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 80,904]

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 13,187]

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 47,585]

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 69,785]

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 13,187]

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.

[Lane Ranger 12,133]

Your old blades do have a home!  You can give them to your local blacksmith!

 

*******

 

 

Yes, blacksmiths and bladesmiths do use old lawn mower blades, though opinions vary on their quality for higUse Mower Blades

• Free and Accessible: Old mower blades are easy to salvage from discarded or broken lawn mowers.

• Tough Steel Composition: Most blades are made from medium-carbon or low-alloy spring steel (often around 1040–1045 or similar grades) designed to absorb impact without shattering when hitting rocks.

• Practice Material: Many smiths use them for beginner practice, learning how to flatten, shape, and heat-treat scrap metal. 

According to blacksmith communities like I Forge Iron, old mower blades are frequently repurposed into: [

• Basic utility knives and machetes

• Garden tools (trowels and small hoes)

• Shop tools (punches, drifts, and hot/cold cuts)

• Hardware and decor (shelf brackets, hinges, hooks, and wind chimes) 

• Soft Steel: As discussed on BladeForums, many mower blades are intentionally softer (around 45–50 RC) so they bend or deform instead of breaking. This means they may not hold a fine edge as well as high-carbon steel files or dedicated knife steels.

• Inconsistent Quality: The exact alloy varies by manufacturer, meaning some blades harden well while others will not harden at all.

[Bar Nuthin 3,347]

16 hours ago, pfrederi said:

Anything I can do???

What part number are the blades or the blade set?

I'm see some NOS sets pop up once in a while.

[OoPEZoO 613]

Wow....what was he doing?  Mowing through a stump field?  I think I would cut my losses with those unfortunately.  Even if you got them back to "straightish", I doubt they would balance well with that much damage.  I tend to collect old mower blades and use them as sacrificial anodes in my electrolysis tank.