Rotary cutter bladt tip speed?

[Richard]

This has just become an eye opening spec to me after using a borrowed tractor/mower...

We used a 7' mower so for no other reason than that, I using for my example below, HD 7' mowers of these brands...(my real goal is to get a 15')

Woods 8400 7' HD mower, BTS 16,000 fpm
Bush Hog 307 7' HD mower, BTS 11,875 fpm
Brown 684, 7' HD mower, BTS 17,803 fpm

I presume these all use a 540 pto, so given their input could be the same tractor, is one able to make any conclusions based on fpm alone?

Pros/cons?

1. Would the Brown mower be better in "grass" since it has a higher bts, or is it the opposite and the Bush Hog would be better in "grass"?

2. Seems to me, this is all done via gearing, as such, I'd expect in thick stuff, the slower bts to have more power behind it so it wouldn't bog down?

When one is looking at a mower, is this the first spec you might want to look at, after size & duty rating?

I never ever thought about bts, I always presumed for a given size, they'd all be the same.

The Brown we borrowed... while using it, one thing I noticed that is now clear (given it's bts)... it really chopped things up. When I ran over sapplings, small cedar trees... they simply came out the other side as toothpicks. VERY unlike our cutter on our IH-444. Had I run over the same items, those items would have shaken that cutter to smithereens and come out the backside as hacked up stalks, instead of shards.

While cutting I started to get the gut feeling that this mower was cutting MUCH faster (bts) than our cutter, but frankly, I attributed that to the IH-444 probably not getting up to PTO speeds on the tach (old & tired) and the NH we were using being fresh & strong.

Now, I realize there was more going on with the gearing of the cutter themselves.

I'd love to learn more about the pros/cons of BTS when used on same sized mower/tractor.

 

[daTeacha]

Oh boy, this could get interesting.

The BTS will affect the quality of your cut. On grass with a lawn mower, faster BTS usually gives a nicer cut for three reasons -- an effectively slower "feed" rate (there are more mower blade/grass blade impacts per unit of forward travel), more "lift" pulling the grass up into the blade, and more velocity applied to the cuttings to throw them out of the way of the cutting action. With heavier stuff, you will get the first and third benefit, but the second one is not of much consequence.

Having a lower BTS will increase the amount of torque acting at the center wheel of your mower, but whether or not this will translate to more force at the tips of the blades will be a little confusing. The faster turning center hub will give more momentum to the blades and more "centrifugal force" to keep them radial, but there will be less force turning the base of each blade when it hits something substantial. I'll let someone else do the math to figure out the optimal relationship between blade RPM and horsepower.

You also have to consider the potential damage caused when a blade hits a rock or other object. Will a faster turning blade tend to shatter quicker than the same blade moving slower?

I would tend to go with a faster mower for grassier areas and a slower one for brush, saplings, and other truly rough cutting jobs, but that's primarily a gut reaction.

 

[Richard]

I've never heard of Funk, but I'm originally from Hamilton, near Cincy.

 

[daTeacha]

Funk is about 1.5 miles west of Blachleyville and 6 miles north of Big Prairie. We have a general store/gas station/sheriff's outpost/deer checking station, an Amish sawmill, and about a dozen houses in town. I live in the 'burbs.

 

[Richard]

Sounds MUCH like where I live now, in "Greenback"

 

[Soundguy]

For brush cutting.. and 'mass' pasture maintenance.. like a 10 or 15 or 20' mower might be doing.. first 2 things I look at are price and durability.

Heck.. I have a 15' mower.. and don't know the BTS.. never looked it up.. don't care.... It knocks saplings and brush over fine. Just happens to cut pasture grass and briars as well.

If I owned a golf course.. I might check the BTS on my 'finish' mower... but for a rough cutter that doesn't even use sharpened blades.. i think BTS is more like 'chrome'...

Soundguy

This has just become an eye opening spec to me after using a borrowed tractor/mower...

We used a 7' mower so for no other reason than that, I using for my example below, HD 7' mowers of these brands...(my real goal is to get a 15')

Woods 8400 7' HD mower, BTS 16,000 fpm
Bush Hog 307 7' HD mower, BTS 11,875 fpm
Brown 684, 7' HD mower, BTS 17,803 fpm

I presume these all use a 540 pto, so given their input could be the same tractor, is one able to make any conclusions based on fpm alone?

Pros/cons?

1. Would the Brown mower be better in "grass" since it has a higher bts, or is it the opposite and the Bush Hog would be better in "grass"?

2. Seems to me, this is all done via gearing, as such, I'd expect in thick stuff, the slower bts to have more power behind it so it wouldn't bog down?

