How and when to sharpen Rotary BH blades

[sandman2234]

We also do this on our lawnmower, just have to balance them. Went from one set of blades a year, to three or four years on a set,still have to sharpen them after about three or four acres. scrapironford

Just wondering what it would cost to send them to a heat treater. No balance problems and a deeper hardness "might" be attained, depending on what steel was used in the manufacture of the blade. We tried adding Stellite welds to a blade once and it just wore around the weld. Sand is abrasive and hard on blades.
David from jax

 

[J_J]

You should only sharpen the blades if you think they ares not cutting to your satisfaction. If you want them rounded off, then never sharpen them. Just don't tell me they are cutting great. Some of you have never used a sling blade. If so, you want a sharp one as a dull one will work your buttocks that much harder, and do it on a hill side, at 95 degrees. Just tell me how easy that is. Boss man, boss man, can I have some of that water, please.

 

[scrapironford]

Sandman 2234 you have a good point on heat treating. I would expect ht blades would be expensive, was a company in Jax that heat treated a few years ago, don't if they are still in business. My biggest concern with heat treating would be making the blades to hard and brittle, as they would /could shatter on impact with a rock, fencepost ect. Someone on TBN has this answer or the ability to figure this out. Please let us share in your knowledge. scrapironford

 

[have_blue]

Sandman 2234 you have a good point on heat treating. I would expect ht blades would be expensive, was a company in Jax that heat treated a few years ago, don't if they are still in business. My biggest concern with heat treating would be making the blades to hard and brittle, as they would /could shatter on impact with a rock, fencepost ect. Someone on TBN has this answer or the ability to figure this out. Please let us share in your knowledge. scrapironford

I used to work with a manufacturer of large heat treated tools, and was involved in engineering and quality. I've spent hundreds to thousands of hours in metallurgical testing labs studying the effects of heat treatment on cutting tools.

If bush hog blades could be heat treated to 45-50 Rockwell "C", they would not catastrophically chip or fly apart, yet stay sharp far longer between sharpenings. The blades on my bush hog seem to be almost dead soft, which is ridiculous. Lawyers have spoiled things for us, mostly for a red herring.

You can't simply take any bush hog blades and heat treat them. They have to be made from a material that is heat treatable. If the metal isn't suitable for simple hardening and quenching, they can be carburized, or "case hardened".

Case hardening is the ideal condition for large cutting blades. That way, your cutting edge can be very hard and self sharpening, yet the core can be soft to resist cracking. Case hardening is expensive, because the part must stay in a high carbon atmosphere for 2-3 days at 1700-1900F.

Ideally, the bottom of a mower blade should be case hardened to around .060", and the top masked off to keep it 10-15 points softer. That way, the top of the blade would erode much faster than the bottom, leaving a sharp cutting edge. The sharp edge would chip slightly if it struck a rock, but would pose no hazard (the rock fragments would be 1000x larger, and pose far more danger). Tiny chips of metal simply will not penetrate skirts and guards.

Now,,, for my purpose, which is mowing 8 acres of weeds and grass with no rocks or bricks, a carburized blade would be awesome. If you mow junk, or mow professionally, heat treating probably wouldn't help as much. But neither would sharpening.

 

[scrapironford]

have blue : I thank you for your information. I learned something so it has been a good day for me. A guess as to how much more, $10-100 would these carburized blades cost per blade. scrapironford

 

[have_blue]

have blue : I thank you for your information. I learned something so it has been a good day for me. A guess as to how much more, $10-100 would these carburized blades cost per blade. scrapironford

You're welcome.

If you have a friend that does heat treating, sometimes they can give extra parts a free ride with a batch.

If your blades already have a little carbon in the metal, just heating them to austenitic temperature (usually bright red heat) and quenching in oil will do the trick. Hardness would have to be checked to ensure they aren't over ~50 on the C scale. 50 RC blades will hold an edge many times longer than typical blades.

 

[JIGBUILDER]

My neighbor has a older 25-28 hp ?? Kubota 4wd with a 4' mower. He has 60 acres and is continually mowing. Lots of rpm and slow ground speeds and not cutting clean. Ragged looking job.

My 40 acres back fence butts his 60 acre back fence and as all good neighbors do we meet along the fence 3-4 times a year and sit and talk. LOL he's a full blood Creek indain so I do most of the talking. He noted how clean my new 6' Rhino mower cut my pasture. I had him raise his deck for a look at his blades. Pretty bad.

We have a common gate in that fence so I had him bring his tractor to the house and a visit my little Dotco air angle grinder. It took me about 2-3 minuets per blade to get a straight 1/16" cutting edge back. Now he mows at a lower rpm and a taller gear which is a whole lot easier on the tractor and does a clean job.

This is tall grass country with big and little blue stem/Indian bunch grass/Midland Bermuda/Fescue/lots of weeds/dried Red clover which is tough and stringy/some brush and lots of sandstone rocks.

 

[Peej]

Recently saw the owner of a local implement building shop cutting out a section of an old B/H blade and was going to add in a section of Hardened? carbon steel. He cut out about a 8" section not all the way across and had a replacement section to weld back in. Said it would last considerably longer than a regular blade. Any thoughts?

 

[have_blue]

Recently saw the owner of a local implement building shop cutting out a section of an old B/H blade and was going to add in a section of Hardened? carbon steel. He cut out about a 8" section not all the way across and had a replacement section to weld back in. Said it would last considerably longer than a regular blade. Any thoughts?

He is right. It'll work fine. That would be fairly cheaper to manufacture, but still more expensive than soft steel. Manufacturers get flak from lawyers, so they cop out.

To be fair, manufacturers don't know the conditions in which their cutters will be used. Since some are used irresponsibly (mowing junk), they have to use soft blades even for responsible owners that will never mow anything harder than grass. The manufacturers use that as an excuse to use cheap, soft alloys, which are cheap and easy to manufacture. They could safely use an alloy that wears 10X longer, yet is not so hard that it would break catastrophically. (45-50 Rockwell C hardness).

 

[J_J]

I think you guys should understand that the steel the blades are made of, is good as it should be. It is soft enough so it will not fracture easily. They can be sharpened by those that want to. And those that don't care whether it is sharp or not, would just as soon use anything that is in balance. The other thing is, that they are cheap enough to replace ever couple of years, but then again some of the guys have never sharpened or replaced the blades since whenever. Next, someone will want titanium blades, or self sharping blades, or self balancing blades. I don't think anyone has improved on the bush hog blades since the first ones were made, and probably for a good reason, they seem to work for the majority of the owners. I can't disagree with some that have had success stories with the modification of the bush hog blades .