HT angle changing after brazing

[BigPoser]

Master Builders!

I've been building some practice frames and after getting the front triangle all brazed up I noticed that the HT angle changed. The first one changed by 0.7 degrees from 72* to 72.7*. The second changed from 72* to 72.5*. Both frames had extremely tight miters and the alignment was spot on after tacking as well. I've not encountered this before in any of my previous frames to date and I'm racking my brain trying to figure out how this happened. My current thought is that either I'm not using enough heat, and because of this I'm spending too much time brazing the HT/DT joint, or, I'm using too much heat.

I start at the DT/HT joint and braze 90* around the joint, then move to the opposite 90 diagonally across, then the third 90, and finally the last.

I've timed myself and I'm sitting around 5 minutes per joint, but due to the extra bronze on the underside of the DT/HT, I'm at about 8 minutes at this joint. That needs to come down no doubt.

What exactly could be happening to cause that much movement?

Any and all thoughts and advice is welcomed.

Thanks.

Brandon

[BigPoser]

Bueller......

[e-RICHIE]

These triangles are being brazed while in a fixture, or held freely in space?

If it's a lugless assembly, or even if it isn't, and you *want* to buy back that missing .7 of a degree, simply add a millimeter or too to your fork span.

Or, next time - assuming this is a trend - don't trim the bottom of the head tube and leave it long a bit. That'll get you the same result as a longer fork.

[Curt Goodrich]

This isn’t a snarky question. How do you know the angle changed?

[BigPoser]

This isn’t a snarky question. How do you know the angle changed?

No worries. I know it changed because I put it back in the fixture to get some CS's on it and the HT wouldn't fit back in it. I had to adjust the cups to fit correctly and then measured the new angle.

I haven't seen this happen before which has me perplexed. I "think" I know what happened but not 100% positive.

[e-RICHIE]

so the head tube angle increased but nothing on the rest of the frame went with it?

i'm going to suggest you lean the frame back in the refixture process, essentially create the angle you want, have the top tube raise a red hair or three, and move the saddle forward .6466464 millimeter to adjust for the revised setback that results.

[BigPoser]

These triangles are being brazed while in a fixture, or held freely in space?

If it's a lugless assembly, or even if it isn't, and you *want* to buy back that missing .7 of a degree, simply add a millimeter or too to your fork span.

Or, next time - assuming this is a trend - don't trim the bottom of the head tube and leave it long a bit. That'll get you the same result as a longer fork.

Good questions. Let me answer. The frame was only tacked in the fixture and brazed in free space. I used a Paragon HT that I had and really can't leave it longer to "raise" the front end up to slacken out the angle.