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First time brass brazing

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surfdabbler:
I am making some brass bolts for saw handles.  I will be getting some brass rod for the shaft, and flat stock for cutting out the large bolt heads.  My plan is to braze the brass rod onto the heads, but I have never done brazing before.  I've done plenty of electronics soldering, and a bit of welding, but never brazing.

I have borrowed a propane torch, and some silver brazing flux, and I have some 5% silver brazing rods.

It's probably a couple of days before I can get the brass, but I just thought I'd ask for hints in the meantime.  My plan is to clean the joints with wet-dry sandpaper, then set everything up on the concrete, cover the joints in flux, somehow hold the bits in place, and turn on the heat.  I'll keep trying the rod onto the joint and hopefully eventually it will just start melting and running in.

Also, the flux is quite liquid, probably the consistency of washing detergent.  Is this OK?  I shook a new pot in the shop, and it didn't slosh around.  Mine could be quite old - does it go off?

awemawson:
Most important issue is to know the melting point of your 5% silver brazing rods compared to the brass that you are using - obviously they need to be reasonably far apart to avoid disappointment.

Try and avoid doing it on concrete - it can exfoliate explosively if there is any moisture in it - a fire brick is to be preferred, or a 'Celcon' foamed cement building block.

Brush the flux on, and gently warm until the flux dries, then glazes and finally runs into the joints, then apply your silver brazing rods sparingly to the hot joint. The heat should be on the joint not the rod.

Can I suggest doing a 'test piece' first to avoid spoiling your final item.

Welcome aboard by the way. Why not tell us a bit about yourself and your projects in the Introductions section?

R.G.Y.:
The insulation building blocks are best for making a hearth,( cut with wood saw) they reflect heat as opposed to fire bricks which absorb heat. Holding small pieces against the blast of the torch. My method is press the items in to fire cement, the torch will set the cement and hold firm. Ease cracked of when finished. Kept in its original pot and moist in will keep for months. 

surfdabbler:
Had a first go today, but not much success.  The metal didn't seem to bond.  The brazing rod melted to the join, but once it cooled, it was fairly easy to crack apart.  I'm not sure about the flux.  Does it go off after years of sitting on a shelf?

I did some testing with just the flux - painted some on the surface, and heated it with the torch.  It initially dried to a white residue on the surface, but as I heated it further, the residue melted and seemed to bead on the surface.  The more I cleaned the surface, the more it beaded AWAY from the cleaned surface, which is really counter productive.

I'm using a propane torch, and it takes a couple of minutes of focused heat to get up to temperature to melt the brazing rod.  The parts are very small - I'm brazing a one-inch long 4mm rod onto a one-inch square piece of brass bar.  I'm using CIG Silver brazing flux no. 2, and Weldcorp 5% silver brazing rod.  I'm using wet-dry sandpaper to clean the surfaces (don't have a SS brush).

Any suggestions?

surfdabbler:
Some more testing this afternoon, and the results were not good.  Am I even being realistic?  Is it possible to get a strong enough brazed bond to the end of a 4mm shaft to hold a 1 inch disc on the end as a head?  A fairly light tap will just crack the 'head' off the bolt.  I am getting disheartened as to whether this is even possible with brazing, or whether I need to sand cast a bolt, and the equipment required for that is definitely out of budget.  Anyway, I'll be off to the shops later this week to get some new brazing flux and see if that goes any better.

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