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Ideal Blade Tip Speed?

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Allen S.,
I'd welcome more info on the subject!
It just seemed as though the discussion was 'veering for the ditch', so before all the players moved on, I wanted to thank those that participated in the discussion.


Wes H.,
Yes, now that makes a lot of sense -- larger wings on the decks of the newer mowers. As a matter of fact, this afternoon I did some trimming with a push mower and then removed the blade to touch up the edge for tomorrows work, and I noticed that the blade had a MUCH higher/larger wing to it than the Cub blades. It makes good sense that would make more noise as well. Thanks for sharing your observations regarding your experience with the Gator blades too. I will need to look into "how much wing" is built into the replacement #91-321 and #91-322 Oregon blades. Hmmmm..... VERY Interesting!

Lastly, in regards to you downsizing your driven deck pulley by 0.75". If I were to install a likewise 0.75" smaller driven deck pulley (changing the 6.25" to a 5.5" pulley), the math indicates my spindle speed and my blade tip speeds would increase in the neighborhood of whopping 13%! Which equates to resultant blades speeds of 16.5K to 19.1K ft/min.

I'd bet that a 13% increase in pulley rpms would likely still be within the acceptable operating range of the spindles and would improve the performance of the grass cutting & clipping removal tasks.

-- Thanks Guys!
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Ryan Wilke
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I installed a 44A deck with regular blades on my 169. I didn"t like the way it threw the grass out so i installed high lift blades. That helped some but it would windrow to much. I then went to gator blades and the speed up pulley, and that is where i was happy with my mower. Then i rebuilt the 169 engine and it ran at 3000 R P M and i didn"t change it until i mowed the lawn twice. My wife complained that it looked ragged. So i set the R P M to 3500 and installed a spring assist which helped keep the runners from scalping on turns, and it does better than it ever has . My son has a 1180 and he can"t keep up with the 169. So what i am saying is i think it takes a combination of things to get the perfec cut from a 35yo mower.
Luther
 
Ryan,

Sounds like a near perfect ratio for mowing,let us know the results please. I think that 19k is going to show positive results with a 44/50" deck.

Wes,

True about the Gators, great cutting blades in many conditions, but they do tend to leave some green dandelions, and stripping at times. I like the "regular" style blades Oregon offers from spring through June, the switch over to Gators after that when the hotter dryer conditions are prevalent.
 
My commercial Scag ZTR uses a 6" OD clutch pulley, 4.75 driven pulleys and 16" blades. Tip speed in FPM is 22,8012....These mowers are designed to run at full ground speed (10 MPH in this case, although I understand that some of the newer ones are around 13 MPH) on a normal length grass and be able to produce a good looking cut (most of these are used to cut $omeone el$e$ lawn, usually picky you know what$) ... Without the baffle, they also launch grass, rocks and small toads at about the speed of sound.
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Ryan-

<blockquote><hr size=0><!-quote-!><font size=1>quote:</font>

...it seems to me that by having a higher tunnel area would cause a pressure drop in that area, which in turn would reduce the transport velocity (speed) of the passing air & grass, which would reduce the distance the clippings get tossed out the side shoot...<!-/quote-!><hr size=0></blockquote>

A higher tunnel area would result in LESS of a pressure drop than a smaller tunnel area, and this reduces the velocity, distance the grass flies, etc.

19K ft/min. is only about 216 mph, nowhere near the speed of sound at standard sea level. If you got the tip speed supersonic, you'd become hard of hearing in a hurry...
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I put a Kohler Command 18 in my 582, which has something like a 6.5" PTO clutch instead of the 4.5" or so clutch that the tractor would have had originally. I put a 50" deck on it once, and it was deafening, but it sure cut nice. If it really rains tomorrow like it's supposed to, I'll probably find myself calculating what the blade tip speed for that setup was.
 
I looked at the newest MTD Cubs today in a box store to see how the decks were formed. What I saw was maybe 38"-40" wide, but formed like 2 doughnuts next to each other, without too much interconnection towards the rear. My thought on high tunnels is the blade sucks the grass UP, then around. Does one need a place to momentarily store the compressed air the vacuum made??? Just an <font size="-2">off the wall</font> thought.
 
Allen - The deck makers a while back had openings on the top to let the air pressure out , did you notice any on those ?
It makes sense to have an outlet for the pressure since it can't forum a vacuum with a closed container. All that lift has to go somewhere and the blades are directing it up not out the chute.
 
<blockquote><hr size=0><!-quote-!><font size=1>quote:</font>

By Gerry Ide (Kide) on Thursday, June 17, 2010 - 01:42 pm:
My commercial Scag ZTR uses a 6" OD clutch pulley, 4.75 driven pulleys and 16" blades. Tip speed in FPM is 22,8012....<!-/quote-!><hr size=0></blockquote>

WOW! THAT IS CRAZY FAST!!
Hey, wait a cotton-pickin' minute,,,, 22,8012 ft/min? Wha??
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Gerry,,,,Ok, let's see the math on how you obtained that value.
What rpm does your ZTR mower engine run at anyway?


Jim D.,
I agree, I think a 13% increase would be good to try, but I looked around our sponsor sites and I wasnt' able to locate a 0.75" undersized, 2-sheaved center pulley for my 42" deck. I did find a smaller (4") pulley for the 44" and the 50" deck at CCS.


Allen S.,
I think I can get close to the shape of three doughnuts by going with some tighter & taller shrouding, like Dennis F. installed under his 38" deck over on the main forum on 6/14th.
Interesting info on the link to the BETTER walk behind mower. blades run at 19K ft/min. and the deck has deep baffling (shrouding) and a tunnel exit chute..... Very interesting!


Matt G.,
Thanks for chiming in, I always enjoy hearing your opinions. I hope you do calculate your blade tip speed with your hot-rodded 582 and bring your findings back here to share!
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Ryan Wilke
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Ryan, Gerry is a very precise individual.
He meant to type 22,801.2 ft/min. Cause he used his calculator instead of slide rule which is only good to 3 decimal places!
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Sigh... let's try this again, including the inch to foot conversion... (I'm using PI*blade diameter/12*RPM*pulley stepup ratio) or (16*3.1417/12)*3600*1.26 which is......ta da.. (yer gonna love this, ANSI) .... 19001.0016 FPM
 
The "Better" uses Kevlar belt. I bought one for my 42" CI deck once and Don Vogt told me that Kevlar belts build up to much heat , so it's still in the cardboard sleeve.
 
KentucK:
I'm not sure what the Scag's belt is made of, I thought it was gold... ($67.00 the one time I've had to buy one..)

Allen:
Google calc, cut n' paste, I didn't catch the in/ft mistake and it LOOKED like 22,000 to me (eye's musta been blurry from all the sweat, I'd just come inside from a project in the barn)
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Kid<sub>e</sub> - I didn't know you were a cattle breeder ...

One time I thought about building a mower that was all fluid drive. But then I figured it'd be to hard to keep the fluid cool. Cut down automotive rear with hydraulic motor input and high speed hydraulic motors on the blades.
I hate belts and chains !
 
Maybe our blade tip speed calculations would be more precise if we used this for Pi:

3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679
8214808651328230664709384460955058223172535940812848111745028410270193852110555964462294895493038196
4428810975665933446128475648233786783165271201909145648566923460348610454326648213393607260249141273
724587006606315588174881520920962829254091715364367892590360011330530548820466521384146951941511609...

Ryan Wilke
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