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Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

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Old 06-07-12, 08:12 PM   #1
veryredbike
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Cold setting HT-DT sub assembly

I'm building my bike in sub-assemblies and have the dt-ht bit done... but it's 59.6 degrees instead of 59.2 degrees. In theory, I know I insert some thicker wall tubing down the down tube and head tube and then crank. In practice, I've already sunk some water bottle bolts through the down tube. I decided to give it a shot anyway, and braced the head tube with a scrap piece of tubing and really put some weight on it... and it seemed to move a bit, but when I checked it a few minutes later, it was right back at 59.6. So... do I just push harder? Am I hosed?

I have another set of tubes/lugs coming, but I'm hoping that they're for bike #2 ;-)
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Old 06-07-12, 08:22 PM   #2
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Aaand a tube just buckled. Luckily it was the scrap downtube I was using to brace the head tube... That was a scary feeling! I didn't think about it, but the edge of the head tube was right after the transition to .5 mm. Yowza.
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Old 06-07-12, 09:16 PM   #3
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Stop right now...no more coldsetting for you!
I'd just leave it. You'll never notice a half degree difference when you're riding it and- because this is your first frame- I kinda doubt you'll be able to keep that 59.2 angle after everything else is attached and the fork is built.
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Old 06-07-12, 09:26 PM   #4
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But I want to be a master framebuilder NOW, and make only PERFECT FRAMES! ;-)

Ok, yeah, that's good advice. It hasn't buckled yet, it'll still ride like a bike when it's done, time to stop tempting fate and make peace with the learning curve. Must not let the perfect be the enemy of the good... new life motto.
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Old 06-07-12, 10:11 PM   #5
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I'd go so far as to suggest you mentally note your "failures" that aren't a safety hazard and move on with the build. My first build had too much rake in the fork, and the light bulb didn't come on until I rode it some miles and realized why it felt somewhat twitchy. A number of things weren't awesome, but each attempt gets quite a bit better. I agree with Chauncey. You'd have never noticed an error that small.
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Old 06-07-12, 11:43 PM   #6
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I have never seen anyone cold set that angle. Cold setting is much more effective for errors out of plane. If you get an angle wrong, it's really hard to correct
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Old 06-08-12, 02:33 AM   #7
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Thanks guys, good advice all around. Am I correct in saying that, since the tube shows no sign of buckling, it should still be safe to build up? (I know there are no guarantees, but a "yeah, spent half an hour wrenching on the thing will kill you" or a "eh, probably ok" would be helpful ;-)

Last edited by veryredbike; 06-08-12 at 02:38 AM. Reason: Clarity
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Old 06-08-12, 05:12 AM   #8
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Originally Posted by veryredbike View Post
I'm building my bike in sub-assemblies and have the dt-ht bit done... but it's 59.6 degrees instead of 59.2 degrees.
If all you have is the sub-assembly and the error is killing you, alter the fork length by a mm or two and the lower head angle will change accordingly atmo. PS when we were in London the lower joint was the first one produced. After it was brazed but still red hot, the head tube would be hung over a mandrel and the down tube was tugged up or down to conform to a series of angle templates that were sited against it. Different templates were chosen so that the desired head angle for the particular frame size would ensure that the first braze yielded the desired result. Yes - it was set while the sub-assembly was red hot, right from the firebricks it was brazed against. So very Dickensian.
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Old 06-08-12, 07:21 AM   #9
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Richard, thanks for the reminder that we sometimes over-think things.
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Old 06-08-12, 10:49 AM   #10
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If you already have the fork, you can also also change the design by increasing or lowering the BB. 1/2 degree means about 5 mm of fork or BB height.
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Old 06-08-12, 03:52 PM   #11
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Using a prebuilt fork, but I'll keep that in mind for bike 2. In cold setting in general, if the tubes don't warp or buckle, is it assumed safe? I leaned on it quite a few times and pretty hard, but it looks ok.
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Old 06-08-12, 03:59 PM   #12
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I think the no-buckle rule is about right. I wouldn't worry about it. Most steel frames from pre-heat treat era were cold set.
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Old 06-08-12, 06:26 PM   #13
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Using a prebuilt fork, but I'll keep that in mind for bike 2. In cold setting in general, if the tubes don't warp or buckle, is it assumed safe? I leaned on it quite a few times and pretty hard, but it looks ok.
May I just add that the difference between what was planned and yielded (three tenths of a degree) not only
would be hard to measure, it will be indiscernible on and off the bicycle when ridden AND it (the three tenths...)
would be more if the front and rear tire inflation were not exactly the same, or if one wheel's diameter varied from
the other atmo.
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Old 06-08-12, 06:42 PM   #14
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May I just add that the difference between what was planned and yielded (three tenths of a degree) not only
would be hard to measure, it will be indiscernible on and off the bicycle when ridden AND it (the three tenths...)
would be more if the front and rear tire inflation were not exactly the same, or if one wheel's diameter varied from
the other atmo.
Makes total sense! I got a wixey angle finder thing... sort of precise down to about .1 degree... but you breath on the tube and it changes. I think I've let myself get a bit too focused. Same thing happens for me wheelbuilding; I get focused on the gap and when I pull back a bit, I realize that I'm already way past the point where no one could possibly tell the difference, and have probably been there for some time.
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Old 06-08-12, 08:27 PM   #15
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If you play with it you'll notice the Wixey cube will often give you different results along the same tube. +/- .1 degree means it could be off .2 degrees at any time. Add to that the small size of the Wixey and you see it's just a guide. The tubes themselves don't start perfectly straight, so the lower end of the ST might be 73, while the middle is 73.2, and the top is back to 73.1. You are right veryredbike about being too focused. I think in recent years we all have become slaves to BikeCad drawings with dimensions to the tenth of a degree and mm's in decimals. No frame is as these drawing are conceived. Give 10 guys string and levels and tape measures, and they will all come up with something close but different. I think .2 - .4 degree would be a more reasonable goal given the material we're dealing with.
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Old 06-10-12, 03:25 AM   #16
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If you play with it you'll notice the Wixey cube will often give you different results along the same tube. +/- .1 degree means it could be off .2 degrees at any time. Add to that the small size of the Wixey and you see it's just a guide. The tubes themselves don't start perfectly straight, so the lower end of the ST might be 73, while the middle is 73.2, and the top is back to 73.1. You are right veryredbike about being too focused. I think in recent years we all have become slaves to BikeCad drawings with dimensions to the tenth of a degree and mm's in decimals. No frame is as these drawing are conceived. Give 10 guys string and levels and tape measures, and they will all come up with something close but different. I think .2 - .4 degree would be a more reasonable goal given the material we're dealing with.
I'm no master frame builder, but.....this. If you get the two wheels in line and the angles within a degree, I challenge anyone to discern the difference when riding.

Incidentally, the very first 'real' joint I brazed was a DT/HT assembly, and it was out by a little less than a degree, and I buckled the DT trying to cold set it. I don't think I will ever try that again. My toe still hurts from kicking my workbench after that one.
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