Nessism

Talking about the fit of the lug around the tube. Got me some Daza lugs and they fit super tight. An hour of sanding and filing and now the fit is snug but not tight. Okay for 56% silver or keep filling?

fietsbob

Silver does melt flow into a smaller gap,
but maybe you will scrape all the flux off
putting the parts together ,
and that wont help the penetration, flow ..

unterhausen

if the tubes fit then you can braze it with silver. I'm no expert on bronze, but I suspect the same is true there

Nessism

I'll have one more small go at increasing clearance a smig and then call it done. Thanks for the feedback guys.

BTW, Joe Bringhelli brazed a sample joint for my edification back when I was first starting out learning how to build frames. He grabbed some random lug from his stockpile, forced it onto a tube, and then brazed it on with brass. Pretty sure the fit was as tight or tighter than what I'm dealing with. I lived in the Cleveland area at that time and it was nice to have someone like him in the area to act as a sounding board. Good times!

Doug Fattic 

Be sure and check how tight the fit is in the position it will be in the geometry of the frame and not just how 2 (or 3) loose pieces fit together. If the angle of the lugs are a bit different than the frames angles there could be tight spots where the silver won't want to flow. I use my design/set up fixture for this. I don’t assemble the whole frame in the fixture but only check the fit of the 2 tubes coming into the sockets of one lug at a time. Otherwise some other portion of the frame could be influencing the joint being checked.

You also want to check if both the tube and lug socket are round. It is common that something is oval and so only some spots are causing friction. This is more often with chain stays fitting into shells but it is not uncommon on the main triangle. Squeezing parts in a vise and tube blocks can help correct the problem. This is where a calipers is helpful to check sizes.

One of the best ways to enlarge and also make a socket hole more perfectly round is by using a good quality lug vise. It can stretch the hole just a smidgen larger. This was one of the 1st tools I had made when I returned from my apprenticeship in England years ago. It is easy to overdo it if one isn’t careful. Another way besides filing to remove a little of the socket is with the right size stone in an air grinder. A drill (with unfortunately much lower rpms) can be substituted if one doesn’t have a compressor.

One doesn’t want to randomly grind and file everywhere but only on the high spots. Sandblasting a lug makes it easy to see where the scratch marks exist. Even without that marvelous tool, is still possible with close inspection to tell where the 2 are rubbing the most.

The fit you are looking for is the ability of the tube to move freely without any play in the socket.

Andrew R Stewart 

The way I learned to fit lugs in a tube WRT silver or brass clearances is this. Silver- the lug should easily slide on the tube but tend to stay in one place unless the tube end is tapped on a bench top (tube is vertical). The lug will have no rock or big gaps. If the tube is coated with magic marker there will be pretty even scraps marks all the way around the tube. Brass. The tube slides on the tube more easily and drops down the tube under it's own weight. Very little marker scrapes will be seen. Slight lug rock, lug socket length dependent. Gaps should be easily seen but not large.

Brass, with it's much greater heat, will make bad fit work. Having said that we see far more brass done joints that crack and fail. Their numbers are far more then silver joints and silver is generally done by better craftsmen also. Andy