Sharpening Bush Hog

[Bird]

John, I don't have a balance scale or I'd probably do that, too./w3tcompact/icons/wink.gif

<font color=blue>they recommend replacement versus “re-sharpening”… due to the “tempered” and “hard-surface process” technology in use</font color=blue>

Makes sense and sounds logical to me. My previously owned Bush Hog manual had instructions for sharpening (and leaving a flat front edge), but in my currently owned Howse manual, I haven't found any mention of sharpening; just replacement; maybe you've stated the reason. Actually I have sharpened the Howse blades (only once in two years) and just tried to go very slow a little at a time to generate as little heat as possible (and I'm certainly not saying that was the best thing to do; only that it's what I did do).

My brother had to retire from the Tool Truck business because of a physical disability, but shortly after he retired, the guy who took over that route asked my brother to run it for a week for him because he had a son in the hospital in serious condition, and my brother did. So this time when he asked my brother to do it again, my brother said he just couldn't handle it alone, so we did it together. My brother knows a lot of the tools much better than I, and he knows the town, the customers, and the company's computer system better, so I was mostly just the driver./w3tcompact/icons/laugh.gif Lots of climbing in and out of that big truck, but I really liked that Freightliner with a 310 or 315hp Cat engine and Allison transmission.

 

[rbargeron]

<font color=blue>I understand from a lawn care friend that the outer end is where the action is. </font color=blue>

I'm pretty sure that on a rotary cutter, the main action is along roughly the first 2-1/2" of the blade. Here's how it figures: Let's say an average mowing speed is 3.5mph - or about 62" per second. Most rotary gearboxes are around 50% step-up over pto rpm - so the blades turn approx 790 rpm or 13.1 rev/sec. The amount covered by each blade is 62"/sec divided by 26.2 blade sweeps per second. So each blade cuts about 2.4" of new material each time around. Of course this is the max and it tapers down at the ends of the arc.

Whether the edge is rounded or not is more about material temper and resistance to chipping - not about how it cuts. Finish mowers and walk-behinds run much faster and cover much less ground per revolution - so it may be a factor there.

Dick Bargeron ---- cheerful refund if info is bogus /w3tcompact/icons/smile.gif

 

[pennwalk]

I decided to take John Millers advice. Picked up a set of King Kutter blades for my old KK 48" hog were $13 each from TCS. King Kutter recomends replacing the bolts at the same time. They were $21 for the set. Then to be on the safe side I picked up a 3/4 drive socket set for $59. I wasn't sure that my 1/2 inch set would be up to the job. I looked at buying just the tools I would need for the job at Sears but the Slider bar,extention and socket would have been over $60. Of course the craftsman tools look much nicer but I cheaped out. Time will tell how the chinese tools hold up. Plan to scrounge up a nice long piece of pipe in case the bolt tries to give me any trouble. The King Kutter manual recomends keeping your blades sharp. I'll let you know if I can tell any difference. I may take the old blades to the sharpening shop just to see how they do it. I do know that they use a water cooled grinder so I hope that it won't mess up the temper.

Chris

 

[JeffRey30747]

Chris,
If you are replacing the bolts anyway, you may want to line up someone with an acetylene torch just to save yourself some trouble in removing the old ones, but the ones you have may come off easier than I think. Zap 'em with penetrating oil a couple of times a day for few days before you try them and they may come off without much of a problem.
Best of luck, Jeff

 

[Muhammad]

<font color=blue>When I was a kid… after sharpening, my friends’ Dad {God bless his soul} would put the blades on a scale… one on each side {old fashion-looked like the “scales of justice”} to adjust for balance…</font color=blue>

Quick trick I use similar to that, is to hang the blade by the center bolt hole (if there is a center bolt hole), on a nail... comes close enough if you don't have a scale in the barn. /w3tcompact/icons/wink.gif

 

[bgott]

You got me thinking...on a rotary cutter you'd want both blades to weigh the same. You could build a balance scale. Take a board two feet long, stick a nail in each end, drill a hole exactly in the center of the nails, drive a nail into something to hang it on and use that to balance the blades. Just grind a little more off of the heavy one. You wouldn't have to be exact, the first time you bounce one blade off a rock your balance goes to pot anyway.

 

[cedarranch]

I do the same here on mower blades with a center hole. I have a short rod welded to my grinder stand. As for rotary cutter blades I use a bathroom scale. Since they are so heavy, that bathroom scale works great to match the blades.

 

[Hillbilly]

If it was not too much of a hassle changing the blades an individual could have 2 sets of blades...1 for the brush and a sharper set for the grass.

 

[Bird]

Muhammad, for my finish mower blades (hole in center), I do something similar except I use a very small round shafted screwdriver instead of a nail. But since the rotary cutter blades are so different (hole in one end) and so heavy, I have scales in the shop that go to 20 pounds (10# scale and twice around) that I can hang one blade at a time on to weigh them.

 

[patrickg]

bgott,
Seems that if you use a longer board (or whatever) will have a more sensitive device. Also, I wouldn't be to hasty to just drill that thing dead center and start using it as wood can vary considerably in density over even a small distance, at least when you buy cheap stuff like I do. You could literally give it a whorl 3-4 times and see if it favors one end over the other and add some weight to the light end to balance it.
In the olden days when flying gas powered model aircraft (the RC units had tubes- valves for the UK), we used to ballance the props on the high RPM engines (hot rodded). To make a sensitive tester we put a snug fitting shaft through the hole in the center of the prop and let each end of the shaft rest on the up turned edge of a single edged razor blade (carefully leveled). This worked well for even props less than 5-6 inches in total length. Once "micro-ballanced" and then varnished, you could easily detect a small difference in the weight of a coat of varnish or butyrate dope. (A little 600-1200 grit sanding would get it under control.) The Rube Goldbergs among us (I like to include myself in that august group) could easily scale up something from that approach for free out of the junk box or for a couple bucks from the H/W store.


Patrick