Seat tube distortion...

[phutphutend]

Firstly, I'm new to this forum. So hello, I hope we can have a fruitful experience!

I have been making brazed steel full suspension frames for a while now, at frame no.12. And I'm just starting to sell to the general public. I'll post up some more details of my work at a later date. But for now I need your help...

On some of my frames, I'm suffering from distortion of the seat tube at the joint to the top tube. The seat tube ends up with a slight bend, that makes getting the seat post in difficult.

The distortion is obviously due to the brazing setting the joint side when hot, that then causes a bend as the joint cools and the stiffer jointed side cannot expand as much pulling towards the top tube. I should probably do some tests, but I'm not sure if it occurs at the tacking or filleting stage.

I've tried to do the tacking very slowly, i.e. letting cool between each tack. This has had differing success. On early frames, I stuck a big bar in the seat tube whilst filleting, but the heat sink effect made the brazing difficult. I like to braze with a very localised heat.

I've read on here talk of seat tube sleeves, but I'd prefer to stick with externally butted seat tubes. Unless someone can convince me otherwise.

Please let me know your thoughts? I look forward to your replies and getting involved in this community...

[Andrew R Stewart]

Other more experienced builders will have more to say but warping from heat is largely dependent on wall thickness, amount of heat applied, duration of heat and evenness of heat. So using a sleeve, brazing more quickly, adding heat on the back side of the ST all would make a difference.

Some might site this example as to why a lot of practice is needed before going pro. Andy.

[e-RICHIE]

Some might site this example as to why a lot of practice is needed before going pro. Andy.

I would agree. You can't take money when questions like these still loom.

[e.Gellie]

......... I should probably do some tests, but I'm not sure if it occurs at the tacking or filleting stage.

...

Yes. I suggest you do some tests. You will benefit by getting the hang of doing quick and targeted testing. It'll be the best value lesson you can get. And you'll become the expert. I'd try a few tests just tacking and then some 'identical' except progressed further to fillets. It feels good, and sounds great to tell your customer "I've done testing and I'm all over this". Perhaps you might let us know any results of testing.

Pre-heat could well be the key; more of it, further away from the fillet.

What might not be clear is that the experienced framebuilders are doing these tests as required, and proving to their (customer's ) satisfaction that it's 'solid'. That's how they got to be experienced. Says me who perhaps did not do enough testing of some things when I was younger.

[e-RICHIE]

The distortion isn't a result of the heat; it's a result of heat control. Too much time. Too much time in one place. Brazing under load. Brazing in the fixture. Look at your processes and set-ups and determine what there is being forced, even if it's just your hand holding the torch.

[phutphutend]

Thanks for the advice on how to resolve this problem. I'll try do some test pieces and feedback the information.

The distortion definately isn't a result of too much heat. I braze using a method of low heat with a small flame for a minimum time as taught by the Bicycle Academy here in the UK. The heating is very localised, perhaps this is the problem? Too localised, rather than too much.

I also doubt it is due to the fixture, as my seat tube is held in position by a long length of 12mm bar which is pivoted at the top. As such it's very flexible in the direction of the distortion.

But yes, I'll systematically work out what the cause is and resolve it. I was hoping for a quick fix answer, but perhaps this was too much to expect. However, any more thoughts are appreciated. For example the results of anyone elses tests?

Does anyone use a rigid bar in the seat tube to keep it straight. I was thinking of this but turned down in the joint region.

Finally, although most comments have been appreciated, the ones saying I should be more accomplished more before selling were less so. I think it is my responsibility to manage my clients expectations. I see this kind of comment as just negative gloating and would prefer not to received it.

[e-RICHIE]

Thanks for the advice on how to resolve this problem. I'll try do some test pieces and feedback the information.

The distortion definately isn't a result of too much heat. I braze using a method of low heat with a small flame for a minimum time as taught by the Bicycle Academy here in the UK. The heating is very localised, perhaps this is the problem? Too localised, rather than too much.

They're showing you how to braze, that's another world from teaching you. You've never done it before. Now, after watching an instructor, you're mirroring his actions. The key is to turn up the volume, work fast, use intuitive skills, and move on to the next task. It's normal that you can't do this so early on in the assembly cycle. You're naturally scared of what a big hot flame will do. The only way to allay that fear is to line up dozens, if not hundreds, of surrogate joints and practice relentlessly.

