Hi all! Very fresh builder here. I have a head tube that’s fairly oval, about 1mm longer in one direction. I believe the DT mitre was a little deep and the HT conformed to that. Are there ways to round it out? I don’t particularly want to use locktite and would want to avoid brazing an internal ring\sleeve and reaming that out. Thank you all in advance!
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Good question, and I don’t know. The first thing I would do is just press in a headset and see if it was OK anyway– measure how round it is with the headset in there, and also see if the bearings feel OK.
If it turns out the HT is squeezing the cup out of round too much I would try making a cylinder a fraction bigger than a headset but ovalized the other way (just file some kind of flats on it), press that in, bash it out again, and see if you’ve managed to move anything. No idea if this would work.
I’ve also seen it suggested on here that you could put something like JB weld in there and then ream it again.
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Thank you! I’ll definitely give the cylinder a bash, would reheating the HT a little possibly help or would it be too risky?
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Interesting question. My understanding is that increasing temperature doesn’t reduce “elastic strain”, by which I mean the distance something can deform and still spring back.
So if you made the HT hotter it would make it much easier to press things into it. But it wouldn’t make it spring back any less for a given size of insert once you took it out again. So it wouldn’t help unless the thing you were trying to press in was so big you couldn’t get it with the tools you had.
And then there’s the question of how bad the heat cycle is for the tube. I don’t really know. It’s something people mention, but I usually use Reynolds “air-hardening” tubes which are supposed to get stronger if you heat them and let them cool again. Maybe I should do some science experiments with some offcuts one of these days 
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A lot may depend on the size of the head tube and the headset to be fitted.
But I would first try to ream it as and test fit a headset and fork and just see what happens.
If it’s too far out and it’s not gonna work then I would lay some silver brazing in there and ream that out again.
It might be possible to do that with JB weld or similar. But if that failed then you’d end up having to remove it all mechanically I think?
I’d avoid trying to use heat to manipulate the head tube, I’d imagine it would only make things worse.
You’re probably keen to get it built up and ridden but try to take a step back and get it sorted properly now to avoid troubles later.
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Definitely possible, I’ve de-ovalized head tubes and been happy with the results.
Instead of pressing something in, you might try splitting a slightly undersize round insert and driving a shallow wedge in the gap to push out the ovality. Could even use wood, a dowel with a lag screw as the wedge. Start with the insert very close to size and don’t push it past when the head tube shape matches the insert. Reduce the insert’s diameter a bit if it didn’t do enough, repeat until it’s close.
If you get it within a few thousandths / 0.1mm of round, that’s within average-to-better range of a lot of steel production frames.
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HT distortion due to the heating during assemble is not uncommon at all. More time spent heating the DT or TT joint means more time the HT is being heated unevenly, both the DT and TT are on the backside of the H, thus little heat gets placed on the front of the HT. Welding and fillet joining tend to be more likely to distortions than lug joints see.
One way i address this is to heat the HT front side after the DT and TT are done to help even out the distortion. Another is to use a thicker walled HT (oh my gosh, does that mean extra weight). Another is to get faster in your tube to tube joining.
Not mentioned is whether the HT has already been reamed. One could lay in some brass on the HT end’s insides and avoid a full reducing ring and the effort to ream that. Andy
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You could try an expanding mandrel and really crank down on it to get some shape back into it. I have a tool here that I made, not for this particular application, but similar enough that it might work. You only need the ends to be round, so do one end at a time. After I built my tool, someone pointed out that I’d just re-invented an exhaust pipe flare tool, so maybe look at those and see if something like that will work or could be adapted.
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