Sharpening large mower blades

[daddo]

Here's what I do. You can take it with a grain of salt and do it your way- whatever works for you is good for me.

I sharpen my blades 3- 5 times a year on the lawn tractor and the push mower- I hit a lot of objects sometimes that nick the blades to the point I have to redo the cutting surfaces- a few nicks is no big deal to me, but a lot of deep nicks reduces the cutting surface by half to 75% if you only have a few bits of sharp surface left- nicks don't sharpen well if at all.
 The blade angle is important only if you get it way off like 20 degrees or 50 degrees. It is a good idea to keep the originally designed angle as close as you can. We know this using planes, though mower blades not that critical of course. The blades I have came as 35 degrees and 45 degrees. The average is 30-40 degrees.

I clean loose debris from the blade first. There will be some very small debris that has attached itself to the point sandblasting is the only way I can get it off it seems- I don't do that. That small amount isn't going to suddenly break off. Scrape it and clean it with a buffing wheel if you wish.

If I have a lot of nicks or a few deep nicks, I start the blade from scratch and sand/grind the cutting end flat. This will require a lot of material to be removed in order to keep the original angle and sharpen it once again.

 This belt grinder with a 36 grit will remove material many times quicker than a wheel grinder.





  Then I sand it down at the proper angle until we are sharp.
  When sparks are flying over the edge, it is sharp enough.






 Then I use a file and remove the lap left by grinding/sanding on the face and then use the file
flat on the back side to get rid of any ridge. You want it flat- not beveled here.





 I check the angle. Within 5 degrees is fine for me.




 Then I check the balance using the cup or the bearing thing-a-mu-jig. Removing material from an end
to get it balanced.







 I place a light coating of grease on mating surfaces including the bolt once a year.
And- NO, this will not make the bolt come loose. Properly tighten the bolt. I've been doing it this way for at least 35 years
on both the lawn tractor and the push mower and haven't even come close to having a blade come loose, and I have never
had problems removing a rusty frozen one either.
  You could also use "anti-seize" compound if you so desire.

 But if this scares you, by all means leave it dry.




   If the sound you get when cutting the grass is a sizzling noise- your blades are sharp. If the engine just bogs way down- they are dull.


 I sharpen my mulching blades just fine. You must sharpen the inside part of the blades cutting surface- a file works good there for me.

  Dull blades shred the grass when it cuts and the tops will turn brown and ugly.

  Dull blades makes the engine work harder and burn more fuel.

 I sharpened one blade so much many years ago, it was too skinny to support even a small blow from an object and it bent and could have thrown shrapnel- not a good idea!! In fact, it was stupid for me to do that just to save 20 bucks.

[Stwood_]

Excellent write up daddo.