Can someone explain "Blade Tip Speed" please

   / Can someone explain "Blade Tip Speed" please #11  
Re: Can someone explain \"Blade Tip Speed\" please

</font><font color="blue" class="small">( <font color="blue"> Tip Speed being greater, this would make the KK mower the best cut of anyone. Is this correct? </font>

We find a higher quill bearing/housing failure rate in mowers with the highest BTS. --Ken Sweet )</font>

Blade wear is another consideration. Running at full RPM, the blades on my 72" Woods really get dull fast. After a 7 acre job, they have long since quit cutting and rely on pure velocity to explode the grass like a Weedeater string. Backing the 540 RPM down to ~450, my blades stay very sharp for 1-2 cuts of my 7 acres of grass and light weeds, and leave a great finish. (It runs much quieter too!) It takes 5 minutes to do a light touch-up sharpening on the machine.

If you're cutting 1-3" brush, I guess you need all the tip speed you can get.
 
   / Can someone explain "Blade Tip Speed" please #12  
Re: Can someone explain \"Blade Tip Speed\" please

PB,

That formula only works if you know the blade RPM. You would have to know it, or you would have to know the gearbox ratio to calculate it. My cutter's manual lists the gearbox ratio, (but not the tip speed) so others may as well.

Funny you mentioned the mach number. I have always believed that the grass breaking mach 1 from being whipped violently is partly responsible for fast blade wear, and certainly for much of the noise and bedlam going on under the deck. /forums/images/graemlins/smile.gif
 
   / Can someone explain "Blade Tip Speed" please #13  
Re: Can someone explain \"Blade Tip Speed\" please

</font><font color="blue" class="small">( That formula only works if you know the blade RPM. You would have to know it, or you would have to know the gearbox ratio to calculate it. My cutter's manual lists the gearbox ratio, (but not the tip speed) so others may as well.
)</font>

That is what I meant. Blade RPM. Not PTO RPM.
I should have made that clear.

I watched a show on the History channel once about engines.
A guy talked about jet engines on commercial airlines are
getting so big and powerfull that the turbine blades are
approaching a tip speed of mach 1. And they weren't sure
what would happen if the tip speed exceeded mach 1.

Tip speed for lawn mowers for home owners are limited.
I have a question into another board to find the limits.
And commercial lawn mowers have higher allowed limits.
I'll post when I find what the limits are.

Pooh Bear
 
   / Can someone explain "Blade Tip Speed" please #14  
Re: Can someone explain \"Blade Tip Speed\" please

First Choice Groming mowers are: FPM is 13700 on the 4ft, 14100 on the 5 ft, 14200 on the 6 ft and 15300 on the 7 ft. At 540 PTO, Blade RPM is 3130 for the 4 ft, 2650 for the 5 ft, 2240 for the 6 ft and 2030 for the 7 ft. We have been selling this brand since the company started and have not had 1 failure on the quill assembly.--Ken Sweet
Email sweet@scrtc.com
 
   / Can someone explain "Blade Tip Speed" please #15  
Re: Can someone explain \"Blade Tip Speed\" please

To get the higher blade tip speed, the gear box has to have taller gears. This would reduce the ability of the mower to cut big thick stuff, right. Kinda like driving around in high gear makes you less able to climb a hill. My thought is that it would be easier to stall a blade geared this way when the going gets tough.

If a guy wants to buy a rotary mower for use as a finish mower then go for max tip speed. If you want to bust some brush, gear it down.
 
   / Can someone explain "Blade Tip Speed" please #16  
Re: Can someone explain \"Blade Tip Speed\" please

<font color="blue">Tip speed for lawn mowers for home owners are limited.
I have a question into another board to find the limits.
And commercial lawn mowers have higher allowed limits.
</font>

Pooh bear,

The maximum blade tip speed for homeowner mowers is 19,000 FPM. This has been the OPEI standards for many yrs. When these products came under the stds of the CPSC a few yrs ago, they used the same std. I remember when the engine rpms were lowered to comply with this std. Quality of cut has suffered since.

TK
 
 

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