Reinforcing a fork steerer

[jim g]

I haven't been active on the internet-bob list for at least a decade, but on a whim, I poked around in the list archives yesterday and discovered an old thread from 2023 about defective Kogswell forks.  Apparently the original report was on the Paceline forum which you need to be subscribed to in order to view photos.  I found a post referencing the original on the UK Cycling Forum which looks to be publicly viewable.

At any rate, it looks like some of the 1-inch Kogswell forks were made using an LC44 1-1/8" crown that was shimmed down to accept a 1" steerer.  This, in itself, maybe isn't problematic, though it does seem to be a hack.  The issue is that the steerer tube they used is straight gauge with a 1.5mm wall thickness, which apparently isn't thick enough for the stresses at the crown end.

I have two of these forks.  One is on my commuter bike that has a front porteur rack, the other was on my (now retired) Trek 650B conversion rando bike.  Fortunately neither has failed (yet), but I'm alarmed.  I'm wondering whether it'd be worthwhile to reinforce the crown-end of the steerer tube with some sort of press-fit plug, either turned from aluminum or steel.  Or, should I cut off the steerer, grind out the crown, and silver-braze a new steerer in place?  Looking for advice from the experienced collective!

Thanks!

-Jim G in SF

[Travis Ruth]

Yo Jim G,

I've seen some discussion about an insert.

I think you should just make some new forks!

Travis

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[Mark Bulgier]

I haven't seen one of those in person but I think I remember that the steerer wasn't shimmed, it was bulged out to fit the crown.  Which probably thinned it.  Super-sketchy idea, bordering on criminal negligence if you ask me.  So a reinforcement would have to have a complex shape with two diameters and a transition between them to mimic the inside shape of the bulged steerer.  Examine your forks closely, dunno if that's true, but the reinforcement idea might be non-trivial. 

Is the ID of the steerer at the bottom 1.0" or smaller?  If so then maybe putting a new 1" steerer in there is do-able.  But you said 1.5 mm wall, which would make the ID a bit over 1.0", so you'd be "reaming air".

When making the hole in the crown to replace a steerer, precision is needed or the fork will be out of alignment after brazing.  A slight angular error gets magnified by the time you get down to the tips, tho maybe still within the amount you could fix by cold-setting.

For years now I've been thinking of making a fixture to bore the crown for steerer replacement on the lathe.  It would look like a fork brazing jig, with a dummy axle holding the dropouts, but it needs some way to rigidly clamp the crown.  Aligning on X is easy with the cross slide, but aligning in Y (up/down) will be trickier, possibly by shimming.  It'll be different for each fork.  Making such a fixture just to do one fork doesn't make sense though.

[Jon Norstog]

That would just be too easy and cost-efficient.

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[jim g]

On Wed, Sep 3, 2025 at 10:54 AM Mark Bulgier <Ma...@bulgier.net> wrote:

I haven't seen one of those in person but I think I remember that the steerer wasn't shimmed, it was bulged out to fit the crown.  Which probably thinned it.  

I did read this in the original discussion, and tried to inspect my fork as such.  On my fork, the 1" steerer has a top ID of about 22mm, and also about 22mm at the crown end.  It's hard to view up inside the steerer from the crown end since there is a fender-mounting tab brazed in place.  Fortunately I don't have a star nut in the other end, so I was able to shine a flashlight down inside and it looks to me that the ID is constant the whole way down the tube.  I am willing to remove the fender-mount tab on the other end to better inspect things and see whether the steerer tube was bulged to fit the 1-1/8" crown -- I will do that this weekend.

 

 (photo credit -- Joe Bunik)

Is the ID of the steerer at the bottom 1.0" or smaller?  If so then maybe putting a new 1" steerer in there is do-able.  But you said 1.5 mm wall, which would make the ID a bit over 1.0", so you'd be "reaming air".

As I said, I'm getting about 22mm [.882"] ID at the crown end of the steerer.