When one is looking at a mower, is this the first spec you might want to look at, after size & duty rating?

I never ever thought about bts, I always presumed for a given size, they'd all be the same.

The Brown we borrowed... while using it, one thing I noticed that is now clear (given it's bts)... it really chopped things up. When I ran over sapplings, small cedar trees... they simply came out the other side as toothpicks. VERY unlike our cutter on our IH-444. Had I run over the same items, those items would have shaken that cutter to smithereens and come out the backside as hacked up stalks, instead of shards.

While cutting I started to get the gut feeling that this mower was cutting MUCH faster (bts) than our cutter, but frankly, I attributed that to the IH-444 probably not getting up to PTO speeds on the tach (old & tired) and the NH we were using being fresh & strong.

Now, I realize there was more going on with the gearing of the cutter themselves.

I'd love to learn more about the pros/cons of BTS when used on same sized mower/tractor.

 

[Farmwithjunk]

This has just become an eye opening spec to me after using a borrowed tractor/mower...

We used a 7' mower so for no other reason than that, I using for my example below, HD 7' mowers of these brands...(my real goal is to get a 15')

Woods 8400 7' HD mower, BTS 16,000 fpm
Bush Hog 307 7' HD mower, BTS 11,875 fpm
Brown 684, 7' HD mower, BTS 17,803 fpm

I presume these all use a 540 pto, so given their input could be the same tractor, is one able to make any conclusions based on fpm alone?

Pros/cons?

1. Would the Brown mower be better in "grass" since it has a higher bts, or is it the opposite and the Bush Hog would be better in "grass"?

2. Seems to me, this is all done via gearing, as such, I'd expect in thick stuff, the slower bts to have more power behind it so it wouldn't bog down?

When one is looking at a mower, is this the first spec you might want to look at, after size & duty rating?

I never ever thought about bts, I always presumed for a given size, they'd all be the same.

The Brown we borrowed... while using it, one thing I noticed that is now clear (given it's bts)... it really chopped things up. When I ran over sapplings, small cedar trees... they simply came out the other side as toothpicks. VERY unlike our cutter on our IH-444. Had I run over the same items, those items would have shaken that cutter to smithereens and come out the backside as hacked up stalks, instead of shards.

While cutting I started to get the gut feeling that this mower was cutting MUCH faster (bts) than our cutter, but frankly, I attributed that to the IH-444 probably not getting up to PTO speeds on the tach (old & tired) and the NH we were using being fresh & strong.

Now, I realize there was more going on with the gearing of the cutter themselves.

I'd love to learn more about the pros/cons of BTS when used on same sized mower/tractor.

Those Brown mowers are considered to be about the best there is at handling REALLY tough mowing conditions. I thought it was interesting it has the highest blade speed.

I'm all the time telling people how my Bush Hog 286 cutter cuts "cleaner" than my Woods BB840 or the old Woods MD172 I had. Then I see Bush Hog with the slowest blade speed. Interesting also.

I'm comparing totally different models too.

 

[john_bud]

For higher BTS, the damage to the equipment might be worse when you hit a buried steel pipe, large rock, stump etc. It would sure have more whacks before the clutch could be stomped or the 3pt raised.

It probably has a greater hp requirement (torque really) to get the blades up to speed and keep them there. It's like being in 5th gear vs 4th gear. The engine might bog down easier in heavy weeds, but if you start with a big enough tractor...no issue.

I did try and maximize several things when buying my last cutter. BTS was one, gear box HP capacity, overall weight and stump jumper weight the others. I wanted the greatest rotating mass, to dampen the shocks of hitting and cutting a larger tree.

It does sound like Richard got his own questions answered. For his application, higher BTS seems to make the equipment perform better.

jb

 

[Richard]

Anybody know if we put a conveyor under the mower with the highest BTS, if it would take off or not?

 

[1bush2hog]

Seems to me if the blade is turning faster and has the torque to go with it, it should cut anything (that will cut) better than a slower blade with the same amount of torque-

With that being said, what about the gearbox and the ratings? Is the Brown BTS based on 120HP which is what the gearbox is rated at? Is the BTS slower with a 65HP tractor at 540rpm than with a 90hp tractor at 540rpm?

Farmwithjunk - your BH286 BTS is rated at 14,877

"For higher BTS, the damage to the equipment might be worse when you hit a buried steel pipe, large rock, stump etc. It would sure have more whacks before the clutch could be stomped or the 3pt raised. "

Johnbud - Is this true if the slipclutch is properly adjusted?

