Front triangle cold setting question

[Mtblucas]

Hi everyone, quick question for you.

I spoke with a machinist today to see about getting some steel rod turned down to the inner diameter of my headtube and downtube. I was planning on using it as a cheater bar to cold set the HT-DT joint after brazing. He quoted me $200 for labor and as a hobbyist that is a little more than I'd like to spend.

I figured I'd first ask around to see how you all cold set a lugged front triangle. For my first frame I didn't even check the angles after brazing. This time around I have a surface plate and am trying to improve this frame's accuracy. If the angle is off by just a couple degrees can you just cold set it without anything in the tubes or would that be too risky?

Thank you in advance for any suggestions.

[jon_norstog]

Matt, if you are trying to get the frame into plane, yeah you can probably do it. First check the BB shell alignment to the seat tube. If they are at 90 degrees, then you can put a long pipe down the seat tube and clamp it really good. If you have some beater headset shells, use them to keep the HT bores round, then put a pipe down the headtube and tweak. You might be able to do this with the frame locked down to your surface plate. Or not.

You may not want to do that with a frame you are selling.

Good luck

jn

[Eric Estlund]

If I'm reading correctly, you are contemplating bending the bike to open or close head and seat tube angles on sub assemblies post brazing? That is a recipe for disaster. I'd recommend looking at your process to braze (your sub assembly or complete front triangle) at the angles you are shooting for.

[Mtblucas]

Hey Jon, that is a good idea to protect the headtube from deforming.

Thanks for the warning Eric. I haven't actually done any brazing on this frame yet so I'll keep the fingers crossed that the angles are spot on after brazing. I was thinking that anytime you heated metal it would always deform requiring some amount of cold setting. It's good to hear that with proper brazing the angle should come out fine.

I remember reading somewhere that the acute angle has more pulling power than the larger angle. When brazing lugs is it best to start on the obtuse angle so the joint is somewhat secure before moving to the acute angle? Am I thinking way too much about this?