Thursday, June 21, 2012


I haven't brazed a lugged frame for a while, but I did today.

Since I last posted brazing photos, I've replaced my torch.  I was doing a second pass to build up some filets when the old torch started to go crazy.  I replaced the valves, but it still wouldn't hold a position for either gas or 02, causing the flame to keep changing.  Random flame size and gas/02 mix make it hard to braze.  And the second pass came out very lumpy.  Naturally, I caught plenty of grief for it.

But that issue is long past.  I use a Smiths torch, which offers a life-time warranty, so I'll have to send the old one in for service one of these days, which will give me a spare.  That's one of the benefits to using high-quality American products.

Anyhow, today I was doing a double oversize frame with Dazza's Slant Six (actually they have a new name now, but its less memorable to me, in my old age). .

Sunday I installed the brake cable tunnel in the top tube, and mitered and fit up the main triangle.  Finally, I brazed the chain stays to the  BB.  I like to do this first and insure my alignment between them and a foundation of a frame.  I use brass filler here, and then use silver later when installing the seat and down tubes.

Today I started by installing H20 mounts, and a chain catcher and cable stop on the drive side chain stay.

From there, I cleaned up the lug edges, sanded the insides to a clean fresh surface, cleaned the tube ends, inside and out, and fluxed the mating surfaces on the lugs and tubes.

Then its time to put it all together in the jig, and set the pins that will hold everything together.  I don't know about anyone else, but I find this to be a messy job, with flux slipping out of the joints, while I try to hold the everything together as I fit the jig back to the frame (or is it the other way around?). 

Also, there are always one or two pins that want to come loose as I set other pins.  It's important that the pins hold well, because we move from here to the alignment table and I don't want things shifting between work stations.
First I double check the chain stays - they're centered to within less then a mm.  BTW, that's my antique Starette height gauge that I got for a song on theBay - it works great and much cheaper than anything new.

Now lest you think I'm cavalier abut the rear alignment, my experience is that heat in the frame will shift the stays - so there's no point in trying to move things around.  We'll check again later.

Next I check the alignment of the main triangle.  The down tube needed a little adjustment (about a mm), it required the remove of a pin, and its replacement in new location.  Then all looked good, so I made sure the pins were tight, one more check and its time for flux.

The Slant Six upper head and (and especially the) seat tube lugs are long.  So the filler needs to be pulled a bit farther than with some other lug sets.  But I use Stainless Light Flux, which is effective at cleaning, and holds up well to time under heat.
That's a fluxed joint with pins sticking out.  Which naturally leads to brazing.

There are a couple of spots with a little overfill, but not too bad overall.  Since these pix, I soaked the flux off the joints, trimmed off the pins, filed the pins down on the inside of the head and seat tubes, and reamed and faced the head tube.  I should have taken a picture of the faces, which have a perfect circle of fill between lug and and tube, maybe I can add those pix later. 

After than, it was time for an hour and a half riding, then dinner, and off to write you a few blog posts.  All in all a busy and productive day.

1 comment:

Trisha said...

Thanks for sharing your experiences here on your blog.