Braze-ons BEFORE Mitering?

[Ahmdo Molah]

I recall Mr. Don Ferris once mentioned*,
*bottom of post #92 , p.5 of Anvil Bikes' Smoked Out.
https://www.velocipedesalon.com/foru...009#post250009

"I make it a point to install any braze-ons BEFORE I miter the tubes if possible and certainly before I install the affected tube in the fixture. Braze-ons will distort the tubing and it can make your life miserable doing it after the frame is built because it can affect your alignment."

This makes a lot of sense. Removal of any stubborn flux or rust from soaking would be a lot easier too, as a more "direct" visual check would be possible, without say an endoscope(!). And any distortion in the tube would affect miters that were done prior to brazing (throwing off alignment).

But (if I'm not mistaken) it seems many builders just add braze-ons at the very end, after the frame is mostly welded(or brazed) together,

Why? Is the affect on alignment so small it is negligible?

Do any of you do braze-ons BEFORE mitering(?), and if you do, can you share any insights regarding;

1. How you straighten tubes if any are slightly affected after braze-ons
2. How you hold(secure) the tubes for mitering, if a braze-on say a cable stop is near the miter point

Pictures of your solutions would be great! Thanks~

[Andrew R Stewart]

That so many frames have their braze ons applied after the tubes are joined and that these frames work well enough for riders to not know any difference suggests, to me, that any alignment distortion is so small as to be a non issue.

1- I don't straighten tubes after braze ons are applied. I do make sure the frame is aligned to whatever my standards are.
2- The tube might be held in a different location if a braze on were to otherwise interfere with your tube clamp during mitering. How one clamps the tube might need to change. But this would be part of figuring this braze on before mitering thing out. Andy

[false_aesthetic]

I can't remember the exact build number but it was between #2 and #5 I added the braze-ons before I welded the frame together.

At some point I rotated the frame in the stand for better welding access and completely forgot about the braze ons. I ended up denting the frame. That, along with some other early mistakes, lead me to attaching any sort've "nubbin" toward the end of the build.

[Ahmdo Molah]

... At some point I rotated the frame in the stand ... and completely forgot about the braze ons.

SCREAM.jpg

Thanks for the heads up, or SCREAM in advance!

[Rich Beaudoin]

The general rule I use: if thing’s needs to go into it the tube wall, I braze them before welding the frame (bottle mounts, internal routing, etc). If the piece simply gets brazed onto the tube, I braze them after welding the frame (cable stops/guides, rack mounts, etc).
I don’t notice any affect on frame alignment, but I get much more accurate results with the placement of braze-on mounts when I can eyeball the whole frame.

[Curt Goodrich]

I like to braze on the front derailleur mount after the frame is built. But heating off the center line of the frame can effect the alignment. To counteract this, I flux the entire circumfrence of the seat tube at the mount. Immediately after brazing the mount on, I heat the fluxed seat tube 180° from the mount. A soft gentle flame heating until the flux goes glassy. This greatly reduces the heat warpage. I use the same technique on chain stay bridges. That's just how I do it. Ask 10 framebuilders about this subject and you'll get 11 opinions.

[Ahmdo Molah]

On tubes that get joined on both ends(all other than the seat tube), if the braze-ons are done after the joining, fluxing the interior would be difficult if not impossible.

In such case(no internal fluxing) is internal scaling/oxidation at all an issue even with the relatively lower temperatures for silver brazing the braze-ons?

Does anyone purge internally(with argon) while doing braze-ons if internal fluxing is not an option*?
* Due to preference for doing braze-ons after joining the tubes.

[Doug Fattic]

Jihoon, one of the advantages of experience is the knowledge of recognizing what is really important from just theory alone. I don't add braze-ons until the very end. That way I can position them exactly where I want using the entire frame as a reference. I'm fussy about alignment and use a full sized alignment table for greatest accuracy and convenience. Frames don't move when doing the small braze-ons and if they did a very little, you readjust after the brazing is finished. No biggie. The main reason I don't is because I usually build with lugs that require a lot of filing. To do the best job of filing requires constant changing of the frame position to place the portion of the lug being filed in the most convenient position. If the braze-ons were already attached, I'd have to constantly watch out that my wood blocks holding the frame in my vise were not clamping on them. This is especially a problem where the water bottle mounts go. It is where the wood blocks often want to be when filing. There is no need for this aggravation. BTW, Don Ferris tig welded his frame and as a result did not have to worry about filing lugs that required constant frame repositioning.

[Ahmdo Molah]

Much appreciate ya'lls reasons for finalizin' with the "nubbin".

'Seems they can be in the way whether using lugs, fillet brazing, or TIG welding the frame as in all methods the operator's preferred position would require frequent adjustment/rotation of the work(frame / sub assembly) at hand.

Going back to my concern regarding internal oxidation (if not applying flux internally), I've encountered some research topics indicating oxidation in low alloy steels at temperatures of around 500-600 deg.C (just below that of silver brazing temperatures). Of course, this would be dependent on the duration of the heat application, and in the case of such research papers the duration was many hours if not days, unlike the very short duration that would be required for a braze-on.

What have your experiences shown you about the degree of internal scaling or oxidation if any when doing braze-ons without applying flux on the inside of the tube?

Does anyone purge internally(with argon) while doing braze-ons?

[Curt Goodrich]

I don’t know of anyone back purging tubes for brazing on bits. I suspect you’re over thinking this and heading down a rabbit hole. All I can offer you is anecdotal evidence that the scale you describe is a nonissue. I’ve built a lot of frames and never seen that as an issue. Clean and degrease your tubes, inside and out, don’t over heat the brazing area and you’ll be fine. Welcome to the journey.

[e-RICHIE]

First - CPG is correct. Ask 10 framebuilders about this subject and you'll get 11 opinions.

However, with hope, framebuilders strive to do work that's on a higher plane than what's available from the industrial sector. In turn, it's important to consider that time and efficiency often take a back seat to what's right, what's best, for the integrity of the structure.

Except for some years at the front end when I knew less, I've always added the braze-ons to the tubes after they were mitered and all interference checks confirmed, but before the frame is assembled. In doing this, the lengths and miters allow me to locate the positions without issue. It also permits me to let the brazing affect the tube rather than the finished frame.

When a frame is brazed and complete, no matter how careful one is, the tubes are under a bit of load or stress, or both. Further to this, heating sections of various tubes to add braze-ons will want to move things one way or another, regardless of how small the movement is. Brazing the guides and bosses onto the tube when it's in a free state is a more rational way to get the task completed.

Everything matters. Or should.

I don't opine on these topics as vigilantly as I once did. But I'm still interested in passing on the best advice I can, particularly to those whose learning curve is just starting and don't have the benefit of trial and error that many professionals have.