Thank you Ironbark for a very detailed explanation of your suggestions and tips. One thing i'm not sure about though is what is the correct filler rod and flux that i should look for. The last time i went to check this out there's a few types and ended up not buying any.
There are I’d say three common options for brazing steel
Manganese bronze, a general purpose rod that needs about 900 degrees, good filling capability
Nickel bronze, a high strength and wear brazing material, needs more heat, great for teeth on gears or bushings.
45% Silver, good strength, needs about 650 degrees, requires close fitting components and cleanliness. Rods are more expensive
For your job I’d either pick manganese bronze or 45% silver. Manganese Bronze needs more heat and you’ll struggle with heat but 45% silver does need good surfaces that are close fitting. If you’re prepared to do the work to get a good close fit and clean up thoroughly I’d go with the silver.
The brazing fluxes are usually high or low heat or paste vs powder choices. Basically borax to prevent oxidation and aid flow.
If you go with the 45% silver a standard paste flux will work. If you are using the manganese bronze a “Tenacity” flux for higher temperatures will be needed. For pipe-style work I’d use paste flux.
With this job if you’re using an internal sleeve I’d probably trim the handle so that there is a slight gap where the sleeve fits. This way you can get the filler in both sides and once filler rod has wicked up well then fill the gap with more braze. After it’s cooled you can grind the filler back to get a smooth surface before etch priming and painting. Clean off all the flux and muck before paint or it’ll just blister and peel.
If you elect to go with 45% silver it pays to check very carefully that you are getting exactly that. The lower alloys will not do the job. Commonly you’ll see way more 34%, 15% and 5% silver rods and someone may say, “oh you can use 34% - it’s only 2/3 the price”.
The 34% is not for high strength applications in steel; it does work for certain applications with specific steels but I almost guarantee that a mower handle won’t be made from that steel type. 15% and 5% are for brazing copper pipe not joining steel.
Also, you’re going to need to get the heat into your assembly uniformly. Then once you get a bit of a glow in the material just touch off your rod on it. The right temperature is when the rod melts on contact with the heated metal and flows smoothly.
It will be possible to get your parts too hot for the Silver brazing. They need to just be slightly above melting temperature for your rod. If it’s too hot the flux will be driven out and molten rod material will run through the joint. I heat the components to what I think is right and test touch, then heat some more, test touch again until I get a nice flow.
If you can do a bit of practice on some similar material before then you’ll get a feel for it. I wouldn’t recommend trying this for the first time on something you care about.
Best of luck. It should just say “silver brazing flux” on the flux tub.
I had a look at mine today and realised, even though I don’t do a heap of this type of work, I have several different fluxes. So I can see that the choices might be daunting.
Found manganese bronze at 2.4mm and 45%silver rods at bunnings and yes you're right the silver is double the price. Will the width of 2.4mm be ok ?
To cut cost, i think i'll be going for manganese bronze but then it says it require a copper and bronze type of flux. This is the only avail flux in Bunnings https://www.bunnings.com.au/silver-brazing-flux-250g_p5910515. The label say 'Silver Brazing Flux' buti says on the description Ideal for brazing of steel, nickel, brass, copper and stainless steel. Do you think it is ok ?.
I have doubts you’ll be able to get enough heat into your handle and sleeve assembly to adequately flow the manganese bronze filler using MAP gas. You’ll need the entire portion of the assembly being brazed to be at 930°C which I’ve only ever done with Oxy-Acetylene.
The benefit of the silver is that it only requires around 650°C which is achievable with MAP, although you’ll still need to take care to ensure uniform heating.
That flux is for using when silver brazing all the listed things, I.e. it is a flux for silver rods. If you want to try brazing using bronze filler you need a flux specifically for brazing using bronze filler rods.
It should only require three rods to do the job. I think this is a fairly ambitious first brazing project; in order for it to work you’re going to need to have every factor lined up in your favour.
My advice is just find somebody who can sleve it and weld it up properly. The way you are going is you are going to spend quite a bit of money on rods and fluxes and still end up with a joint that will most likely fail because the weight you are trying to lump around is way too heavy for this weld to hold
You've got a valid point NormK. The cost of materials is not cheap plus i need to get safety gear on top of this. It might end up more expensive than buying a replacement upper frame. Will see if i can find someone who do a small job like this. I was getting excited doing this as i may have to do a similar job on the engine starter cord assembly as the holes which hold it in place is worn out.
Hi Shannon, Not knowing where you are in Aus makes it a bit difficult but I would be happy to repair it for free but that all depends on how hard and expensive it would be to post it
That's so kind of you NormK and thanks for offering. I'm based in Sydney and yes it could be expensive to post it. Will try to find a local welder first and see how it goes.
Hello all, it's been a while since my last update. Month of July was essentially out due to sickness. I've resumed working on this handle. I've been unsuccessful finding someone to weld this for me so I temporarily fixed the handle by inserting a solid steel rod which luckily fit snugly inside the frame. I then drilled a hole on both part of the handle to secure the connection of the rod and the handle. It seems to be quite stable but will wait and see how it goes next time i mow the law, Will aim to weld or get brazing done on this. I found manganese brazing rods but the only available flux is for silver. Here's photos of how it look like.
