Can you straighten a mower blade?

[pfrederi 21,216]

In continuing the saga of a loaner came that came home I was trying to sharpen the blades my nephew damaged.  Working with them I realized one blade has developed a  bow ...both ends bent up .  Sitting on a flat surface it rocks end to end. The other two blades only move slightly.  I put it in my 20 ton press and you could see it flatten out but when I released pressure it sprang back.  It was the most damaged of the 3.

 

Anything I can do???

[ebinmaine 80,896]

Flattening that in a press probably won't be able to fix it.

 

If you don't have to go very far I would be tempted to, over straighten, so to speak.

Go slightly past the point that you think is straight and let go.

Probably have to put one end in a vise and use a large wrench maybe even with a convincing pipe?

[ri702bill 13,181]

39 minutes ago, pfrederi said:

the blades my nephew damaged. 

Well that says it all. I'm a nice guy, but not THAT nice (ask my kids). Your nephew needs to procure a new set of blades for you. Even if they are NLA.  A little "Visual Reinforcement" of the money leaving his wallet does wonders. Seriously, blades are tempered - they bend once, then fracture & break if force is applied in the opposite direction. Not worth the damage they can cause. Reminds me of Ralph Nader's book on the Corvair - Unsafe at Any Speed...

DO check the accompanying spindle for being bent too....

[Ed Kennell 47,579]

Probably have to heat it to remove the temper. Bend it and then retemper.       Being bowed may not matter if you can get the blade tips at the same elevation.

[953 nut 69,765]

3 hours ago, ebinmaine said:

over straighten,

I have done this once with fairly good results, the blade was sprung about 1/2". I put 2" square tube pieces under each end and used the hydraulic press and went about 1/2" past straight, checked and it needed a bit more than that so I settled for 3/4" and let it in the press overnight and it was about 1/8" overbent, close enough for me.

2 hours ago, ri702bill said:

check the accompanying spindle for being bent too.

Bill, that was my thought too.  

[ri702bill 13,181]

11 hours ago, Ed Kennell said:

Probably have to heat it to remove the temper. Bend it and then retemper.       Being bowed may not matter if you can get the blade tips at the same elevation.

You would need to check and validate the hardness of the blade before and after annealing and finish tempering. Without knowing the exact metalurgy of the blade material - that is a crapshoot at best. Sorry, unless you have extensive blacksmithing experience, that is not a proven backyard "here, hold my beer" process. Those blades are best relegated to be wall hangers.