Brazing and welding sequence, how do you do it?
 

I'm sure you all do not use the same tube brazing sequence with your builds, just how do you do it and why? I am primarialy interested in lug and fillet brazing steel sequences, but how is it different with say TIG and aluminum?

From the Frame jigs and tools thread:

Cassave "I generally use Unters assembly method as well, DT+HT, ST+BB shell, braze the DT to BB shell joint then add the top tube. No locked stresses and an easy coldset before the TT goes on if required. Then add the rear end."

This is the type of info I'm hoping will be posted; I never considered cold setting before the main triangle was finished.

I've read Paterek but thats about it. And this with Mr Tanabe brazing the BB last in the main triangle sequence, http://www.youtube.com/watch?feature...&v=0AMfK1OS_mc
which I think is a great example of heating the bb.


Thanks, Brian

This is probably up there with dywall technique. Resistant to standard internet search protocall of gathering all the info, and mixing and matching. There are many ways of doing it, but it is best to find one (probably not Paterek) method, and work at it consistently. The process that is chosen will probably depend a lot on everything. So an idea here or there is not as useful as understanding one process.

Stuff like woodworking, there are often multiple steps each of which could be undertaken any of a hundred ways, this isn't because it is easy, it just doesn't accumulate in the same way. The wood doesn't really care whether it was sectioned with a bowsaw, ryobi, bandsaw, table saw. It is a discrete process. But a method designed for tig probably will not work without the same sequence tooling, etc...

The reason I say not P is because he came at it from a machinist perspective, which was overly complicated and to some extent expensive. He deserves credit for thinking out of the box though.

I use my interpretation of the Tanabe-san sequence. First I braze the fork to get a definite fork lenght value. I mitre all the tubes and add the braze-ons. Next I braze the TT-HT, then tack the TT-ST and adjust for twist if necessary. You need to properly locate the TT intersection point and phase the BB mitre. For a fillet brazed bike the shell is tacked (tinned at the front quadrant). Next I check the DT fit (it may need minor adjustement) and tack it at the HT (and the BB if doing a fillet brazed bike). For a lugged bike I hold it to the ST with small & strong magnets. Then I braze the ST-TT and DT-HT and finish with the BB. Then the chainstays and finally the seatstays.

Everyones technique and sequence will no doubt be a bit different based on experience, and what works for them. The path I follow is dictated by my frame fixture. I use the term fixture loosely- and I certainly wouldn't call it a jig (as we've come to know frame jigs). It's a homemade affair, and holds the tubes in alignment after all the mitres are cut. So the first joint to brazed is the seat tube to bb shell. I finish the fillet at this joint because the downtube will hide the front of the seat tube to bb fillet. The I tack the downtube and top tube to complete most of the triangle. I add the head tube last only because that's how my fixure dictates it's use.

I built this "fixture" to hold the tubes in alignment, and match the full size drawing. It has some drawbacks, but works well enough that I haven't been tempted to change it up. After tacking all in the "fixture" I pull it to finish brazing.

Have any pics of your fixture you're willing to post?

thanks, Brian

I do- but I'm really lazy when it comes to getting pics off the camera. LOL I'll see how I do over the weekend.

Reynolds in its Technical Advice for 531 recommends this sequence:

Scooper's post is what i remember from the late 1970s when i first started this stuff I've pretty much followed this except for when i went through my "hockey stick" phase Andy

Calstar- Hope I can make this happen- here is pic of "fixture."

http://imageshack.us/a/img692/4157/framejig.jpg

I want to make it clear- this is by no means a recommended way to do it. When I built my first frame I was looking for a way to hold the tubes so they would be somewhat in plane, and I could compare them to the drawings. I never intended to build a "jig," nor did I intend to buy one. I just needed something that would hold the tubes tight to the plan. Once the frame sizing and geometry were on paper... in my usual fashion I scrounged around the shop for stuff I had that would serve the purpose.

I wanted something that was adjustable to a degree, and was flat enough overall that I could use it to measure basic (front triangle) alignment once the tube were clamped in. It's probably not obvious from the pic but I knew going in that bottom bracket alignment, and head tube alignment weren't going to be doable in the same manner as traditional jigs. So... I cheated.

I used a base of MDF small enough so I could see the important points of the original drawing. I don't know if the base is obvious in the pic or not. Since I desired some method for adjustment, and needed a point to clamp the tube to, I used a couple (well actually three) of frames from wood working clamps (think T-slots). These were screwed to the base. I cut some angle and slotted the attaching holes so that when fitted to the (T-slots) I had some adjustment. The angle provides the surface to clamp the tube to, aqnd the toggle clamps you see hold the tubes to the angle.

There is a method for holding the BB. It's just a piece of 1/4" flat attached to the base. I needed to secure the BB (obviously) and provide for a square atachment. To center the BB (or the seat tube on the BB) I use a couple of threaded blanks screwed into the shell to adjust it's height.


As I mentioned before, the head tube joint fitting is last- but not least. I didn't have the desire or (wherewithall) to to locate the HT relative to the other tubes by the traditional "cone method." So... I reasoned that if my miters were correct (phasing. angles, etc) I could pop the head tube in last. It actually doesn't work out too bad. I tack the ST-BB-DT and TT (all the miters have been made to accept the HT) and secure it in the clamps. Then alignment checks are made to insure all tubes are centered and in plane.

Next the finshed head tube is held to the DT-HT joint by the crude clamp you see in the pic. Hopefully the mitres, offset, and angles are correct. It's easy to measure at this stage. If it's off slightly- you have the DT-TT where you want them so one can adjust them with a file easily (you ain't gotta a lotta room for error or the lengths will change.) Once lined up- tack 'em and go.

I only intended to build one frame when I devised this method for holding things. It has some limitations but actually works quite well, and the frame off will be #14. Plus... I might have only $15-20 in it, at most.


I by no means present this as a/the way to do it. I only put this out there to show you can get it done without spending big bucks- for us home hobbyist types of course. If I were doing it commercially I'd figure out a system that was a bit quicker.

^^Thanks for posting the pic and regarding the statement "... in my usual fashion I scrounged around the shop for stuff I had that would serve the purpose", I really like seeing the "home-brew" solutions people come up with, very nice.

Brian

Thanks for sharing reddog.

'Cool thread. I never thought about using magnets. I usually avoid them because they bend your arc when TIG welding. I think reddog is on the right track. One should start with a minimum of tooling but I go to old machine shops and stay far away from home depot or any franchised hardware store.

Here are a few shots of the sequence I mentionned.
1. TT-HT is brazed and ST mitre is checked
2. ST is tacked and checked for twist
3. check for DT fit (with dummy BB on the other end), then tack DT
4. braze ST then DT (it's a mixte)
5. nice stress-free fit (stuff did move when brazing so I had to coldset the ST a bit)

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