How to Solder Aluminum.




Introduction: How to Solder Aluminum.

About: Awesome Gear I've designed myself.

Up until recently I didn't know how easy it is to solder aluminum with a propane torch. The torch I'm using has a broad flame so it's probably not as efficient in heating the specific area for welding. A torch with more of a pin point would do better. In either case if you have a propane torch and brazing rods you can weld aluminum. All this can be found at your local hardware store. The rod cost about $3.00.

Step 1: Get the Right Rod.

In the same isle where all the stuff is for arc welding you'll find aluminum brazing rod. I got mine at Home Depot. It has a working temperature of 700 to 750 degrees Fahrenheit. A propane torch burns hot enough to get the job done.

Step 2: Clean Your Joint

Any time metal is being fused together it's always best that you clean it off. Long story short, clean metal sticks to clean metal. I'm using a wire brush on both surfaces. Now you're ready for some heat.

Step 3: Brazing Aluminum.

Apply the flame to the joint until it's hot enough to melt the rod. When you sweep the tip of the rod through the joint it should melt in. If not, heat the joint more and check it again with another sweep. You want the metal to melt the rod not the flame. When everything is cooled off you'll have a strong joint. Check out the last picture where I tried to pull the joint apart in a vise. The metal got all bent up before the joint failed.



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112 Discussions

Nicely done instructable. I do want to try this to make some 10" aluminum lawnmower blades for my electric mower.

15 replies

Please don't! At its best, aluminum is prone to fatigue cracking; a brazed, soldered, or welded aluminum will fail very very quickly. This is asking for a large shard of aluminum embedded somewhere very painful.

That's a good point. I only wanted to do this because aluminum is so much lighter than steal. In theory, the aluminum blades(2) would require much less energy from the motors to turn. Thus, the blades might spin faster and/or the batteries would last longer per charge.

Lighter blades would only take less power to initially spin up. Once spinning the mass makes no difference to the power needed to keep it spinning. That is down to air resistance, bearing friction and how easily it slices through the grass.

Thanks nophead. You have given me something to consider.

let me know if you die

The only way an aluminum blade would work is by anodizing it specifically hard coat Anodizing, which drives the price up so I could not see any advantage. My experience with hard coat is extensive mostly being an Automotive Mechanical engineer where we used this process a lot, especially to prevent wear and add Lubricity to Transmission Valves.

Scott @Steamworks

steamworks1960, Your comment is most appreciated. I am somewhat familiar with anodizing from the aircraft world. However, I've never herd of hard coat anodizing. Interesting. Cost is always a limiting factor in manufacturing no doubt. If cost wasn't an issue, could small lawnmower blades be fabricated to allow battery powered mowers to perform better? Perhaps even more exotic materials like carbon fiber/kevlar, carbon boron etc could help. Or a laminated blade with all of these would perform best. I just want more performance. In every other motorized device out there, reduced mass combined with equal strength produces higher performance.

Although you "could" do that, as Jissan mentioned it is too soft for the cutting edge so you would need to use stainless fasteners to bolt on hardened steel blade edges.

Considering this extra complexity, weight of fasteners, pain cleaning grass off to swap them, AND that steel blades made specifically for the purpose already exist, it would be a silly thing to do.

ac-dc, you make a solid argument. It accrued to me to add a steal leading edge to the blades to aid in cutting. The steal blades would need to be thin and have holes to allow them to be mounted and replaced when they wear down. I still think there might be some performace gains from a lighter mower blade. Perhaps a composite of aluminum, kevlar, carbon fiber, and steal would create the ideal light weight but strong blade.

G-baby. I appreciate the need to tweek, alter and improve things. An aluminum mower blade is not an improvement for several reasons, only one of which is safety. The other two that spring to mind are efficiency and performance.

You mentioned that Al can be "more rigid". In the case of a mower blade that's actually a bad thing. A softer metal can absorb impacts (rocks, stumps,...), deform a bit, and carry on. A very hard metal may show less damage, but the internal fatigue builds with every impact. A soft blade will be dented, where a hard one will be chipped. Chipping is worse. The soft blade can be resharpened and used until there is almost nothing left. The hard blade will work until it fails. (And when it fails, Oh Boy!).

