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How to hold tubes together for fillet brazing without a jig

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How to hold tubes together for fillet brazing without a jig

Old 02-01-19, 01:33 PM
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How to hold tubes together for fillet brazing without a jig

If I fillet braze the head tube to the top and downtubes, what setup would work to ensure the tubes are butted tight against one another?

So I would first braze the OS down tube to the lugged BB shell and then work on connecting the OS down tube to the 44mm head tube. I wouldnt think laying the tubes on tube blocks would allow for enough pressure to push the tubes together for a tight fit. Is that totally unfounded and not an issue?


My limited experience is with lugs so I am trying to envision the setup I would need to garage build with a mix of fillet and lugs.
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Old 02-01-19, 02:04 PM
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One classic method of insuring the a lugged/socketed joint stays put is to use a pin. I will use 6d finishing nails with a slight taper ground on the end. The drill bit is a 3/32". Fit up the joint and at the proper alignment (angle, placement and steering/in plane) then drill through the lug and tube (locate the hole where later you can easily access it with a file for finishing). I actually pre drill the lug so only the tube is pierced when set up. Now place the pin/nail in the hole and lightly tap the end to set it. Some builders use a few pins per joint to better keep all in alignment during the handling when brazing.

I still will/would do a tacking braze to further hold all in place. Then I do an alignment check and bend to correctness before continuing the brazing.

Different builders have different joint sequences they do the frame in. I will do the ST/BB first as a separate step. I find locking that alignment makes future steps less complex. Some will do the entire main frame first as a single session of brazing. Others will do what's called the "hockey stick" process. brazing the main frame in two halves (like the BB, ST, TT as one and the DT and HT as the other) then join the two halves as a different step.

What you do is your choice and somewhat dependent on the tooling you have, how you control the angles/lengths, what your ability to keep track of how many elements at one time is.

Fillet joints are a bit more involved in keeping the tubes at the correct relationships, having no jackets/lugs holding ends togethers. But much the same set of issues to deal with otherwise. I do more fillet these days and use small tacks (of braze on the frame centerline) to hold tubes in place, much like the pins do. How you hold the tubes in place is some of the challenge. One way is with V blocks on a, hopefully, flat bench top with the joint hanging over the edge for torch access during the tacking. Andy
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Old 02-01-19, 02:10 PM
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Isn't there a long time builder in town there? When I stopped in Beaverdale Bikes (IIRC) last Spring I was told of the builder who lived somewhat near by. I forget his name right now (and will dope slap my head when I remember) but I remember he was slowing down his frame work. Reason I mention this is that a few sessions with someone experienced can do a lot in getting past the newbie starting questions quickly. Soon after the questions become far more focused and situational. Andy
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Old 02-01-19, 02:21 PM
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Originally Posted by Andrew R Stewart View Post
Isn't there a long time builder in town there? When I stopped in Beaverdale Bikes (IIRC) last Spring I was told of the builder who lived somewhat near by. I forget his name right now (and will dope slap my head when I remember) but I remember he was slowing down his frame work. Reason I mention this is that a few sessions with someone experienced can do a lot in getting past the newbie starting questions quickly. Soon after the questions become far more focused and situational. Andy
Ha, yes there is. Its who taught the class I took last winter when I built my lugged road frame. Jeff Bock.
I actually saw him last weekend at bike expo and we talked a short bit(he was super busy with people admiring his bikes that were surrounded by a sea of carbon and electronic shifting, it was funny).

I plan to hit him up if I get stuck on anything during the build. I find this forum(and others like velocipede) fascinating due to the abundance of collective knowledge. Its very interesting to hear different approaches because one thing I have certainly learned is there is more than 1 way to skin the framebulding cat.
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Old 02-01-19, 02:59 PM
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Braze the bottom bracket with downtube and seat tube in it put the top tube/seat tube lug on the seat tube put the top tube in the seat tube lug set the head tube where you want it against the DT and ST and use a piece of steel wire between the head tube and seat tube with a turn buckle in the middle. Tighten the turn buckle and the wire should hold the head tube in place. May need to put a spacer on the back of the seat tube to insure no kinks when tight and a couple of tube blocks to make sure the wire doesn't slip down the head tube or seat tube.

Best I can do haven't actually tried it but it sounds good
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Old 02-01-19, 03:30 PM
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I always brazed the head tube to the downtube first, as is traditional. Some people call it the "hockey stick."

I used a fixture to attach the bb shell to the seat tube and then put together the front triangle. The head tube and seat tube are usable as references then.

If you tack it, you can ensure that you have gotten the miters seated.
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Old 02-01-19, 05:53 PM
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Originally Posted by unterhausen View Post
If you tack it, you can ensure that you have gotten the miters seated.
good point- easy to heat up and remove if needed with checking after a couple tacks but before doing 2 more tacks.

there will be a good bit of practice too before. Hopefully the practice can focus on laying the fillet more than focusing on how to keep the down tube flush with the head tube.
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