Rotary Cutter Blade tip speed
- Thread starter RoBoss
- Start date
Welcome to the forum. I am not sure why you are asking? Are you asking about a single, double, or triple spindle? I know that the longer the blade, the slower the tip speed.
Not vital. Typical recommended speed is 540 RPM at the PTO. I will run it a little faster some times, but not often. I will also run it a little slower depending on the situation. If the PTO is to slow for the tractor travel speed you will get an inferior and uneven cut.
There should be a PTO speed gauge on your tractor.
Different tractors will run different Engine RPM to achieve the 540 PTO speed. Many older tractors run at 1750 engine RPM. My Kubota L4330 runs about 2650 to maintain the 540 RPM speed. Your manual should tell you what your engine RPM should be at.
It's not unreasonable to believe the faster the tip speed, the better the cut. Let's say you are looking at a 7' cutter. Models may vary by 2000 rpm +/- in tip speed. If all are 540 input with the same size blades, only difference could be the gear box ratio.
Russell King
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Quoting Bulldog (search site for his posts on this subject_
"When you go to look at the specs on cutters look at the blade tip speed. I wouldn't want one lower than 13,000 feet per min. 15K fpm would be even better. "
"When you go to look at the specs on cutters look at the blade tip speed. I wouldn't want one lower than 13,000 feet per min. 15K fpm would be even better. "
Thanks for all the help. I just noticed that blade tip speed changed between models and sizes. From the replies, it looks like the faster the better.
I'll give you this example from my own cutters.
My Bushhog SQ600 has a tip speed of 12,469 fpm.
My Bushhog 3008 tip speed is 16,345 fpm.
My Bush Whacker T180 tip speed is 16,768 fpm.
Aside from how sharp the blades are there is no real difference in cut quality between the 3008 and the T180. However the difference between these 2 and the SQ600 is like night and day. It's not that the SQ600 cuts bad, it just simply doesn't have the same cut quality of the others. All are driven by 540 pto and if you want to throw deck size in the SQ600 is 5', the T180 is three 5' decks combined and the 3008 is more or less two 4' decks in one.
So, is blade tip speed important? If you want a high quality cut, then the blade tip speed is one of the single most important things about a rotary cutter. if you want to see the difference for yourself cut a few passes with your cutter at the rated pto speed then drop it down to about 1500 rpm's for a few passes. You'll have your own side by side comparison to look at. The only difference between the 2 is the tip speed has changed and I'll bet the slower speed isn't as good as the faster one.
My Bushhog SQ600 has a tip speed of 12,469 fpm.
My Bushhog 3008 tip speed is 16,345 fpm.
My Bush Whacker T180 tip speed is 16,768 fpm.
Aside from how sharp the blades are there is no real difference in cut quality between the 3008 and the T180. However the difference between these 2 and the SQ600 is like night and day. It's not that the SQ600 cuts bad, it just simply doesn't have the same cut quality of the others. All are driven by 540 pto and if you want to throw deck size in the SQ600 is 5', the T180 is three 5' decks combined and the 3008 is more or less two 4' decks in one.
So, is blade tip speed important? If you want a high quality cut, then the blade tip speed is one of the single most important things about a rotary cutter. if you want to see the difference for yourself cut a few passes with your cutter at the rated pto speed then drop it down to about 1500 rpm's for a few passes. You'll have your own side by side comparison to look at. The only difference between the 2 is the tip speed has changed and I'll bet the slower speed isn't as good as the faster one.
85Hokie
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Bulldog nailed your answer, tip speed is huge.
Now you did NOT say if it is a finish mower or brush hog - both are rotary cutters - however, the single blade brush cutter has a "dull" edge and a multi blade mower has a much "sharper" edge. A brush hog will cut (explode is the better word) small limbs and other debris - where as the MMM will cut grass finely. But both will cut better at a higher tip fps. The speed of the tip also has a lot to do with what is hit, on a hog - the speed times the mass of the blade breaks through stuff, where as on a multi-head the speed is used to cut nicely and throw the stuff out the side further.
I am always amazed that people cut at idle on riding lawn mower......grass looks like hell and the bagger doesnt work well.....etc !!!
The PTO to 540 ratio is where they get the tip speed number.
And a sharp blade is mo' better than a dull one! Just look at the turkey you cut on Thanksgiving!
Suprised nobody mentioned supersonic, harmonics blade failure and potential injury.
That is one reason to not exceed reccomended blade speed.
That is one reason to not exceed reccomended blade speed.
Bushhog blades can do and will bend and break. Be prepared mentally for it to happen and know how to turn it off fast.
In working on bushhogs over the years I've seen blades upside down, bent, backwards, upside down, too long, too short, split, cracked, torch-whittled, worn bolts, missing or worn or ground-off key on bolts, loose bolts, missing nuts and washers, and everything in between.
Be cautious especially in buying used iron.
If replacing blades on a used bushhog do not guy replacements based on what you see under the machine---it may be way way wrong. Track down the maker and get a valid part number. There are literally hundreds or more different possible styles and type bushhog blades on the market.
Please post back your continuing experiences so we may all learn.
In working on bushhogs over the years I've seen blades upside down, bent, backwards, upside down, too long, too short, split, cracked, torch-whittled, worn bolts, missing or worn or ground-off key on bolts, loose bolts, missing nuts and washers, and everything in between.
Be cautious especially in buying used iron.
If replacing blades on a used bushhog do not guy replacements based on what you see under the machine---it may be way way wrong. Track down the maker and get a valid part number. There are literally hundreds or more different possible styles and type bushhog blades on the market.
Please post back your continuing experiences so we may all learn.
"Bushhog blades can do and will bend and break."
I was raking hay about 75' off the road when I heard an odd sound like rake teeth going over a bottle. Stopped to check. It was a mower blade from a brush cutter. Probably the county mowing crew flipped one off at some point. 4 inches wide, 18" long, 1/2" thick becomes a missile when loose.
I was raking hay about 75' off the road when I heard an odd sound like rake teeth going over a bottle. Stopped to check. It was a mower blade from a brush cutter. Probably the county mowing crew flipped one off at some point. 4 inches wide, 18" long, 1/2" thick becomes a missile when loose.
Tip speed is proportional with blade length, longer blade, faster speed. Helicopter blade tips are near or beyond supersonic (depending on the design) while the hub is actually turning fairly slow.
Tip speed is determined by diameter turned through by the blade and multiplied by RPM to get you feet/meters per minute. So at 540 RPM, through the gearbox ratio (which varies) and then factor in diameter, you get the tip speed.
If you know the tip speed, you can math out the gearbox ratio.
Rotary cutters don't give the best finish anyway. If you are truly concerned about finish, you are into towed or powered reel mowers. That's like cutting your grass with scissors!
Tip speed is determined by diameter turned through by the blade and multiplied by RPM to get you feet/meters per minute. So at 540 RPM, through the gearbox ratio (which varies) and then factor in diameter, you get the tip speed.
If you know the tip speed, you can math out the gearbox ratio.
Rotary cutters don't give the best finish anyway. If you are truly concerned about finish, you are into towed or powered reel mowers. That's like cutting your grass with scissors!