1 1/8" forks in a 1" headttube, have a look at my IS41 adaptor and let me know what you think!

Hi,
regarding putting 1 1/8" forks in a 1" headttube, I have a pretty simple and straightforward adaptor idea (to be machined on my lathe), to accommodate a standard IS41 headset (for example this one) in an old 1" headtube.

This is so simple I am really wondering why no one has done it yet/why this isn't available ready to buy? Yes, space-wise it's getting tight, but it is possible, as a 1 1/8" steerer has a OD of 28.6mm and in my concept I have 28.7mm ID left, i.e. 0.1mm of air (better than nothing ;-). Also, the wall thickness of the adapter will be rather thin at 0.75mm, but this can be resolved by using stainless steel instead of aluminium for the lathe parts.

Check out my drawing here (red = adaptors) and let me know if have missed anything!?

Good luck pressing in a 0.75mm thick cup without deforming it.

Ok well depends a bit on headtube preparation/reaming and of course I could always lower the cup diameter very slightly on the lathe

to be machined on my lathe

Can you make us inverse shims please?

You don’t have 0.1mm clearance, you have 0.05mm maximum if your 2 tubes are exactly concentric. That doesn’t sound like enough to me.

Yes I meant 0.1mm = 2x 0.05mm.
So you mean the steering could seize?

0.05mm doesn't sound like much of gap, there must be tolerances on bearings and deformation in a few places that could eat up .05???
I suppose if you have kit why not try though?
If I had a lathe I'd be knocking out all sorts of stuff!

I am actually considering to simply do external cups, that might make things easier.
Or I stay internal but go down to 0.6 or 0.5mm wall thickness at the internal section

Its gone a tight squeeze.... looking forward to seeing how this pans out.

Take a look at this http://www.global-flat.com/smf/index.php?PHPSESSID=c52edeabbf279a24a787443f4ca239fb&topic=28925.0

@gbj_tester might have a good view

Just wondering what the benefits are? If there isn’t sufficient clearance then steering will probably feel horrible. Potential for component failure is also a concern.

Potential for component failure is also a concern.

Yes, this would worry me. If the insides of the cups get worn away by the steerer then the cups will come adrift. If the steerer get worn down by the cups then it could snap.

Yeah with the amount of loads that go through a steerer, that amount of material will deform pretty sharpish.
I've seen the 'new' threaded BB30 to BSA fail on a few occasions so far; I know the loads aren't proportional, but you get the picture.

tester might have a good view

I don't know whether it's a good view, but I can see a Cane Creek EC34 headset and a set of digital calipers from here, and they tell me that the acceptable numbers are 0.7mm radial clearance and 2mm wall thickness of 6000-series aluminium, the first to avoid interference and the second to avoid shearing the plug off the flange.

2mm is a lot thicker than 0.7mm

Nearly 3x

Maffs

2mm is a lot thicker than 0.7mm

But some steels are a lot stronger than 6000-series aluminium

More than 3×

Matweb

FWIW, when CK/Cielo did this, they brazed the cups onto the ends of the head tube so that the full ID of a 1¼" OD head tub was clear for the passage of a 1⅛" steerer

Magnets.

Even in stainless, 0.75mm is bloody thin for something you'll be trying to press fit into the headtube. And 0.05mm is what I'd consider a loose sliding fit rather than a clearance tolerance. The only way I can see it working well is to make the headset cups totally external and then either bond, braze or weld them to the outside of the headtube. With your design I'd classify the headset cups more as bushings than bearing retainers. Mind you, I've always wondered why headsets don't use bushings rather than bearings. An Igus bushing would be fine for that purpose I'd have thought.

I can see it working another way. 1" fork.