 

[Fredex]

Is the BTS slower with a 65HP tractor at 540rpm than with a 90hp tractor at 540rpm?
QUOTE]

Nope. Blade tip speed depends purely upon pto rpm, gearbox ratio, and blade radius. HP has no effect on BTS so long as pto rpm remains at 540.
Fred

 

[firemanpat2910]

how many mph in a fpm ? how much difference does it realy make? what % faster is 17803 than 16000? too much math for me. I just want to finish work and go play with my tractor!!!!!!!!!!!!!!!

 

[rozett]

what % faster is 17803 than 16000?

11% faster

how many mph in a fpm

1 mph = 88 fpm so..... 17803 fpm = 202 mph

 

[Richard]

how many mph in a fpm ? how much difference does it realy make? what % faster is 17803 than 16000? too much math for me. I just want to finish work and go play with my tractor!!!!!!!!!!!!!!!

Well, using the bushhog verses the Brown

17,803 fpm / 11,875 fpm is 49.92% increase with the Brown at the same PTO speed!



No wonder it diced everything up a LOT more than the regular cutter we use. I honestly don't think our IH-444 gets to full RPM's, and if that is right, then I'm never using it at PTO rated speeds. (tach doesn't work right, or if it DOES, then I'm right and we're probably 65% of PTO speed)

 

[Richard]

Oops, my apologies, I didn't notice the qualification as to WHICH speeds you were referring to...

 

[Soundguy]

What also needs to be taken into acount is that longer blades will have a higher tip speed.. all else being equal.

soundguy

Seems to me if the blade is turning faster and has the torque to go with it, it should cut anything (that will cut) better than a slower blade with the same amount of torque-

With that being said, what about the gearbox and the ratings? Is the Brown BTS based on 120HP which is what the gearbox is rated at? Is the BTS slower with a 65HP tractor at 540rpm than with a 90hp tractor at 540rpm?

Farmwithjunk - your BH286 BTS is rated at 14,877

"For higher BTS, the damage to the equipment might be worse when you hit a buried steel pipe, large rock, stump etc. It would sure have more whacks before the clutch could be stomped or the 3pt raised. "

Johnbud - Is this true if the slipclutch is properly adjusted?

 

[Farmwithjunk]

Seems to me if the blade is turning faster and has the torque to go with it, it should cut anything (that will cut) better than a slower blade with the same amount of torque-

With that being said, what about the gearbox and the ratings? Is the Brown BTS based on 120HP which is what the gearbox is rated at? Is the BTS slower with a 65HP tractor at 540rpm than with a 90hp tractor at 540rpm?

Farmwithjunk - your BH286 BTS is rated at 14,877

"For higher BTS, the damage to the equipment might be worse when you hit a buried steel pipe, large rock, stump etc. It would sure have more whacks before the clutch could be stomped or the 3pt raised. "

Johnbud - Is this true if the slipclutch is properly adjusted?

Glad to know that about my 286 mower. It'll mow anything a medium duty cutter should as far as brush and weeds, plus does a good job of mowing grass. Real smooth cut in anything.

Gear box ratings are a recommended maximum INPUT hp level. In other words, the biggest tractor you can use. It doesn't take that much power to run it.

A slip clutch doesn't do much to lessen the initial impact when a mower blade strikes, let's say that buried steel pipe. Also, a fair amount of driveline shock goes back through the tractor. That is why the high horsepower recommendation on the Brown, or any of the heavy duty mowers. It's best to have them on a big enough tractor to take what the mower can and will dish out.

One more thing. Take a look at Rhino's heavy duty brush cutters. Their heavy duty equipment is what put them on the map. Good stuff!

 

[chrisjbell]

One more thing. Take a look at Rhino's heavy duty brush cutters. Their heavy duty equipment is what put them on the map. Good stuff!

I'll second that recommendation. My Rhino cutter works great, takes a lot of abuse, and I have *no* idea what the blade tip speed is ;-)...

 

[1bush2hog]

My Rhino cutter works great, takes a lot of abuse, and I have *no* idea what the blade tip speed is ;-)...

If you are interested you can find the info here

TW84

 

[N80]

Gear box ratings are a recommended maximum INPUT hp level. In other words, the biggest tractor you can use. It doesn't take that much power to run it.

I think you're right, but the specs on my JD LX-6 do give a minimum pto hp requirement (22 hp), which seems odd. Under the gear box specs it lists 'hp rating' as 60, which is the max I guess. The BTS is 15,000. Cuts grass pretty cleanly. Its rated a only 1" trees but it breezes through 2" pines, locusts, and plums. I've never tried 3", and probably won't