Extending a tube

[batt-man]

if you google "bike steerer tube extender" there are plenty for sale - probably easier / cheaper to just buy something?

At the very least though you can see how other companies make 'em - several seem to just clamp onto the existing tube...

[mattthemuppet]

that's a beautiful Litespeed - I lusted over their mtbs back in the day.

As for worries about stuff breaking - read what I wrote earlier. If the steerer is 20mm too short then the junction would not be between the bearing races that support the fork. It would almost certainly not be between the top race and the stem either as there are very few stems I know of that are 20mm or less in height. It would almost certainly be within the section of steerer clamped by the stem. That's in compressive load from preloading the headset bearings and torsional (leverage?) load from the bars, maybe. There'd be a small risk that the stem would bend the extension off the steerer and I certainly wouldn't do this if I were casing 15ft drops, but as noted above a good shrink fit, loctite and a cross pin should prevent that.

I'm a pretty cautious guy when it comes to modifying bikes as I've eaten dirt (and some pavement) more times than I can remember. Hell, sometimes I can't even remember eating the dirt. I don't think this poses a major safety risk with the above construction.

[754]

I am wondering now the handlebar must go down tube from the top. That would mean any splice would be below that , I am thinking.
depending on clearance, you might be able to run a thin sleeve outside tube for more strength.
I take it it's not being jumped constantly ?

[JRouche]

I have a mountain bike fork that has a steering tube that is short by 20mm. So I plan to lathe up a stepped tube, which I will shrink fit and Loctite into the existing tube.
thanks!

If you have good dental insurance that is the way to go. I would not cause, well fear.

I would not monkey with it if the down tube, or up tube is not mechanically removable from the fork. If it is make a new tube. If its welded sell it. JR

[ezduzit]

Mine's not a mountain bike. And the carbon fork is nothing special. But the rest of the bike frame is titanium and still good shape after 20 years. Perhaps the OP would be willing to post some photos.

[J Tiers]

Such concern over alloy, but not over a Loctite'd connection. That's why I put the winky face.

Ja, well I consider 6061 kinda "squishy" for the usage. But, then, mine is a Lambert, which had aluminum front fork with a steel insert and steering tube, there was a recall to replace the fork, because the dual metal part apparently could fail, faceplanting the rider on the road, among other things (maybe stabbing the rider with the broken ends?). Must have been some cases, mine was OK until replaced. Still have it out in the shed, but would not put it back on the bike.

[ezduzit]

I think the question was strength related...

Such concern over alloy, but not over a Loctite'd connection. That's why I put the winky face.

[J Tiers]

I think the question was strength related, given the particular forces typically applied to a fork steering tube..... which is probably the single most loaded and most critical part on the thing. And the WAY they are applied, which is essentially bending over a "line support".

I am out of the loop on extra-light construction anymore, I assume the fork steering tube is tapered on the ID to put more support at the bottom bending point.

[ezduzit]

Ah , I see that now, at 80 thou wall, do you think it will be 6061 ?

Why not? I've machined 6061 much thinner than 0.08" wall.

[754]

Ah , I see that now, at 80 thou wall, do you think it will be 6061 ?

[ezduzit]

So umm you routinely weld 7075 ?...I do wish the op would give more info...things like diameter , wall thickness...

We regularly weld 6061 aluminum alloy (plus stainless steel), which is what the OP specified in his first post:
"The OD is approx 1.13in and ID is approx 0.96in. The existing material is Aluminum, probably 6061. I plan on using the same."

[754]

So umm you routinely weld 7075 ?
There is likely a safe way to extend it, there area few ways. Some come out, some dont, some are swedged , so machining a new one can be quite time consuming. I do wish the op would give more info and a pic.. things like diameter , wall thickness, wether stem has to fit past the joint.. etc.,

[ezduzit]

Let me guess here, you are not aware that frames have been built and held together by loctite. It a form of bonding construction, it's used in aircraft and other things.. it actually can and does work... i suggested pinning as well in the first post

You guessed wrong.

I have owned a carbon fiber bike whose frame was assembled by gluing CF tubes into aluminum fittings. Of course these bikes ultimately became known for problems with exactly that assembly technique failing. My background is in engineering design, having worked on manned spacecraft projects as well as other aerospace projects. Now I am a boat builder specializing in customizing yachts. And I understand that bonding is sometimes used for such things as assembling the superstructures of yachts to their hulls. Nevertheless, if I am to understand what the OP is trying to accomplish, this is not the kind of application for which I would recommend bonding.

I could safely extend his fork shaft here in my shop because I have a tig welder and lathe with which to do that securely.. The OP has a lathe, but has not mentioned tig welding, which he could easily farm out. Otherwise it would be safer for him to replace the too short fork with a proper one or one which he could easily shorten.

[754]

Not by using Loctite. I'd like to see him do this safely.

Let me guess here, you are not aware that frames have been built and held together by loctite. It a form of bonding construction, it's used in aircraft and other things.. it actually can and does work... i suggested pinning as well in #5 post

[ezduzit]

...some of us here will try to help you bring your idea to a good ending..

Not by using Loctite. I'd like to see him do this safely.