Seat tube distortion...

[steve garro]

Classic thread........

1: FNG asks question that's been asked 10000000 times before

2: professional builder(s) tell them the truth

3: FNG gets butt-hurt, believes truth does not apply to them.

4: People with slightly more experience (maybe) spew all kinds of hypothetical "answers" thereby clouding the waters when actual answer has been revealed.

5: Tempers flare out of control over the truth

6: Thread is locked.

7: REPEAT












- Garro.

[EricKeller]

every time I see a discussion of this, I think back to my tandem. I'm lucky either seatpost fits. The only examples I had seen were some Jack Taylors and Paramounts, and they didn't use a sleeve on their seatposts. No internet back in 1980 and I didn't even have access to a reamer.

[Will Neide]

OP, are you sufficiently pre-heating the entire area, or just jumping right in? I personally like sleeves instead of externally butted tubes when given the option.

[shirk]

Curious what seat tube you are using in interest of wall thickness comparison to the rest of the options and or seat sleeve.

[phutphutend]

Thanks for all the replies.

Looks like a sleeve (and some practice) is my best bet. But unfortunately my lathe I'd not up.to turning these myself. Are they commercially available, I can't see any on mybususl site, Ceeway.

I need to use a 31.7 ID seatpost. Currently I'm using Columbus Zona double butted.

[bencooper]

You don't need specific sleeves, just a tube that'll taper over - 4130 from Aircraft Spruce comes in loads of sizes and will do the trick.

[e.Gellie]

Walking the talk. A 20 minute test and it's done. I had to do a refresher of my main-tube fillet-brazing so I chose a 1-1/8" 'seat tube' of only 0.9mm wall cro-mo. With even pre-heat and then a small enough flame to give me close puddle and feed control I got essentially no distortion and I didn't using a plug of any sort inside. I made big tacks at 6 and 12 o'clock and I use very tight, smooth mitres. My Cyclus headset-press tool happened to be a perfect fit, and proves the 'seat tube' is still nice and round. I've achieved less distortion here than I used to manage 5 years ago mucking around with plugs in head tubes with a thicker wall than this. I undercoated this to check my filing/sanding technique for undercut. I'm very pleased with the result !!! I TIG mostly, and braze the bridges and seatstays all the time but I haven't done a main-tube fillet for about 5 years. So this is essentially an update of 250-plus 'practice' joints.

This was brazed as a 'free' joint, but then I braze my frames one joint at a time, free to move as I braze. I don't tack the whole of my triangle and then braze/TIG away, because that would load the red-hot joint far more and IMO generate distortion. It takes extra time. My top-tube to seat-tube joint is the last main-triangle joint that I do and there is no tension in the main triangle at that stage.

Show us ya practice joints!

Capture2.jpg

[phutphutend]

DSC_0157.jpgDSC_0153.jpg

Right, so here we go. First test piece.

32mm x 0.9mm plain chromo. Mitred with holesaw.

First tacked at four points with no distortion after tacking. I then filleted the whole joint in one go, with no cooling in between. Result is the problematic distortion.

The first thing I have learnt is that the distortion is not cause by any kind of jig restraint.

Next I'll try a slower filleting process. Logic suggests if I fillet from the horizontal.middle towards the top and bottom in small steps the stress build up will be less.

I'll alsobdo a test piece heating to non joint side as well. And one with a big bar.

This will be after Christmas though, so bear with me...

[David Tollefson]

DSC_0157.jpg

I don't think I can get that much curve at a single location even when I'm trying to witch-wand a tube. Impressive.

Are you sure the miter is mating to the tube all the way around with no gap? I'd almost think you're getting gaps at the non-ear portion and that's closing up on you. Just thinking out loud with my limited experience (read: the voice that probably doesn't even know enough to be dangerous).

[cicli polito]

Are you cooking that poor thing? What on earth is up with that HAZ?

[phutphutend]

The white on the left hand side is a reflection. There's about 1/2mm distortion each end.

[phutphutend]

Are you cooking that poor thing? What on earth is up with that HAZ?

Sorry, what do you mean?

[edoz]

I hope this doesn't get locked before my popcorn is done.

[steve garro]

IMG_0501.JPG

My test for the day, then:

Two .6mm seat tube cutoffs, 1.125" seat tube for 27.2 post.

Result = 27.2 alignment bar passes smoothly, piece swings easily under it's own weight.

Didn't go for pretty, went for even, and .6mm is pretty extreme

It's pre and post heating.
- Garro.

[phutphutend]

Thanks.

Can you give me some more detail on the pre and post heating you performed. I assume the intention is to keep the non joint side at the same length, i.e temperature, as the joint side?

[cicli polito]

What I mean is that the color gradient inside of, as well as the size of, your Heat Affected Zone (HAZ) is to me an indicator that you have some large fundamental problems with your "immaculate" brazing technique. Notice that the arc of the HAZ on each side of the joint correlates directly to the curve of the distortion on each end of the tube you are experiencing. Control your heat better through any number of ways, and then your HAZ will shrink, and you'll experience less distortion. When fillet brazing, there really should be very little color gradient or visible HAZ at all (this is not TIG/GTAW.) Yes there will still be a HAZ of course, but it should be only slightly visible, and even.

If you're using an in-line fluxer, use additional paste flux. If you're using paste flux, use more. Work the fillet FASTER, not slower.

[phutphutend]

Is my HAZ not very similar to Garo's is size. If not in shape.

I agree it's clear to see that just one side of my joint has been heated, hence the HAZ on just one side. Whereas Garo's is equal on both sides. This is a definite contribution, if not the whole cause of my problem.

I unsure about the other comments you make. Does Garo need to control his heat better or am I missing something?

[cicli polito]

Steve is one of the best fillet brazers in the biz, and does not need to adjust anything. That tubing is also damn thin, you could hold a Zippo underneath it and get a HAZ very quickly. You personally need to work on controlling your heat better, because you haven't figured out what works best (or at all) yet for you. You are correct in noticing his HAZ is nice and even, and that should be a good hint on where to focus your heat and in which cycles.

edit* and also of utmost importance is that his HAZ doesn't follow the line/pattern of the fillet.

[EricKeller]

Are you cooking that poor thing? What on earth is up with that HAZ?

the 'cooking' comment is totally off base. His haz is too small, the distortion is coming from the unheated back side and general concentration of the heat in a very small area around the fillet. This discussion just proves my assertion that if you are going to take pictures of something, use too much flux. That's a nice looking fillet

[phutphutend]

My HAZ is 30mm from the fillet. Garo's is around 50mm. Roughly the same proportion as the difference in thickness if the tubes. Does this not suggest my level of heating is similar?

Some guidance on how to achieve the equal heating on both sides of the tube would be appreciated.