I was having a discussion with several guys about how to sharpen mower blades. I sharpen mine with the blade clamped in a vise and sharpen using a file. Done this for years because I was told by an oldtimer that if you sharpen using a grinding wheel that it takes the temper out of the blade. Is there any truth to this?
Proper sharpening of mower blades?
- Thread starter Rob Taggs
- Start date
- Status
Unless you're bluing the blade when you're grinding on it, I wouldn't worry about it too much.
I grind mine all the time. And what harm would 'taking the temper' cause - did he say? Seems the new mulching blades have been stamped in such a radical aerodynamic bend that they are disposable anyway when subjected to abuse (like tree roots on my property).
I sharpen mine by hand as well. If you do it annually and avoid mowing over rocks it doesn't take very long. I don't think most blades are tempered steel anyways but heating the cutting edge with a grinder certainly won't help.
rg144, you sound like my Stepfather. He has a few acres he mows with the rider I gave him. I sharpen his blades on a grinder, and it is not pretty. I believe he thinks it is a brush hog.
A file would just take too long to remove the imperfections after he mows. I use a Dremel for the wavy part of those mulching blades. I have not observed damage to blades due to grinding.
I've got one of those electric hand-held belt sanders that has a 1/2" wide belt (sort of like a Dyna-Brade if you know what they are). I've been using this for many years. It follows the curves on those recirculating mulching mower blades well. It doesn't heat the blade much and is easy to control the sharpening. I usually run it lightly over one cutting edge, say 50 times, then do the other cutting edge, repeat until sharp.
Is taking the temper off the blade REALLY that bad?
We have very sandy soil and I need to sharpen my blades (Honda push mower and Honda tractor) every 20-30 hours.
Often they are beyond what even a good, flat file can handle.
--- Bror Jace
We have very sandy soil and I need to sharpen my blades (Honda push mower and Honda tractor) every 20-30 hours.
Often they are beyond what even a good, flat file can handle.
--- Bror Jace
We have so much sand in our area, that it literally grinds up the blade. I have to buy about 2 blades every year.
I read somewhere that you should leave a 1/64th flat edge on the front of the blade, i.e. not perfectly sharp. How to to do this? Beats me!
I never imagined it was such a science (from "Grounds Maintenance" web site ):
"The primary goal is to consistently maintain the correct angle on the blade. Around 40 degrees is typical ... check with the blade manufacturer to obtain the exact figure. A narrower angle, such as that of a pocketknife, will cut well initially, but will dull quickly and nick easily.
Blades come from the manufacturer with a milled edge. Milled edges are the best, but machines that provide a milled edge are expensive. A sharpener with a grinding wheel is not preferred, because it will give you a hollow grind.
As you sharpen, move the blade back and forth across the grinder, maintaining the proper angle until you get the edge you need. Forcing the blade to grind faster heats the blade and will cause the metal to lose its temper (hardness of the blade). Some mechanics will keep a bucket of water handy and will dip the blade in it to cool. If the blade turns a straw color while grinding, it's too hot and the temper is likely gone."
"The primary goal is to consistently maintain the correct angle on the blade. Around 40 degrees is typical ... check with the blade manufacturer to obtain the exact figure. A narrower angle, such as that of a pocketknife, will cut well initially, but will dull quickly and nick easily.
Blades come from the manufacturer with a milled edge. Milled edges are the best, but machines that provide a milled edge are expensive. A sharpener with a grinding wheel is not preferred, because it will give you a hollow grind.
As you sharpen, move the blade back and forth across the grinder, maintaining the proper angle until you get the edge you need. Forcing the blade to grind faster heats the blade and will cause the metal to lose its temper (hardness of the blade). Some mechanics will keep a bucket of water handy and will dip the blade in it to cool. If the blade turns a straw color while grinding, it's too hot and the temper is likely gone."
This is an interesting thread. I have two mowers, a Honda Masters and a Sears Craftsman. We live where the soil is pure sand. In fact, it's called the Sandhills of NC (south central NC, near Rockingham and Fayetteville). After one season, the Sears blade was pure junk. I understand they're cheap blades to begin with. I couldn't easily find a good quality aftermarket blade either (like a Gator) locally, so I bought a "Heavy Duty" Craftsman blade from Sears. It's a little bit larger, with big wings on the end, for mulching. It cuts great so far. I'll have to watch the dullness though.
The Honda blade is still original, and cuts well. I just sharpened it a few mowings ago. I don't have a grinder, but I use my Dremel tool to sharpen the blades. Works pretty well I'd say so far. My main goal was just to "grind" it down so the face of the blade was shiny (meaning fresh metal) and the edge was relatively sharp.
Thanks for that link from the Grounds Maintenance website.
The Honda blade is still original, and cuts well. I just sharpened it a few mowings ago. I don't have a grinder, but I use my Dremel tool to sharpen the blades. Works pretty well I'd say so far. My main goal was just to "grind" it down so the face of the blade was shiny (meaning fresh metal) and the edge was relatively sharp.
Thanks for that link from the Grounds Maintenance website.
MolaKule
Staff member
Glad to hear I am not the only one to severly bend a mulching blade on a stump hidden by grass, etc.