[phutphutend]

They're showing you how to braze, that's another world from teaching you. You've never done it before. Now, after watching an instructor, you're mirroring his actions. The key is to turn up the volume, work fast, use intuitive skills, and move on to the next task. It's normal that you can't do this so early on in the assembly cycle. You're naturally scared of what a big hot flame will do. The only way to allay that fear is to line up dozens, if not hundreds, of surrogate joints and practice relentlessly.

I'm afraid not. The Bicycle Academy teaches a way of brazing different to the traditional expectiations. This uses the same princiapls and those used by Brian Curtis. The founder has put a lot of thought into the science behind brazing.

Using a small localised frames you can create a smooth consisitent fillet, with minimum heat impact on the tubing.

My brazing as a result of this is immaculate after only a handful of frames. He has also taught a number of well respected 'big names' and converted them to his approach.

[bill meyer]

Finally, although most comments have been appreciated, the ones saying I should be more accomplished more before selling were less so. I think it is my responsibility to manage my clients expectations. I see this kind of comment as just negative gloating and would prefer not to received it.

So it's ok ask respected pro's for free advice, but also specify under what terms you'd like to receive it? Reminds me of how I ask my Dad for advice...

[fortyfour]

Finally, although most comments have been appreciated, the ones saying I should be more accomplished more before selling were less so. I think it is my responsibility to manage my clients expectations. I see this kind of comment as just negative gloating and would prefer not to received it.

If I may clearly state for the record Joe, I do not believe anyone here who does this professionally is gloating nor are they being negative (Steve Garro and Richard Sachs are not exactly just anyone - these are two highly skilled professional F'builders with well established brands who have been around the block and then some). No one has ill-intent here who is a professional. Take criticism in stride. Do not take anything personal. This is all free and friendly advice.

If there is one thing that I would recommend to anyone, it's this: Practice. And plenty of it. Basics such as heat control, and it's brother distortion are mastered not in the short term, but in the long term. This takes time. Some have a natural knack for it, while others it just takes more time and dedication. There is no real number nor is there an answer in the back of a book. It takes a lot of time, patience, dedication and repetition to fully understand basics so that they become intuitive. Intuition and reacting to what the material is doing takes time and dedication to see it through to completion. You need to act and react without even thinking about it. It needs to become part of your physical DNA. And just when you think it is mastered, think again. Put your head down, be humble and understand you're not there yet. Keep practicing.

Every time I pick up the torch I feel I'm learning and improving my skills and never do I think that I can't use more practice. Never.

[Amaro Bikes]

Take any master's free comments as gifts, because it's what they're

And one should not get upset when receiving a gift. Just learn to open it

[jon_norstog]

One of the first things I figured out - there wasn't any internet on the Big Rez in those days, and no discussion groups like this anyway - was to use some kind of sleeve around the seat cluster. Another thing I learned right off was with fillet brazing you get better results if you use a heavier head tube and BB shell, and/or a smaller fillet. I would get depressed looking at my headtubes - looked like a boiled hot dawg! Then I saw a Landshark and it had the same HT distortion!

Yeah, use the sleeve!

jn

"Thursday"

[jclay]

Aside from general heat issues perhaps the order in which you complete the joint is contributory? Re the plane of the frame, which is finished last, the acute crotch angle or the obtuse? If the acute, under the TT, might that pull the ST in the direction that you're seeing? Just wondering out loud.

On a test piece, maybe break up the fillet brazing into upper and lower halfs, test fitting the seat post at the end of each half, to determine when the distortion occurs. After tacking too.

[steve garro]

Aside from general heat issues perhaps the order in which you complete the joint is contributory? Re the plane of the frame, which is finished last, the acute crotch angle or the obtuse? If the acute, under the TT, might that pull the ST in the direction that you're seeing? Just wondering out loud.

On a test piece, maybe break up the fillet brazing into upper and lower halfs, test fitting the seat post at the end of each half, to determine when the distortion occurs. After tacking too.

No.





- Garro.

[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.

[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).