 

For years now I've been thinking of making a fixture to bore the crown for steerer replacement on the lathe.  It would look like a fork brazing jig, with a dummy axle holding the dropouts, but it needs some way to rigidly clamp the crown.  Aligning on X is easy with the cross slide, but aligning in Y (up/down) will be trickier, possibly by shimming.  It'll be different for each fork.  Making such a fixture just to do one fork doesn't make sense though.

That is a brilliant idea.  It also made me remember that we've got a big ol' horizontal mill at work (Lagun), which might be easier to do a one-off set up for a job like this.

 

Thanks!

-Jim G

[Eric Keller]

Looks like that fork was made properly. Measure the OD of the steerer under the crown to make sure it is 1" diameter. If it's 1 1/8", I wouldn't ride it. I recall that once forks started breaking in half, the contractor (Maxway?) started making them with the proper parts. 

Eric Keller

Boalsburg, Pennsylvania

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[Hahn Rossman]

I'd be more concerned about the tack welding, then brazing! I don't know how that's possible with flux and of they didn't use any...?

Hahn Rossman 

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[Mark Bulgier]

Yeah I've seen various frames and forks TIG tacked and then brazed, it gives me the heebie-jeebies.  Sometimes inside a lug-style BB shell. 

Regardless of whether it makes a strong-enough joint,  it extra-hard to sweat the joint apart when doing a repair.  If you heat it up expecting the joint to come apart, then heat it more, then heat it more, still not coming apart... the frame is ruined unless you happen to notice the TIG tack.  There oughtta be a law!

I had a co-worker who tried that, TIG tacked then dipped the joint in flux and brazed. Not on a frame for a customer, just testing. He was a "git 'er done" kinda guy.  Everyone else in the shop (me included) thought it was sketchy or worse.  I know it's done in factories on low-end frames, but blasphemy in a high-end custom shop.

Am I being too "precious" about it, or is this really a terrible way to make a fork?  Rhetorical question. I've already said those Maxway forks were criminal.

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[Steven Shand]

I've built hundreds of frames that were tig tacked before brazing (not lugs!). It was in a more production-based setting admittedly but these were top-end frames. Cutting samples apart showed perfectly acceptable internal fillets. Flux will get in there if you use enough on the outside. I think the heat draws it in?

It's a quick and efficient way of tacking frames. Having a nice clean batch of frames to work on without having flux all over the place is much nicer.

If you're just doing one frame at a time and brazing straight after then it's probably an unnecessary step.

I understand the concern of not knowing a tig tack is there when doing a repair but I don't think heating a whole fillet brazed joint up to a temp that allows you to pull it apart is a good practice. Again silvered lugs might be an exception there.

Steven

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[Mark Bulgier]

Steven Shand wrote:

I've built hundreds of frames that were tig tacked before brazing (not lugs!). It was in a more production-based setting admittedly but these were top-end frames. Cutting samples apart showed perfectly acceptable internal fillets. Flux will get in there if you use enough on the outside. I think the heat draws it in?

It's a quick and efficient way of tacking frames. 

Oh yeah, for lugless, totally fine.  I've done tons that way too.  We're just talking about a capillary joint like a lug, or specifically in this thread, a fork crown.  Still do-able, but it bugs me a bit.  Maybe I'm just being OCD.

[Jon Norstog]

IIRC Tom Ritchey used to use a combination of TIG welding and fillet brazing on his high-end bikes. 

jn

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[Chapman Cycles]

Hi all,

About 10 years ago, I made a crude attachment that mounted in an Aloris style type clamp on my lather to bore out a crookedly threaded steerer. I centered it on some bar in the 3-jaw and then bored it with an endmill with some hand reaming after that. It was still tedious but saved a bit of time. The Aloris style allowed it to move in the y-axis. 

This doesn't get to the original question though. If it were my fork, I was riding it on the regular, and I didn't want to botch the paint, the Yankee in me would remove that fender mount, hone the inside, and liberally JB Weld a 2-3 inch chromoly steel 7/8"x.058" insert in there. 12 hours later I would drill the fork crown for a standard Daruma style fender mount for extra peace of mind. I would ride that forever. But maybe I'm alone in that? Haha. Good luck, Jim!

Cheers, 

Brian
Pawtuxet Village, RI