Regarding EFFICIENCY, it is as nophead said, the lighter blade will only save battery at spinup. Unlike a car going uphill, your blade is not fighting gravity, just grass. A lighter blade could conserve energy if you just start and stop your mower. If you mow with it, however, that's another story. Because then what consumes energy is not the mass of blade, but the blade of grass. :)

Which is where we come to "power", or PERFORMANCE. As has been mentioned, a lighter blade will not really affect efficiency. When it comes to performance, a light weight blade would likely be a negative. With the blade spinning free above the driveway, your motor probably approaches its no-load speed. This would be the same with a light blade, heavy blade, or no blade at all. What requires the motor to work is the initial spin-up, and then maintaining that speed when energy is lost to hitting (cutting) things. And what carries the motor's energy to the ground? The mass of the blade. While a light blade is easy to spin up, every impact will sap more of its stored energy, so the motor faces many sudden little load peaks to keep its speed. I.e. the motor will feel every blade of grass more. With the heavy blade, once it's going, it'll just go. It will only take an easy, steady push to keep speed, and the motor will be comfortably cushioned from all the work beneath. In fact, electrics often use a motor that is too weak to instantly produce all the force that might be needed, and instead rely on energy stored in a flywheel - in this case the blade. Light blade, light flywheel, less work. If you ever let your grass get too tall or thick I can assure you that, with a lighter blade, your mower would have more trouble hacking through it.

Here's something you should not try, to illustrate. Imagine a bicycle wheel, spinning on a stand. First, super-light Al wheel. No mass at all. If you stick your finger in the spokes, it'll stop so easily that you might not even learn your lesson. If you wanted to cut your fingers off with that wheel, you'd need someone who could pedal pretty hard to keep it going fast enough to do the work. On the other hand (because you still have another), look at a heavy steel wheel. Big rubber tire, maybe filled with rocks or lead. HEAVY! Once you have it spinning good and fast, you could stop pedaling and it'd still break your fingers 5 minutes from now. (Again, don't do this. Not with your lawn mower, either. :) )

Happy mowing!

noneYettookmyUN, Thank you for the expansive comment/explanation. I am sorry I haven't replied sooner. You made some very interesting and valid points. I forgot to take into account inertia. Ductility is also a property I overlooked when considering Aluminum as a lawn mower blade. My lawn mower has two 10 inch blades so I reasoned that a smaller diameter allowed for a extra margin of safety in a new material. Smaller things are much stronger than big things generally.

G-baby - NO - aluminum will crack under the stress due to the constant vibration due to grass clippings, dirt and out of balance - the results could be fatal There is a "solid" reason why blades are made out of steel.


I do think blade failure is a possibility. However, if great care is taken to balance the blades and there are no stress risers, the blade should hold up the the inertia of being spun.

Aluminum is soft and I don't think would be very good as lawn mower blades.

Yes, aluminum is softer than steal, but it is more ridged and much lighter. If the blade could be made with interchangeable steal inserts on the leading edges, there could be a benefit to having a set of blades that have much less mass to reduce the stress on the electric motors. This could create more efficiency or power.

Please forgive me for anything ridiculous I may say. I am renovating a vintage aluminum trailer and am sad to report that I had a little something done at a repair shop and they ended up shooting several brads through the skin of it! The holes are therefore small. I'm a middle aged woman and I do a lot of DIY home projects and construction but have yet to launch into welding. I wonder if it would be possible for me to use the product shown above and my soldering iron to repair these small holes and get it watertight again?

3 replies

I don't think a soldering iron would get hot enough. And if you could get the area hot enough you might burn the materials near it. I would use "JB Weld" if I were you.

It isn't the temperature alone. It's the Watts or Joules that are not high enough for large pieces. Your typical electronically controlled iron can be set for 850f and that's more than sufficient. But, for a large volume you might need 500W or more and most irons that can reach the required temperature are in the 100 to 150 Watt range. Sufficient for wire to wire or small tab to wire.

Thank you Mrballeng. I've used JB Weld with success on other things but only for joining metal things, not in places where the final finish of it would be important. Would JB Weld be able to polish up shiny like the surrounding aluminum? Or would I just be counting on it being a small enough spot so as not to be noticeable? That reminds me that I recently picked up a new (to me) JB Weld product at an auto parts store just because it looked interesting and potentially useful. It's called SteelStik (steel reinforced epoxy putty). I may do some research and see if this is an application where it would make sense. Thanks for the reminder! Also, do you know what would be the best product for cleaning the aluminum before attempting repairs? I've got old 1955 dirt.....putty tape.....and new auto grade caulk (applied by the same people who shot holes in the skin) all over this thing now. Something acidic? I don't want to ruin the shiny aluminum if I can help it.