Brazing the dropouts

I’ve never put a torch and brass to steel before these first few pictures…so be easy on me!  I learned to silver braze the various braze-ons on a bike and that is relatively easy, quick, and fun.  But not knowing how to exercise proper heat control, how much oxygen and fuel to make a perfect neutral flame…well…i’m in over my head.  I overheated all these joints before they warmed up enough to take the brass.  I’m not sure what I’m doing wrong, so if any of you readers can give a bit of advice please comment!  I know that practice and experience will only make it better over time.

This is the 3rd round on these track dropouts and some straight gauge 4130 16mm steel tubing (braze, heat up and remove dropouts, file off brass and flux, re-braze).  I slotted them just like regular chain or seat-stays and tried it out.  I was surprised at how long they took to get hot.  Even when the flux’s bubbles went away, they still weren’t accepting any brass.  The brass I first added just beaded up and didn’t melt to the steel.  I waited and put even more focused heat on the thick dropouts and very little of it was hitting the 0.035″ thickness ‘stays’.  Eventually, right before the steel turned that deadly red hue, the brass got sucked up by the steel and even dripped when I added too much brass and heat.  I practiced Paterek’s dual dabbing of the flame and brass rod to the fillet joint, but i was putting too much brass everywhere and it was really pretty funny.  But it was really fun too.

Next, I tried out a regular tubing joint of 0.035″ 4130 tubing and this was even funnier.  I know how to oxy/acetylene weld, or i at least learned to a few years ago and haven’t done it since, but this is a different ballgame since you’re not melting the steel to get a puddle to push along while adding rod.  You’re supposed to get the tubes hot enough and then bead the brass puddle along the joint making sure you get enough penetration and mass of brass along the joint so that it is a strong connection.  I overheated these tubes as well but learned the motions.

The same day, since I was in the mode of finishing this damned 1st frame…i just went ahead and tried the dropouts that were attached to my frame.  This went…OK. You can see the dropouts are pretty discolored, which i think means I cooked them pretty well (?)…but I ended up getting pretty good penetration with no gaps between the dropouts and the stays.  Of course, I didn’t realize this until I filed all the excess brass away (and there was a LOT of excess).  I guess that’s one good thing about fillet brazing. You don’t have to worry about burning through the metal like with TIG, having absolutely perfectly tight miters, and you can always file off the excess brass and still make it look like a pretty weld even if it isn’t.  There’s really no hiding that kinda thing with TIG welding.  Of course, you can’t hide bad welding technique if the brazed joint fails, and I will find out pretty soon if that’s the case with my first brazed dropouts!

The brass is obvious, but the other white-ish junk is the dried out flux.  I hear one has to soak that off in warm water, so into the bathtub it went for the night.  I of course first tried to wash it off…no way.  Then file…nope…that may eventually work but what a pain. It is kinda like glass on steel when it dries.  It comes off but I figured out whey people soak the flux off – it’s way easier.

“Done”…kinda. Can always do more it seems.

The same view with the flux off, excess brass filed away (for the most part…), and cleaned up with emory cloth for a LONG time.  Soaking the steel frame in the tub creates all types of surface rust, even overnight.   That’s the one downfall of steel, it hates water and oxygen! But it’s pretty easy just to clean it up with a few swipes of 180 grit emory cloth.

Fillet brazed joints are beautiful. Even these are somewhat aesthetic.  It can only get better.  It took me way too long to clean these slotted dropouts though…over 2 hours I’d say.  Of course, that’ll get better with time because I learned a ton about file techniques, which files work best and where, and my hand and forearm strength will increase by doing this a lot.  I actually was sore the next day. Popeye would’ve made a sweet fillet brazer.  This all would’ve been a LOT easier had I brazed the dropouts a long time ago – before tacking the chainstays to the bottom bracket! Next time.

Through this whole process, I have also realized that a lot of things get hidden by paint.  I cleaned these brazed joints up so as little brass was left on the dropout as I could, but I couldn’t get all of it – i just stopped (gave up) after awhile.  It wouldn’t matter so much if this was going to get bead-blasted and powdercoated since it would just get covered up.  There is no ‘lump’ where you see the brass, it’s nearly become one with the steel.  Even a flat file with emory cloth on it won’t get at it! So anyways,  I’m trying out a clear-coat spraypaint called Permalac that I’ll write up in my next post. It’s looking promising for these first bikes since it’ll allow some protection from rust and allow me to see if and where the frame cracks.

4 thoughts on “Brazing the dropouts

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  1. Overall, your braze job finished up looking ok. 4130 often has a coating on it that doesn’t immediately cook off, so cleaning the metal before fluxing is tantamount. Fine sandpaper (inside the tube as well) and then a short soak in citric acid and rinse will clean them up. Regulator pressures of 4-6psi work best for me, and I often adjust the oxygen pressure a bit lower to get that slightly fuel rich brushy flame.
    Patience and flame placement is key; keep it moving and spend more time on the thicker bits. The dropouts will need more time with the flame on them.
    This is an older post, so maybe you are past all this now.

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