2018 December 20    Metal & Shop, Welding


Here's a blacksmith tool made from an unlikely source.

It all started when I tried to hammer some flat stock into a half-round channel.

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The Shape

Forming flat stock into a channel shape is fairly common in blacksmithing. 

Try to hammer the stock over a convex form-- such as a pipe, or the long edge of your track anvil-- and it'll probably go askew. 

The end result, if it's even usable, will be a lot of work to straighten.

Much easier to use a concave form, hammering the flat stock into it. 

Many people use one of the inner surfaces of a track anvil.  However, if you've welded steel-plate flanges along the sides, that won't be available. 

So I had an idea.

The Lawnmower Blade

An old lawnmower blade:  what kind of steel is it?  1085, 10B38, 5160... who knows?  Probably it's a medium-carbon steel, since lawnmower blades are designed for toughness rather than absolute hardness.

Carbon steels generally weld best with 7018 or 7018 AC, using a pre-heat and then a post-heat or slow cool.

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Metal Prep

So I used a Lenox Metal Max wheel to cut the lawnmower blade, removing the broken end: 

De-burr with a flap disc.

After deciding which end was going to get welded, I beveled that with the angle grinder.  (Always mind the safety precautions when using an angle grinder;  even the experienced need a reminder every now and then, because it's such a ubiquitous metal-shop tool that it's easy to get careless.)

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Preheat and Weld

After propping the pieces together as they would be welded, I preheated them.  Temperature was probably about 350 to 400 F.

Tack-welded the channel piece on with 1/8" 7018 AC at 120 amps.

Then, the full welds.  These were also 1/8" 7018 AC at 120 amps, using an AC arc welder.

Total number of welds per side was probably five or six.  I didn't keep track, but this is one project where you'll want to do more than just a single weld bead on each side. 

Then, post-heat, followed by slow cooling for a few hours. 

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Blacksmithing Test

Real hardy tools are supposed to be used with a real anvil.  Or, a real blacksmith vise that's made for continual pounding. 

This tool, however, was designed to be clamped in a machinist vise.  Or, bolt it to a wooden post or a workbench.  It could even be welded or bolted to the side of an anvil stand;  whatever works.

If the steel is 1/8" thick or less, and you've got it heated to bright orange, you should be able to form it on tools clamped in a machinist vise.  A vise would have to be extremely low-quality not to withstand this.  A heavy-duty vise should handle it indefinitely.  There's also the opposite approach, which is to use a grimy, old, cheap, imported, welded vise, which for some reason is far more durable than it ought to be.

By the time I took this photo, the metal wasn't bright orange anymore: 

So, it works.  A standard cross-peen hammer may not have been the ideal type for this, but the swage works.  Definitely a worthwhile tool. 

It no longer needs to sit out in the rain as "that broken lawnmower blade that I couldn't figure out what to do with".

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This was a look at how I made a swaging channel out of a lawnmower blade.  It's simple, and it works.

Most of us metalworkers would love to get a real swage block sooner or later;  they're highly versatile.  Swage blocks can be found from time to time on the 'bay, typically used ones, but there's always the chance someone will have new ones on there.  For now, I'll use welded-up scraps to create basic shapes such as U-channels. 

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