Kaisei tubing

[cargonaut]

Howdy framebuilders,
I’m an amateur framebuilder that has built several frames (all for myself) that worked out well for me with non-hardended 9-6-9 cromo tubing. Now I’m considering making for myself a light, springy, fillet brazed rinko bike out of the 7-4-7 Kaisei tubing RH sells which is hardened. While the standard cromo seems to me rather easy to grind, snip, saw, braze, cold set, and file, I assume it will be tougher to do so with the hardened stuff. Any pointers on my new challenge would be appreciated. My approach is using just basic tools since I don’t have any machine shop equipment. Will standard files and tin snips cut it? How is cold setting Kaisei compared to standard cromoly? Is brass fillet brazing okay to do with the Kaisei tubing? Is a 31.7, 1mm wall headtube , fillet brazed (with a reinforcing ring on each end) something that can be considered for a light rider (me, 150lbs)? or is a 32.4, 1.3mm wall head tube a better idea?
thanks,
Drew Devereux

[Andrew R Stewart]

I generally consider a bit thicker wall when filleting a bike. More heat = more distortion. Add time if you're not well skilled with brass fillets and more distortion. I suggest a bit of fillet practice before using the tub set.

BTW in 1982 I made myself the least expensive frame I have ever made. Ishiwata had just come to the USA and was offered at $25 for the complete 022 tube set. Add in recycled bits and a brushed on donated epoxy job I bet the total cost was less than $60. Andy

[Rody]

Drew,

If you are fabricating using mostly hand tools, you will find the experience of working with thin wall, hardened tubing, to be a miserable experience.

To be clear...I'm not saying it cannot be accomplished, but the fun factor is greatly diminished due to the lack of appropriate equipment to manipulate the material to your will.

Rody

[false_aesthetic]

I 2nd what Rody says. But I still went after it. And I'm happy I did.

[steve garro]

It'll work - being thin is in your best interest here - 1/7/1 Supertherm is miserable - I hand mitered 50+ bikes (54 exactly, love my mill)

It's not so much distortion in the tubes but the BB, seat junction and head tube - where the thinness will be most noticeable is in the thick / thin joinery.

K19, I assume?

It's damn nice tubing, I have had Kaisei imported from Japan for my own bikes.
- Garro.

[Jonny Cycles]

While some hardened tubing is miserable to miter with a hacksaw and file, I find the Kaisei tubing is not. I miter it all to time with hacksaw and file, no complaints from me or the files.

Take care when doing the finish work post fillet brazing. 0.7mm doesn't leave a lot of room for undercutting.

[cargonaut]

Thanks very much everybody for the kind replies! I think I will give it a try and then repost on how it went.
Drew Devereux