Fillet Brazing Practice Question

[Mtblucas]

I decided I'd do a practice fillet braze with brass today. No plans on a fillet brazed frame in the works, but someday maybe. It went ok but not perfect. I have a question about it.

First off, I'm using oxy/acet. The brass I'm using is the cheap 5 pack of flux coated wire from The Home Depot. I'm practicing on steel cut out of a frame I built a little while ago that I'm using for scrap now (The frame didn't turn out good enough for my perfectionist mind). Anyway, I mitered it up and wiped it down with acetone (I didn't take the hydrochloric acid toilet cleaner to it, but it was pretty clean). I brazed it up and it looked as though the brass was melting in the joint nicely.

After it cooled, I took a file to it and tried to clean it up a bit. Not easy. I don't know how you guys get them looking so clean, but that's another post. After attempting to clean up the aesthetics a bit I did a strength test. I put almost all my weight on it and the metal finally kinked near the joint but the tubes stuck together. I'm guessing that is a good thing. I then continued to mess with it until I got the tubes apart. There were only a couple small spots where the braze had flowed inside the tube. When I was brazing I was getting the tubes pretty darn red. They were hot but since I was just practicing I wasn't too concerned about it because I just wanted to get a good flow with the brass. I don't understand why the brass didn't flow well even though the metal was so hot. How do you get it to flow if the metal is already too hot? Is it the cheap brass I was using? Not enough flux on the rod to adequately allow the metal to flow? Should I get some better quality brass (not flux coated) and a tub of flux to practice with? Although it was a strong joint, I certainly am not ready to be fillet brazing frames quite yet. Any suggestions are appreciated. Have a nice weekend everybody!

[Mtblucas]

I should add that I couldn't even get the brass to melt without getting the tubes bright red. Is this normal?

[claritycycler]

Dont use prefluxed rod, get some LWB(low fuming bronze) and paste flux from Henry James or similar suppliers

[Andrew R Stewart]

Since you are just practicing you need to go beyond your comfort zone. Get the tubes a bright orange. Practice keeping a practice joint at a color for a few minutes, without filler. Go all the way and purposely burn through a tube. Play with a rod on the surface of a tube and flow the brass with the flame. And clean the tubes with sand paper first. Andy.

[dsaul]

I'm no expert, but brass won't flow where there is no flux. You need to flux the inside of the joint and that won't happen using only fluxed rods. Get some proper paste flux and rods from Henry James or Cycle design and practice with the right stuff.

[Todd Mosley]

You can get a pound of LFB for about $15 at your local Airgas store. They will also have the flux you need.

[Andrew R Stewart]

I'm no expert, but brass won't flow where there is no flux. You need to flux the inside of the joint and that won't happen using only fluxed rods. Get some proper paste flux and rods from Henry James or Cycle design and practice with the right stuff.

This is not completely right. Brass will flow without flux. You need pretty high heat and gravity helps but don't believe that no flux equals no brass flow. Andy.

[crumpton]

yes. you need to study the temp to color notion of your steel and size that up to the melting temp of the rod you use. My guess is home center pre-fluxed "brazing rod" has a melting temp in excess of 1600f and that is a red hot tube.

I should add that I couldn't even get the brass to melt without getting the tubes bright red. Is this normal?

[Derek Raymond]

Practice stacking little piles of brass on the tube. Heat the tube, get a glob on, turn the flame and let the brass cool a second, lay one on top and repeat. It will help your flow and control a bunch. This is the first exercise Brodie taught in his f-building class.

[EricKeller]

I think most of us pre-heat the brass to dull red when bringing the tube up to temperature. I'm teaching my daughter how to braze, and I can tell that keeping that in balance is tricky for her. I always thought the excercise of trying to build brass towers was stupid until I did it with a beginner. She definitely learned a lot by doing it.

[Mtblucas]

Thanks for all the suggestions everyone! I will get some better brass and mess around with it some more using your tips. Hopefully I figure it out because I'm getting tired of making lugged road bikes :-) I need to build up a fillet brazed mtb frame to really make me happy!

[Will Neide]

Thanks for all the suggestions everyone! I will get some better brass and mess around with it some more using your tips. Hopefully I figure it out because I'm getting tired of making lugged road bikes :-) I need to build up a fillet brazed mtb frame to really make me happy!

Once you learn to fillet braze you can make your own lugs for a lugged mtb.

[G-reg]

Those prefluxed rods are fine for practice. But post brazing, the remaining flux is some physics bending concentrated evil. It doesn't easily soak off, is strong as diamonds, and eager to give you the opportunity to foul up some files. And that's IF you don't overheat it.

Once you get the right flux, keep it sterile. Any crap you get in there WILL cause issues even if you don't suck at brazing. I'm following my own advice soon and ordering the powder style, and mixing it up as required. The tubs of premixed have gotten a bit nasty.

[ToddFarr]

Kind of a tangent, but...I store my flux in these cute little jars....


My New Flux Containers by FARR Frameworks, on Flickr

Everytime I mix it with a clean spoon, and use cheap throw away brushes. If I double dip, I away scoop out some with the clean spoon and grab some with the brush off there rather than sticking it in the jar. Haven't had any issues, all my fluxes stay clean and don't dry up as fast as they used to in the original screw top containers. I think I picked them up at storables?

[Mark Kelly]

Known as French canning jars or "le Parfait" jars after the French (original?) manufacturer.

I have also seen them sold as "Niveau de Remplissage Jars" because the seller doesn't know that that's written on the side because it's French for "fill level".

[suhacycles]

Kind of a tangent, but...I store my flux in these cute little jars....

Hmm... I guess I can make use of that Bed, Bath and Beyond coupon...

[suhacycles]

BTW, what are folks' opinions on fillet sizes? Do you usually make them as big as reasonably possible or can one get away with making small ones that are closer to TIG bead sizes? How about heat control when using Fillet Pro versus brass?

[Will Neide]

BTW, what are folks' opinions on fillet sizes? Do you usually make them as big as reasonably possible or can one get away with making small ones that are closer to TIG bead sizes? How about heat control when using Fillet Pro versus brass?

Much less heat with Fillet Pro. Watch the flux to know when you are at the right temp, and I work a tiny flame. Keep your work side up because gravity is not your friend.

I used about 4 troy oz on my last fillet brazed frame with Fillet Pro.

[Mtblucas]

Once you learn to fillet braze you can make your own lugs for a lugged mtb.

LOL, I actually do want to do this eventually. It would be a cool project, and you'd have a very unique looking mountain bike.

[steve garro]

I used about 4 troy oz on my last fillet brazed frame with Fillet Pro.

Why?
Was it stainless?
- Garro.