a Sturmey front X-FD brake hub to 80mm OLN?

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SA_SA_SA
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a Sturmey front X-FD brake hub to 80mm OLN?

Postby SA_SA_SA » 11 Feb 2018, 7:37pm

I have a (discontinued) greenspeed-modified-to-80mm-OLN front SA hub brake* in my folder ----

But given that the standard OLN hub has a large 'waist' I wonder if the greenspeed solution isn't a bit extreme?

Is a DIY version simply by cutting out the waist from a standard X-FD and using (20mm shorter) a non-stepped axle with a sleeve possible?

*http://www.atob.org.uk/bicycle-accessories/brompton-hub-brake/
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Brucey
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Re: a Sturmey front X-FD brake hub to 80mm OLN?

Postby Brucey » 12 Feb 2018, 1:59pm

having given this a little thought I would suggest that the following might be a good route forwards, if you insist on retaining 80mm oln.

1) Bore the hubshell out about another 4mm
2) cut the hubshell in half, trim to length and face the joint
3) bond the hubshell halves back together again, using a ~2mm wall steel tube through the hub centre, bonded in using epoxy

For an axle, you could use the original one, cut in the centre and rewelded to a new length. If you wanted to, you could machine shoulders onto the ends, and again bond the axle together using a steel tube and epoxy. I don't think a shoulderless axle would be ideal because it wouldn't support the bearings correctly and there isn't enough room for two locknuts as would be required for adjustment on a shoulderless axle.

In extremis the epoxy could soften through brake heat. I don't think this will matter in the case of the hub joint (it ain't going anywhere) and in the case of an axle I think that the conditions would need to be extreme before it would become an issue.

Looking at the hub I think you could rob ~5mm each side by just altering the locknuts which means that ~90mm oln is within reach without big mods and 80mm would only require a 10mm cut and shut job on the shell and axle.

cheers
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SA_SA_SA
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Joined: 31 Oct 2009, 1:46pm

Re: a Sturmey front X-FD brake hub to 80mm OLN?

Postby SA_SA_SA » 12 Feb 2018, 5:54pm

Thanks.

I was always puzzled why Brompton never offered such a narrowed hub as an option given that SA make special hub gears for them. It is much nicer and less maintenance than a sidepull caliper..
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SA_SA_SA
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Re: a Sturmey front X-FD brake hub to 80mm OLN?

Postby SA_SA_SA » 13 Feb 2018, 12:54pm

Given that the hub has cartridge bearings:


on the non brake side, the photo shows 2 locknuts, but is that really necessary?
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Brucey
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Re: a Sturmey front X-FD brake hub to 80mm OLN?

Postby Brucey » 13 Feb 2018, 2:21pm

the standard configuration outside of the bearing on the RHS is a dust shield (much thicker than it needs to be) a spacer and then a locknut.

The locknut doesn't do much; everything is just fine even if it is only finger tight; once the wheel is in the frame the track nut load clamps the spacers etc and the bearing against the axle shoulder.

cheers
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[XAP]Bob
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Re: a Sturmey front X-FD brake hub to 80mm OLN?

Postby [XAP]Bob » 13 Feb 2018, 2:53pm

Brucey wrote:Looking at the hub I think you could rob ~5mm each side by just altering the locknuts which means that ~90mm oln is within reach without big mods and 80mm would only require a 10mm cut and shut job on the shell and axle.


Does a 'shorter' cut and shut actually offer any advantage over a wider one though?
A shortcut has to be a challenge, otherwise it would just be the way.
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Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: a Sturmey front X-FD brake hub to 80mm OLN?

Postby Brucey » 13 Feb 2018, 2:55pm

yes, the wheel is stronger because the flanges are further apart. There is also less machining required in the central barrel OD area to get a nice blending on the radius at the join.

cheers
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SA_SA_SA
Posts: 1577
Joined: 31 Oct 2009, 1:46pm

Re: a Sturmey front X-FD brake hub to 80mm OLN?

Postby SA_SA_SA » 13 Feb 2018, 5:00pm

[XAP]Bob wrote:
...I think you could rob ~Xmm each side by just altering the locknuts ....

Does a 'shorter' cut and shut actually offer any advantage over a wider one though?

If the shorter cut == no cut and forks were springy enough then the advantage might be no machining necessary... :)
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