Filing and or grinding wheel with grinding wheel at less than 1,500 rpm.
I think the important thing is that you balance the blade before reinstalling.
Using a file if circumstances permit is a safe bet, not to alter the metallurgy. You would actually have to know the characteristics of the original blade.
A lot of the cheap blades now are probably not well tempered and properly annealed anyway to begin with.
The problem is, applying high heat and quenching makes for hardening, but also brittleness. So some annealing may be in order for durability. Not a great way for the average person to do this at home with predictable results.
Probably if you don't grind agressively and keep cooling it, you probably won't take any temper out.
A lot of the cheap blades now are probably not well tempered and properly annealed anyway to begin with.
The problem is, applying high heat and quenching makes for hardening, but also brittleness. So some annealing may be in order for durability. Not a great way for the average person to do this at home with predictable results.
Probably if you don't grind agressively and keep cooling it, you probably won't take any temper out.
Originally Posted By: kenw
"Some mechanics will keep a bucket of water handy and will dip the blade in it to cool."
Frequent dipping of tools in water as they are being ground is done to keep them from getting hot enough to screw up the temper.
"Some mechanics will keep a bucket of water handy and will dip the blade in it to cool."
Frequent dipping of tools in water as they are being ground is done to keep them from getting hot enough to screw up the temper.
Here's where my almost 30 years in the heat treating business can help explain this topic.
Higher hardness in a metal normally comes with more "brittleness" Can you imagine how many foot injuries there would be if blades were hardened like knives and broke instead of bent when they hit something? They don''t need to be too hard, after all, they're meant to cut grass. So using a grinding wheel is fine, even if you see a little blue color. A local mower blade manufacturer austempers their blades. This results in a somewhat hard, but not brittle blade. Also from what I've seen some blades aren't hardened to begin with.
Higher hardness in a metal normally comes with more "brittleness" Can you imagine how many foot injuries there would be if blades were hardened like knives and broke instead of bent when they hit something? They don''t need to be too hard, after all, they're meant to cut grass. So using a grinding wheel is fine, even if you see a little blue color. A local mower blade manufacturer austempers their blades. This results in a somewhat hard, but not brittle blade. Also from what I've seen some blades aren't hardened to begin with.
Used to take the time to pull it off the mower and balance it after sharpening. Then noticed that the darn hole in the blades were almost always .080" + - bigger than the crank snout! Chances of getting it centered and having it stay that way was slim to none. So much for the balance. Now I just tip the mower on its side and do a light job with the die grinder and call it good. Too chunked up i just replace it. Fwiw I used to sharpen the very ends of the blade, not sure if it helped but seemed like it might?
Cutlery is a hobby, and I donate knife sharpening coupons for school and church fund raisers. I used a file for years on mower blades but now use a 2 in Sears belt sander for most things. I'll even use it on larger knives for the rough grind, but always finish off with stones, sticks, strops, etc.
In cutlery 'grinding' almost always done with a belt sander, as the typical rough, hard grinding wheels on bench grinders will get the material too hot, blue it, and lose the temper. It's also a possible problem with a belt sander, so you monitor your work and cool as needed. Hard grinding wheels are durable, but as a consequence they typically don't grind well as fresh abrasive isn't made available when working. Selecting a softer wheel of the correct grit makes a big difference, but it's easier to use a belt sander and that's why it's used almost exclusively in cutlery.
Sharp mower blades work a LOT better than dull ones, for cleaner cutting as well as plowing thru heavy stuff, so it's worth keeping the blade sharp. Since grass usually has lots of dirt in it blades dull quickly, mowing rocks doesn't help either, so check it often, sharpen as needed, and don't fret too much about angles and such. Just roughly follow the original angles, which will be large to minimize chipping. Mower blades aren't that expensive so having a spare that you keep sharpened makes for a quick change, and you can then ponder the technical challenges of sharpening the blade at your own leisure :^)
In cutlery 'grinding' almost always done with a belt sander, as the typical rough, hard grinding wheels on bench grinders will get the material too hot, blue it, and lose the temper. It's also a possible problem with a belt sander, so you monitor your work and cool as needed. Hard grinding wheels are durable, but as a consequence they typically don't grind well as fresh abrasive isn't made available when working. Selecting a softer wheel of the correct grit makes a big difference, but it's easier to use a belt sander and that's why it's used almost exclusively in cutlery.
Sharp mower blades work a LOT better than dull ones, for cleaner cutting as well as plowing thru heavy stuff, so it's worth keeping the blade sharp. Since grass usually has lots of dirt in it blades dull quickly, mowing rocks doesn't help either, so check it often, sharpen as needed, and don't fret too much about angles and such. Just roughly follow the original angles, which will be large to minimize chipping. Mower blades aren't that expensive so having a spare that you keep sharpened makes for a quick change, and you can then ponder the technical challenges of sharpening the blade at your own leisure :^)
Yeah, I never pulled a blade. Just tip it up and hit the blade with a b-astard (*note) file and I am done (little hard to clear the file, but it can be done on short strokes with the tip several inches of the file). If you work about as much on either end it should remain close to balance. I suppose it might be good every so often to check the balance though.
* NOTE: Seriously, this is the name of the file, but this software won't let me type it direct
- Status
