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  1. #1
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    Fillet Noob Question: Head Tube Warp

    After doing a fair amount of practice brazing, I started my first frame this week. The seat tube sleeve went well, as did the ST-BB joint. Little to no warpage on any of it. Then came the HT-DT joint, and I overheated it. The head tube is warped (it is no longer round). At first I couldn't tell for sure, but putting a caliper on it shows that it is slightly ovalized.

    Which brings me to my questions...

    Is ANY head tube warping acceptable?

    If so, how much is OK?

    I'm guessing I can ream it, but again, how much is too much? Are reinforcing rings at the ends of the HT a good idea?

    Thanks for your help!

  2. #2
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    What type of headset are you using?

    If it is the press in type and it is oval by .5mm, I would not worry.

    If your head tube was of the type that requires reaming out to finish fit after welding, then again, no problem as you are addressing the oval as part of the build process.

    The Paragon type of head tube is better than adding reinforcing rings as you still have to put heat on them, and heat is the distorter.

    There is always a risk of distortion at any of the joints. You may need to adjust your technique a little due to the thinner HT as opposed to the thicker walled BB. Its practise and growing experience that improves the joint. I don't think you've destroyed the frame. I have pressed in headsets into frames that were a bit out and have not given any problems when I worked in the LBS. More critical was getting the ball races parallel so the fork turned without binding.

    Hope that reassures you.

    Be good to see some pictures when finished.

    Eric
    If I don't make an attempt, how will I know if it will work?

  3. #3
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    Early on I warped a head tube pretty good, so it's always on my mind while brazing. So much so that I asked Dave Kirk about this at NAHMBS last March, and he suggested putting some flux on the front area of the tube and heating it until it goes clear (up to temp.) The idea is to give the whole diameter pf the tube a chance to move as opposed to just the area being joined, and that allows it to settle back into round. Or something like that.

    You may also need to do a better job of pre-heating all the way around the head tube (or BB shell if you're at that end) which may prevent it altogether.
    Last edited by Smudgemo; 07-23-2012 at 04:09 PM. Reason: Grammar issue from being not fully awake.

  4. #4
    Randomhead
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    you can actually get it to move back to some degree by heating up the front of the head tube now. Doesn't actually have to be all the way up to temp. I don't have a lot of fillet experience, so this is not gospel by any means. But I have played around with witch wanding tubing. It's not an exact science, and you've locked it out of round to some degree by brazing

    I don't see how you can plan on having the headset pull it back round because you are going to have to ream it first. Depends on how much material you have left.

  5. #5
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    I did the same thing on my first frame. I was using the 1.1mm wall head tube that comes with the Nova tube sets. Obviously, with better technique I could have avoided this, but I wish I had known that there were better options out there for beginners - Nova sells a head tube with 1.6mm walls.

    I just peaked at your blog and it looks like your frame has a really long head tube and that you have quite a bit of room between your joints and the ends of the tube. I would guess that as long as the ends of the tube are still round you shouldn't have much trouble after facing. I would shy away from reaming to get the inside back to round. As long as the warp doesn't interfere with your headset cups, or in the case that it's extremely warped, your steerer tube, then any material you remove is just going to weaken the tube.

    If you're obsessed with making the tube round again you might try using a tailpipe expander (Small Tail Pipe Expander) though I don't recommend it. We keep one in the shop to repair the all-too-common "I dropped my new frame on the head tube" accidents. It works well for rounding out the end of a squashed head tube, but I would hesitate to use it anywhere near a joint.

  6. #6
    Nemophilist
    Reputation: TrailMaker's Avatar
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    Hmmm...

    Would I be correct in assuming that the HT is now smaller in diameter from front to back than it is side to side?
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  7. #7
    Randomhead
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    unless something really weird happened, that's the normal distortion

  8. #8
    Nemophilist
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    So;

    Then that is from the filler material shrinking and drawing the sides of the tube back. Is it possible to complete the fillet without this distortion? I might imagine this is a great place for that tack sequence and heat control we hear about.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  9. #9
    Randomhead
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    there is a youtube video of a framebuilder in Japan using heat distortion to align frames. I'm having trouble finding it right now. If you heat up one side of a steel tube, that side will shrink. No filler required. The most common manifestation of this that most builders have run into is rear dropouts being too close together because a bridge was brazed after the rear triangle was complete

  10. #10
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    I'll admit to being newb-ish and the odd distorted head tube. Don't worry too much, get some miles in on this frame and practice some more / have a good excuse to make another at some point.

    I'd avoid reaming huge amounts. If the frame is just for you, then safest option is to use a cheap headset (aluminium cups) and file / shape the cups a bit to roughly match the distortion. This avoids pressing them in with heaps of force in the hope that the headset rounds out the tube (which might also end up in ovalised cups and a binding headset).

    If you look at the head tube side on, you might find the ovalisation is caused by the back of the tube flaring (towards the heat of brazing). This might mean you need a slight chamfer filing on the back of the headset cup.

    The one important bit is to have the end faces parallel (you might find that the whole tube has bowed slightly). This can be fixed if you have access to a reamer that only cuts the faces (not the bore at the same time). Otherwise it needs a milling machine or skilled use of a file to get it parallel.

    None of this is particularly clever or of a suitable standard for a production frame - but it is perfectly safe and functional. It is only a push bike not a jet fighter.....

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