Mark- Thanks for the added data. Zinc effects and "flux head" sort of overlap IIRC so I can't say I've personally experienced zinc issues although I attribute some long ago sensations of what I thought was flux related. Thankfully I am one of those people who is less sensitive to fumes in general (or less bothered at least) but still try to avoid what I can. It's real easy to get into the habit of placing one's head over the work, right in the plume raising up.

When I started out there still was Cad containing silver fillers (and IIRC there was a reluctance to move on from them as Cad free silvers were being pushed) and I was never on top of what I was using at times when in a couple of shops. I was told to not cook the joint and keep one's head out of the plume and even if the filler had Cad it wouldn't be bad for you. I only have done this work as part of a full time day job a couple of times so constant exposure was never the norm even at its worst. Andy. (who has a project sub assembly all clamped/positioned for its tacking tomorrow)

Does anyone ever use small self tapping screws to pin these together for brazing? Or are loose pins prefered because that doesn't mess with clearances for solder flow?

Pinning tubes together to hold their position is not a universal practice among all frames builders. Where I learned to build frames at Ellis Briggs in Yorkshire, we pinned frames there while the frame was being held in a fixture that was based on a cast iron flat table insuring that the frame started out in alignment. Pinning was necessary because the frames were hearth brazed together. This is a process where a giant natural gas flame (way bigger than even a rosebud flame) is augmented with air oxygen supplied with a squirrel cage. Both head tube lugs would get up to cherry red brass brazing temperature before the brass was applied. In this case the frame needed to be mechanically held together or its design and alignment would probably be lost.

When I got back to the States and started brazing with silver and an airline torch, I no longer pinned my frames. I didn't need to. Your question opens up the bigger question on how frames are made by different builders and the philosophies behind them. These are often driven by the kind of equipment we own, Tread carefully here because each builder is going to think their way is best or they would do it another better way. The goal when brazing is to do it as quickly as possible and keep the original design intact and end up with the tubes aligned. It is really easy to get into the weeds here.

When I conceived this project, I was going to try and do it without a full jig. Having learned some HVAC sheetmetal skills since, the idea of using self tapping screws hold everything together prior to brazing seemed natural. But I doubt any builder use them since nothing is needed and pins are what is traditional, like what Richie does.

I'll probably just make a full one-off jig using brackets and hose clamps.

Andy- I recently viewed a newbie's jigging photos, for the life of me can't find it now, that showed 3D printed tube holders that are much along the lines of Alex Mead's flat plate based designs Flat Plate Fixtures – Alex Meade Tools I can't say how precise 3D towers might be (but that's not what a jig really does, maintain tracking alignment, that's what your flat surface is for) but they might be rather low cost and for those who do 3D printing, not too hard to make. Andy. (who uses nails/pins mostly to maintain rotational clocking and end point locations during the prep process and adds tacks to trap all before completing the brazing in a repair stand).

I was think much cruder and side clamping. Like gas pipe threaded into flanges that are screwed to MDF as a plate. With cut lengths and adjustment at the threaded end you could control the plate-to-tube side distance very precisely, then use long hose clamps through a hole in the gas pipe to lock the bike tubing to the gas pipe ends.The three main tubes would each get two of these 'towers' along their lengths, plus something similar for the BB shell and rear "hub".

An alternative would be to epoxy the towers to a piece of junked granite countertop.

All of this would work fine to build a frame with just one geometry, though it would be easy enough to rebuild it as needed later on. But I'm thinking $50 in materials.

If I didn't have the awesome, wonderful, terrific (trying not to exaggerate Ukrainian made fixture I use and was trying to keep the costs down, I would use wood blocks. That is if I had woodworking skills like Tandem Tom. They will look similar to the aluminum blocks Mark sells at Paragon Machine Works. Of course the Paragon blocks would work well too. I would draw my frame design on MDF board and place the wood blocks on the drawn design. It would even be possible to screw the wood blocks laid on their side to the board so they wouldn't move. I would use some kind of metal plate (cookie pan turned over?) to put under the area/joint being brazed. That would catch the melting flux and keep the wood from burning. All you're doing is putting 2 small tacks on each joint to hold their position and then going to some kind of flat surface to fine tune its alignment for the next braze.

