Do you mow at 540

Hooked_on_HP · Jul 30, 2006

I have a KK 72in rear dis. RFM. In the spring it mowed great. As the crabgrass started coming on it started leaving balls of grass behind and I had to use a lower gear. When I got to looking at the balls of grass it looks almost pulverized, not a blade of grass over 1/2 in. I know the crabgrass holds a lot of moisture and is harder to mow but I started wondering if the blades could be going to fast. When I'm at 540 PTO (2400 rpm) this mower sounds like a hovercraft. I tried mowing another part of the yard at 1800 rpm. I still had the balls of grass but the mower didn't bog down any and I could go up a gear. I checked all the paper work and it is a 540 pto. Do you always mow at 540 PTO.
Bill

PineRidge · Jul 30, 2006

540 RPM PTO speed is like 2600 Tach. RPMs on our TC-40D. However I tend to run the RFM at about 2K RPM with good results.

I don't mow wet grass though.

5030 · Jul 30, 2006

I don't mow grass, per 'se at least not what you mow. I mow hay and though my mower is rated at 540 rpm, I most always run it in the torque range of my tractor which equates to around 450 rpm.

I never run my lawn tractor at full speed either. About 1/2 throttle seems to do a better job and saves some fuel too.

Mowing a broadleaf weed like mature crabgrass in advanced stages would probably necessitate the need for a high lift blade to get it up and out from under the mower deck.

frank_f15 · Jul 30, 2006

When i use the RFM i always run at 540 PTO speed( on my tractor 2600 RPM) and depending on the height of the grass and moisture content i will get cumping. My theory is run at 540, for the best cut

5030 · Jul 30, 2006

Frank:

Don't you "mow" snow more than grass???

Doc_Bob · Jul 30, 2006

PTO 540 is 2200 RPM on my TN70A. I run at 2200 rpm.
Bob

greg_g · Jul 31, 2006

I believe the engineers when they say blade tip speed is what cuts grass. That, and sharp blades of course. If their design (blade tip) speed is achieved at 540 PTO rpm, then that's where I set the throttle. On my KAMA that's about 2250 engine rpm. I apply the same logic to my rotary cutter. Same for the PTO driven spreader too. Those engineers calculated spread patterns based upon 540 rpm. So if I'm to go by the spread charts in the owner's manual, I'd best be turning 540 PTO rpm

//greg//

TwinWillows · Jul 31, 2006

I find that 540 PTO cuts well on our TC40DA. Thas't right @ 2500 engine RPM.

Bird · Jul 31, 2006

Apparently, using a lower speed works for some people, but I always ran my tractors at the 540 PTO speed, whether mowing with a brush hog, finish mower, or haybine or tilling with the tiller or baling hay with the baler.

MrSteve · Jul 31, 2006

I run mine at 540 (around 2300rpms) "most of the time", but if I know i am going to hit some heavy stuff (where the horses do their business), I will run at around 2500rpms to get the extra blade speed so when I hit that thick stuff I won't go below the 540 pto speed.

have_blue · Jul 31, 2006

I have a Woods BB72. I cut at around 425 PTO RPM. I have found that 540 usually shreds the grass and makes brown fluff balls that stay in the field forever. 425 cuts the grass and weeds cleanly, and the plants fall over and lay flat, where they quickly decay. 540 makes a lot of whanging and banging noise as the weeds grind against the deck. At 425, all I hear is a nice swooshing sound.

I always take 15 minutes to touch up my blades every time I mow, and sharpen them truly sharp. At 425, they stay sharp, and only need a touchup next time. At 540, they start dulling out real quick, and look pretty sorry by the time I'm finished.

I don't think rotary cutters were designed to grind and shred thick grass and weeds like a mulching mower. That takes entirely too much power, and can really heat up the tractor engine and mower's gear box.

greg_g · Jul 31, 2006

have_blue said:
I cut at around 425 PTO RPM. I have found that 540 usually shreds the grass and makes brown fluff balls that stay in the field forever.

Have you considered that your tach may not be reporting RPMs correctly?

//greg//

Soundguy · Jul 31, 2006

I also run my tach at the place where it gives me 540 pto rpm.. if perhaps not a few more rpm.. but never less.

Soundguy

greg_g said:
I believe the engineers when they say blade tip speed is what cuts grass. That, and sharp blades of course. If their design (blade tip) speed is achieved at 540 PTO rpm, then that's where I set the throttle. On my KAMA that's about 2250 engine rpm. I apply the same logic to my rotary cutter. Same for the PTO driven spreader too. Those engineers calculated spread patterns based upon 540 rpm. So if I'm to go by the spread charts in the owner's manual, I'd best be turning 540 PTO rpm

//greg//

Soundguy · Jul 31, 2006

have_blue said:
I always take 15 minutes to touch up my blades every time I mow, and sharpen them truly sharp. ...I don't think rotary cutters were designed to grind and shred thick grass and weeds like a mulching mower. That takes entirely too much power, and can really heat up the tractor engine and mower's gear box.

IMHO.. rotary rough cut mowers are not meant to have 'really sharp' blades.. but rather almost a 32nd flat... etc.

soundguy

have_blue · Jul 31, 2006

greg_g said:
Have you considered that your tach may not be reporting RPMs correctly?

//greg//

That would be unusual on 2 different tractors.

3RRL · Jul 31, 2006

Same here...always at 540 pto rpm. I may accomplish this by using one or the other pto range (depends on cutting conditions) but the pto rpm is always 540. I also read a recent post written here on TBN where it doesn't hurt to spin faster than 540. I haven't tried that personally, since my results have been adequate so far.

have_blue · Jul 31, 2006

Soundguy said:
IMHO.. rotary rough cut mowers are not meant to have 'really sharp' blades.. but rather almost a 32nd flat... etc.

soundguy

Well, you're correct that 1/32" flat is usually recommended. But rotary cutters usually cut heavy stuff, which I knocked out years ago. All I cut now is grass and light weeds. Since I use it like a big lawn mower, I sharpen it like a lawn mower. I highly recommend sharp blades and lower RPM. Works great for the past 5 years.

Turkeyman · Aug 1, 2006

I cut at 1500 RPM with my MX6 and my Brown tree cutter, but if I want the best results I use the PTO speed of 2500 rpms. At 1500 rpm I can cut thru 5 ft tall Johnson grass ( looks like corn in a field).

Neophyte · Aug 1, 2006

Turkeyman said:
my Brown tree cutter

How do you like your Brown Tree Cutter? Do you have any pics of it in action or the aftermath? We were thinking about getting one for our Ford TW30 (160HP). I'm not sure they are rated for this type of HP since the largest listed on the Brown site is 100HP.

PineRidge · Aug 1, 2006

have_blue said:
I always take 15 minutes to touch up my blades every time I mow, and sharpen them truly sharp.

I happen to catch the highlights of your post Bob and the way that I 1st interpreted it thought that you were touching up your blades with paint after each mowing. Thought to myself, "Man wish I had that kind of diligence." Then the true subject matter of what you were saying hit me. Boy did I feel foolish!