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Tool Talk Discussion Forum

Multi Blade Finishing Mower

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Richard

10-13-2003 04:10:38




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I have a project that I'd like to kick off that will consist of building a 4 bladed finishing mower, hyd. driven (Wheels and Blades). The power plant is a 135hp 4 cylinder FZR750 Engine.
The center of the mower will be 4' wide and will have a 24" floating wing on each side of it.

With that said, I have to select pumps and motors, and to do so, I need to know what the normal Tip speed or RPM is of a typical finishing mower. Does anyone have suggestions or advice on this project?

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HJP

10-17-2003 20:00:17




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 Re: Multi Blade Finishing Mower in reply to Richard, 10-13-2003 04:10:38  
HAVE FUN ,BUT IF YOU DO NOT USE QUALITY PARTS YOUR GOING TO HAVE A 100+ HP BLENDER,BE SAFE.
MOST FINISHING MOWERS RELIED ON TORQUE. THATS WHY A 30 HP DIESEL WILL HANDEL A 72 INCH MOWER .ALTHOUGH THE FZR WAS ONE OF THE BEST AT THE TIME ITS MAX TORQUE WAS OVER 4500 RPMS ,WELL OVER THE DESIGN CAPACITY OF ANY INDUSTRAIL GEAR BOX THAT RELIED ON SPLASH LUBRICATION OF GEAR OIL.
LUGGING THE ENGINE WILL CAUSE MAJOR OVER HEATING ON AN ENGINE THAT RELIED ON CONVECTION/AIR COOLING IN ADDITION TO LIQUID. USING THE TRANS IS A MUST BUT I DO NOT THINK THE MASS/BLADE SPEED RATIO WILL GET YOU OUT OF SECOND GEAR.
ALTHOUGH THE SOUND OF A FZR AT 13,000 RPMS, THE WHIRRING OF BLADES,THE FLASH OF AN VANCE&HINES PIPE AND THE SMELL OF MINCED GRASS WILL HAVE JESSE JAMES LOOKING TO GIVE YOU SOME NEW TOOLS!!!!! !!!!! !!!!! !!!!! !!!!! !!!!! !!!!! !!!!! !!!!! !!!!! !!!!! !!!!! !!!!! !!!!! !!!!! !!!!:>

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Bob

10-13-2003 12:44:18




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 Re: Multi Blade Finishing Mower in reply to Richard, 10-13-2003 04:10:38  
I assume you'll be driving the hydraulic pump off the chain sprocket, as most pumps have a fairly low RPM at which they will survive, as opposed to the RPM this engine normally turns. You'll need to beef up the cooling system a bit, since you won't have a lot of motion pushing air through the radiator. You'll likely need a larger radiator and a fan pushing/pulling air through it. In a mowing environment you'll also need to make sure you keep good air filtration at the carbs. Cool idea, keep us posted on your progress. By the way, I don't have any idea what blade tip speed is on a mower, but given that you'll be using 12-13 inch blades I'd say you want to run them at least 3600 RPM.

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Bob

10-13-2003 12:55:29




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 Re: Re: Multi Blade Finishing Mower in reply to Bob, 10-13-2003 12:44:18  
Whoops, I blew it! Looks like you'll be using 24" blades. Here's something I found on the 'net regarding blade tip speed:

"there is an ASME spec that says that the the tip of a commercial mower blade cannot exceed 19,000 feet/min, that's it, max. Exceeding this speed can cause all the things I have been reading from you guys (fatigue, stress, etc.) and will create a dangerous situation for operator AND those around the machine (stones, tennis balls, dog bones, etc). I researched this about a year ago and basically came to the conclusion that this is the reason you see so many 22" mowers with Briggs and Scrap Iron engines for sale."

I won't include all of the math here, but with a 24 inch diameter blade, you can turn it 3024 RPM before you exceed 19,000 FPM

By the way, that's just under 216 MPH Blade tip speed.

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Joe Evans

10-13-2003 12:18:16




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 Re: Multi Blade Finishing Mower in reply to Richard, 10-13-2003 04:10:38  
Richard: Go for it! That's how people make fortunes by building a better mouse trap. Call me crazy, but I've been fascinated by how grass gets cut and have pursued over course of my life better ways to mow grass. One type of mower does not do it all. I've wondered...other than mfg, costs, why aren't there multi-edged cutting blades other than the two edge you universally see? A four-edged blade vs a two-edged blade would in effect double the whacks at the grass offering a better cut. Any reason?

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Robert in W. Mi

10-13-2003 14:29:05




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 Re: Re: Multi Blade Finishing Mower in reply to Joe Evans, 10-13-2003 12:18:16  
I've seen "disc" replacements for blades that had four small cutter blades on them. I've heard they work really well. Robert



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Evielboweviel

10-13-2003 10:20:19




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 Re: Multi Blade Finishing Mower in reply to Richard, 10-13-2003 04:10:38  
from woodsonline.com
90in 3 spindle
Blade speed 2,012 RPM 16,265 FPM tip speed
Gearbox ratio 1.76:1 Tractor PTO speed 540 RPM



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Jim WI

10-14-2003 11:06:12




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 Re: Re: Multi Blade Finishing Mower in reply to Evielboweviel, 10-13-2003 10:20:19  
One of KingKutter's web pages gives some tip speed information for their mowers along with the blade length. From that you can derive the RPM at the blade spindle.

For example, they move their 24" blades (RADIUS = 1') at a tip speed of 16,956fpm.

RPM = TIP_SPEED / ( 2 * PI * RADIUS )

RPM = 16,956 / ( 2 * 3.14 * 1 )

RPM = 2700

(The fact that it works out to exactly 2700rpm tells us that KK used a PI value of 3.14 to calculate the tip speed based on the rpm.)

Keep in mind that there is usually a non-unity ratio on the belt-drive as well as in the gear box.

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Ron from IL

10-13-2003 08:13:22




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 Re: Multi Blade Finishing Mower in reply to Richard, 10-13-2003 04:10:38  
Richard,

I'd find someone who has a finishing mower, and figure the gearing of the gearbox. I don't know if it's 1/1 or geared up slightly. I'd turn the PTO by hand, and note the revolutions per turn of the blades. A typical PTO turns at 550 rpm, so it'd be a simple thing to calculate after determining the gearing.

Good luck!

Ron



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