[joeavaerage]

Hi,
I have used a MIG with bronze wire, and it works OK. It's not as easy or nice as welding steel with steel wire, and the fit still needs to be good.
Molten bronze has very little bridging capabilty, unlike molten steel.

Bronze wire is worth a fortune. I worked for a company for seven years that was into welding supplies and machines. We had a couple of customers whom use bronze wire in quantity,
mainly to do electrogalved steel. A 15kg roll of bronze wire was nearly $500NZD. Even the smaller 4.5KG rolls were close to $200NZD. Second issue is that bronze wire is quite 'tender' and does
not feed well in conventional MIG torches. Both our customers used Cobra MIG torches which are motorised. They are quality US made torches and worth $4000NZD on their own.

The same company has hire equipment and I could hire a MIG and Cobra torch to do such a job, but would guess around $200NZD/day plus consumables, and the gas is not cheap!. All in all
I don't think brazing is particularly appealing as a technique, my opinion. I would prefer to weld using CO₂ shieled flux cored wire. For 9mm wall I'd use 1.6mm, or 1.8mm if I could,
for thicker sections I'd use 2.4mm. You might think gas shielded AND flux cored is like the worst of both worlds.....until you see the beautiful deep penetrating welds that end up with such a silky
smooth finish, they are a thing of beauty. Of course then you're up for stress relief.......

If besaad is planning to use gas, be it LPG/Oxy or Acet/Oxy its going to be a battle. You'll need at least one other torch just for the preheat otherwise its going to take forever to do.

Craig

[peteeng]

Hi - Obviously cost has to be figured out both ways. The frame can be majority steel welded and only braze the bits that are distortion important. You can 50% braze vs 100% runs. If TSR is available then steel all the way. All of these things have to be sorted and costed... Peter

[joeavaerage]

Hi bensaad,
may I suggest an experiment....if you are keen on the idea of brazing then try it on a smaller but realistic scale BEFORE you commit to a project that relies on it.

Get two moderate size bits of steel, say 5 kg each....and try brazing them together. If you are using gas I'll be prepared to guess that it will be hard to do. The mass of steel robs the weld
zone of heat so fast.

I have brazed cracks in cylinder heads and the secret to success was to preheat the head as hot as you could otherwise you could never get enough heat into the right zone.
We had three torches running, two for heating and one for the brazing, and they had to run flat stick all the time or.....give up! You needed big cylinders otherwise they'd freeze up
half way through the job.

Brazing small parts like ornamental cast iron or pipe fittings to a steel tube or something is easy, even fun, but when the mass of the parts go up so does the difficulty of doing it.

Craig

[peteeng]

Hi Ben - Discussing fits now. In your latest models you have the same size cross members joining to the same size verticals SHS. This means the fit is at the tube radius. This is a really big gap so usually you use the tube size down so that the fit is flat. Big gaps contribute to big distortion so make sure you design the connections to have tight fits.. Or use an RHS so you can rotate the RHS 90deg to create a flat connection if you only want to buy one size tube. Plus your cuts have to be accurate...Peter

[bensaad]

hi alls
The updated design is attached in the photo
As for welding, I'm not good at it,
I have a friend who will do this and he has done it for years,
he is using gas for welding

[peteeng]

Hi Ben - Getting refined now. Looking good. I like gas welding, is he brazing or welding? Your 120 SHS could be thinner (120x120x3mm) will be easier to weld and not change the machine performance. Peter

[bensaad]

Hi peter
He is brazing
Could I down the size of 120shs to 100mm ?

[peteeng]

Hi Ben - Yes I looked up 120x3 and it does not exist. 100x100x3 is fine. I used to live in a high house and it was held up by 75SHSx3mm. Peter

This is thinner but I expect its possible with 3mm. You can do similar with TIG and on a spot weld cycle.

https://www.youtube.com/watch?v=fWF0zCcXR5A

[peteeng]

Hi Ben - I typically use Tobin Bronze which is a zinc copper alloy. Less strength than silicon or aluminium bronze but much cheaper. Strength is not an issue with these sorts of items. If your left handed make sure you get left handed rods, much easier to use. Peter

edit - with the advent of pulse and spot welding cycles on mig and tig machines there is a trend to do a series of "spots" vs a continuous process. Some are calling this cold welding. But cold welding to me means a weld of poor penetration. Plus there are cups with legs now for spot welding that controls the stick or tip distance as you can touch the material with the cup. When I was welding and training, touching the cup to the job was a sign that you didn't have control. but now touching and rocking the cup is acceptable practice. Perhaps this cold welding is a good thing for brazing. It mimics how its done . Getting a hot spot adding some rod, retracting flame moving along close flame, hot spot add filler etc etc... This can be achieved via the spot setting of the machine. I have been meaning to borrow a TIG welder and have a play with this feature.... but a MIG with this would be easier. When I was making titanium bike frames (some 30 years ago) one of the welders dropped a gas lens cup one day and it broke off a chunk. He didn't throw it out for some reason then he started using it as a drag cup and welded through the broken side. This gave him excellent gas coverage and a shake free result. We were using 0.5mm Ti rods and magnifiers to do welds in 0.6mm tube.... with a Miller TIG syncrowave welder.