Blacksmithing with an arc welder.

[FrighteningRod]

I have a couple of slasher blades which got a bit bent and twisted thanks to hitting a eucalypt branch hiding in longish grass.

If they were mild steel I could unbend and untwist them without a problem but they are made from a VERY hard steel and I've got nowhere bashing them with a decent sized sledge hammer.

The steel is 4 mm thick and 8 cm wide.

I don't have oxy or propane (or a blacksmith's forge) and I'm out the bush with an hour's drive each way to an engineering shop. Would like to get this job done ASAP, the shop always has a week or so delay for such jobs.

I'm wondering if I could mount a blade in my trusty Dawn 125 vice and run a 2.5mm rod along the bend/twist and get the steel hot enough to work back into shape? And, although they will only be used for easy slashing once sorta straightened - no more long grass with hidden branches to slash - should I worry about annealing or quenching or just let them cool after straightening??

 

[CA_Bgrwldr]

Since you have a welder and a vice, I would weld up a jig to use in the vice. I would take some angle iron, like 8cmx8cm given the depth of the blade, and cut three 3cm sections, then cut some 1cm round stock into 3cm sections and weld it to the angle iron. Place two on one side of the vice, one on the other, place the blade between them, and use the vice to apply pressure to the blade on both sides of the bend to try to straight it out.

 

[FrighteningRod]

Since you have a welder and a vice, I would weld up a jig to use in the vice. I would take some angle iron, like 8cmx8cm given the depth of the blade, and cut three 3cm sections, then cut some 1cm round stock into 3cm sections and weld it to the angle iron. Place two on one side of the vice, one on the other, place the blade between them, and use the vice to apply pressure to the blade on both sides of the bend to try to straight it out.

Thanks CA but unlikely enough force could be applied without heating the steel, and might strip the screw threads on my ancient vice.

 

[CA_Bgrwldr]

Thanks CA but unlikely enough force could be applied without heating the steel, and might strip the screw threads on my ancient vice.

If you feel the vise isn't up to the task, I found this DYI jig online, which might be more useful. With a jig like this, you might be able to use the heat from a bead of weld on the back side of the blade to relax the bend enough to make the blade useful again.

 

[Gary Fowler]

I am not sure of the term slasher but assume from the size of the blades it is some type of light duty mower. 4mm is a lot too thin for USA bush hog type of mower so I think you have blade similar to a lawn mower. With that assumption, you might be able to put it in a small camp type fire to heat it up enough to be hammered back straight. I would not start welding on it which would cause imbalance issues.
Of course the best thing is to just buy a new blade if possible. I have bent lawnmower blades and they are almost impossible to straighten even using anvils, sledge hammer and big vises due to the hardness of the material. Heating them red hot removes the temper which is also hard to put back without a forge.

 

[CA_Bgrwldr]

I am not sure of the term slasher but assume from the size of the blades it is some type of light duty mower. 4mm is a lot too thin for USA bush hog type of mower so I think you have blade similar to a lawn mower. With that assumption, you might be able to put it in a small camp type fire to heat it up enough to be hammered back straight. I would not start welding on it which would cause imbalance issues.
Of course the best thing is to just buy a new blade if possible. I have bent lawnmower blades and they are almost impossible to straighten even using anvils, sledge hammer and big vises due to the hardness of the material. Heating them red hot removes the temper which is also hard to put back without a forge.

By "slasher" I believe he means a machete type of blade, like you see the bad guy use in slasher movies.

 

[California]

... you might be able to put it in a small camp type fire to heat it up enough to be hammered back straight.

For preheating a small cast iron weld, I used the propane burner intended for a turkey oil fryer. Plenty of heat.

Similar to this 55 k BTU unit. (A kitchen stovetop is 10~12 k BTU).

 

[MFdownunder]

A simple forge which could do this can be based on an old plough disk. Pack the bent section on a bed of charcoal and surround it with more charcoal. Get a vacuum cleaner that lets you plug the hose into the discharge side to provide a good air blast directed towards the fire. You'll have that blade red hot (or better) in no time. Quench as required.

 

[Gary Fowler]

By "slasher" I believe he means a machete type of blade, like you see the bad guy use in slasher movies.

I think, Aussie "slasher" is slang for USA bush hog. Someone correct me if I am wrong. However 4mm thickness is more like the thickness of my lawnmower blades for mowing grass and small weeds only. I wonder why the OP hasnt commented on this.

 

[GaryTN-TX]

I have a couple of slasher blades which got a bit bent and twisted thanks to hitting a eucalypt branch hiding in longish grass.

If they were mild steel I could unbend and untwist them without a problem but they are made from a VERY hard steel and I've got nowhere bashing them with a decent sized sledge hammer.

The steel is 4 mm thick and 8 cm wide.

I don't have oxy or propane (or a blacksmith's forge) and I'm out the bush with an hour's drive each way to an engineering shop. Would like to get this job done ASAP, the shop always has a week or so delay for such jobs.

I'm wondering if I could mount a blade in my trusty Dawn 125 vice and run a 2.5mm rod along the bend/twist and get the steel hot enough to work back into shape? And, although they will only be used for easy slashing once sorta straightened - no more long grass with hidden branches to slash - should I worry about annealing or quenching or just let them cool after straightening??

The risk of injury from a flying piece of metal would outweigh the cost of a new blade

 

[Gary Fowler]

The risk of injury from a flying piece of metal would outweigh the cost of a new blade

Properly heating and cooling carbon steel (mower blades, etc.) has no risk of causing breaking. The biggest change could be lack of hardness if improperly heated and cooled which would make them more susceptible to bending rather than breaking. I am amazed at the number of folks on a welding forum that thinks you shouldn't heat, bend, weld etc on a piece of steel to correct flaws.

 

[Battered Savaloy]

I think, Aussie "slasher" is slang for USA bush hog. Someone correct me if I am wrong. However 4mm thickness is more like the thickness of my lawnmower blades for mowing grass and small weeds only. I wonder why the OP hasnt commented on this.

Well, you're right, though not really "slang", just a different name for the same equipment.
We do not use the term "bush hog" here, they're sold in stores as slashers.
I'm surprised by the 4mm blade too, that's residential mower thickness.
The two blades on my slasher (Australian made) would be 10 -12mm thick.
This might be 4 to 6 small blades mounted to a large disk.

 

[Gary Fowler]

Well, you're right, though not really "slang", just a different name for the same equipment.
We do not use the term "bush hog" here, they're sold in stores as slashers.
I'm surprised by the 4mm blade too, that's residential mower thickness.
The two blades on my slasher (Australian made) would be 10 -12mm thick.
This might be 4 to 6 small blades mounted to a large disk.

After your confirmation of the name and the 4 mm thickness, I think the OP just has a regular lawnmower, either push type or maybe riding lawnmower. Either way, heating to straighten would just be a temporary fix, good for short term use till new blades can be bought. I have successfully straightened lawnmower blades with hammer and anvil. I have also did weld metal build-up on the ends where sand wears them thin at the lift wings(turned up end pieces- dont know the proper name for them). I just weld up the thinning areas then grind it as needed to balance them again.