Kontact, I wouldn't pin anything unless you have a very accurate fixture or you're setting your frame up on some kind of accurate surface plate. Otherwise you're likely to be pinning the frame slightly out of alignment on your home made holder and your pins will always keep it that way.

Thank you, yes. The "original plan" called for using my granite kitchen counter as a reference surface with the drawn plan taped to it. So pins would have served like tack welds. But given how "sloppy" I'm going to have to make the DT lugs, I doubt pins alone would have preserved angles well enough.

Last year I learned some real lessons in how things can move around when I sweated a front sight with a spacer onto an antique gun barrel.



That's good to know you can get away with an all wood fixture.

Tubes moving when heat is applied is the reason a person has to have a strong strategy in order to have a frame end up in alignment. Beginners have the challenge of figuring out the best flame pattern to minimize distortion as well as trying to coordinate those flame movements. There are lots of opportunities to get it wrong. And they aren't necessary able to see what they are doing wrong and how to correct their mistakes.

A granite surface can make a great alignment reference. Here is my building philosophy to achieve good final alignment. And this is based on a typical beginner not wanting or able to buy or use expensive fixturing. i start by brazing the seat tube to the BB shell. I'll skip the explanation of how to do that. Next I'll miter and assemble the tubes to match the frame design. We would expect our home made holding system to keep the geometry within tolerance but not able to precisely hold alignment. Each lug has one spot on the 2 tubes it's holding. The frame is now taken out of the holding thing and aligned on a flat surface (like a granite kitchen counter). The 7 spots holding the tubes together allow for some movement to achieve alignment. I next put 2 more spots on the down tube lug's available centerline space (I'm only spotting the down tube lug so the rest of the frame can still have alignment movement after it is brazed). I check and adjust alignment again before brazing that lug. Of course it is common that their heating pattern will move tubes out of perfect alignment. Put the frame back on the alignment surface and adjust and put 2 spots on the top tube lug and realign again. The spots holding the frame allow for enough movement to put it right again. And braze that lug and so on.

I can think of other ways to braze a front triangle and have it end up aligned. I have found this method that i've outlined works well for my students (that often don't have prior experience) to be able to end up with a frame that is less than a millimeter out. Tube straightness is often worse than that. I'm leaving out a lot of details because my post is just to give you an idea of my building philosophy for beginners and not be a detailed description of what to do.

I'm explaining why pinning that will restrict alignment adjustment may work against a beginner whose flame movements are much more likely to distort a frame than a pro whose precise heat pattern minimizes distortion.

That makes total sense. Thanks so much for that, Doug.

Since I was just doing this yesterday, I thought I would post some pictures:
While this is specific to the BB shell, it applies to lugs as well. I made some heavy mandrels (?) that fit common socket sizes and use them to bend the sockets and then act as an internal anvil for reshaping the lug sockets:
Adjusting the chainstay socket:
by https://www.flickr.com/photos/54319503@N05/, on Flickr
That usually opens up gaps around the perimeter:
by https://www.flickr.com/photos/54319503@N05/, on Flickr

Then I use a brass punch to close them up using the solid bar inside the socket as an anvil:
by https://www.flickr.com/photos/54319503@N05/, on Flickr

That usually leaves small divots in the shoreline/socket:
by https://www.flickr.com/photos/54319503@N05/, on Flickr

So then, I re-shape the shoreline and socket to get a nice fit:
by https://www.flickr.com/photos/54319503@N05/, on Flickr

Final fit up:
by https://www.flickr.com/photos/54319503@N05/, on Flickr