble is, I don't know what the rest of the parts are like, so going that route may make other stuff more complicated.


I would avoid machining the hub unless you *absolutely* had to.


Are you going to be making the spacer yourself?
Tolerances will vary depending on which area of the part you're talking about.

Possibly, its a fairly simple shape my main concern is drilling the ID on the lathe.

A local machine shop charges 72 an hour, no minimum.

I would rather not machine the wheel as well.

Did you catch the drawing? Is that what you are thinking?

[Speeddog]

Yeah, your drawing is conceptually correct.
The length of the 25mm OD areas may need to be different, depending on the sprocket carrier and caliper bracket.

If your lathe is in good condition, and of sufficient size, and you've got good tooling, the center hole is do-able.

Maybe cheaper in the long run to have the shop do it, depending on how you look at it.
Talk it over with them, see how much they think it'll be.
Depending on their machines and tooling, it may be reasonable cost.