blade tip speed is any where from 15,000 to over 19,000 on most ztr's . even with the same motor.
can you increase blade tip speed your self ?
can you increase blade tip speed your self ?
lawn storm
A deck clogging up is usually the result trying to get too much grass through a given designed deck. Increasing BTS can sometimes help but it has been my experience that other factors are involved. Some of those factors are blade depth in the deck, baffling, blade offset and discharge. Most of the problems occur at the left blade, at the verticle point where the rear baffles meet each other and the rear of the discharge opening.
I think that grass blade lift and blade sharpness are as important a part of the equation in achieving a clean cut as BTS. High BTS comes into play as the mower moves faster across the lawn. If you have a mower that goes 5 MPH there will be twice as many chances to cut all of the blades of grass as a mower that is moving at 10 MPH given the same BTS.
Walker mowers have a relatively slow BTS, in the order or 14 to 16,000 FPM, but you never hear of complaints about the quality of cut. Why? Because they are slow moving mowers. Compared to a Dixie or a Hustler they are turtles. The limiting factor in a Walker mower isn't the deck or the BTS, it's the ability of the GHS to handle the larger volumes of grass that moving faster would generate.
Walker mowers have a relatively slow BTS, in the order or 14 to 16,000 FPM, but you never hear of complaints about the quality of cut. Why? Because they are slow moving mowers. Compared to a Dixie or a Hustler they are turtles. The limiting factor in a Walker mower isn't the deck or the BTS, it's the ability of the GHS to handle the larger volumes of grass that moving faster would generate.
Lawnstorm
Do You have a FRONT FLOW CONTROL BAFFLE In Your deck? If Not Put One In, Just look At Others Like Hustler It's Not Hard That Should Help.
John.
Do You have a FRONT FLOW CONTROL BAFFLE In Your deck? If Not Put One In, Just look At Others Like Hustler It's Not Hard That Should Help.
John.
Not that you can't increase blade speed, but since I'm the experimenting "king"
, you could easily run into changing the "resonance" of the deck and the resulting vibrations will make it impossible to stand being next to the machine, even with hearing protection. The easiest way to "attempt"to fix the problem is add another set of blades and run doubles. The added amount of air volume should keep the deck clean under almost any circumstances.......Pete
God and your pocketbook help ya if you do crank it up, throw a blade and injure someone.
Not sayin it can't happen with the designed speed but that type of incident would be covered most times by insurance as long as negligence isn't involved.
If that mower is knowingly cranked and an investigation finds that you did it. Well, you are on your own to defend that one.
Besides that, unless you are a real good engineer I wouldn't even consider it. Like Switchless said, the vibrations could change everything with the deck. The things that worry me are the spindles ability to handle a speed up for. Once that spindle no longer wants to stay, it is leaving at how many feet per minute you cranked it to.
Not sayin it can't happen with the designed speed but that type of incident would be covered most times by insurance as long as negligence isn't involved.
If that mower is knowingly cranked and an investigation finds that you did it. Well, you are on your own to defend that one.
Besides that, unless you are a real good engineer I wouldn't even consider it. Like Switchless said, the vibrations could change everything with the deck. The things that worry me are the spindles ability to handle a speed up for. Once that spindle no longer wants to stay, it is leaving at how many feet per minute you cranked it to.
blade tipspeed is affected a great deal by the original design.
some are direct blade drive. the faster bts ive seen were belt driven.notsayin ive seenum all.also u can run the mower at a little higher rpm to increase bts a little.my kohler command is actually rated 4000 rpm ,but i keep it about 3700 or so.also most motors are set up to drop to the rpm with the best torque under heavy cut.hope i didnt confuse u.
some are direct blade drive. the faster bts ive seen were belt driven.notsayin ive seenum all.also u can run the mower at a little higher rpm to increase bts a little.my kohler command is actually rated 4000 rpm ,but i keep it about 3700 or so.also most motors are set up to drop to the rpm with the best torque under heavy cut.hope i didnt confuse u.
You go screwing around with pulleys and belts and I guarantee you there goes the warantee on that machine.
God forbid there is an accident and an investigation if someone is hurt. You'll be out on a limb then and hung to dry all by yourself.
God forbid there is an accident and an investigation if someone is hurt. You'll be out on a limb then and hung to dry all by yourself.
As some of you may know, my FT job is a mechanical engineer for a large defense co. So I have some cridentials on this subject. For one, the only way a blade would fly out from under the deck is if a part broke off, not the entire blade itself. For instance: spin a basketball on your finger and then remove you finger. It is true that the natural frequency would change with the increase in speed but only because it would amplify the unbalance of the blades. But because there are more than one blade and the unbalances not not necessarily synced the vibration with have more than one mode and increase the complexity greatly. The simplified fomula of rotating an unbalance (which all blades are unbalanced to an extent) is: (m*e*w^2)*sin*w*t
m = the mass of the unbalance (very small in our case)
e = the distance the unblance is from the center (around 9" in our case)
w=the angular velocity of the blade (radians/second)
-Scott
m = the mass of the unbalance (very small in our case)
e = the distance the unblance is from the center (around 9" in our case)
w=the angular velocity of the blade (radians/second)
-Scott
A very interesting question but one that I would only ponder. I would never try and modify the BTS. This can bite you on the following fronts, warranty work, possibly shortening equipment life and least not forget insurance coverage. I would not want to hurt myself or anyone else. I would look into what the manufacture suggests as a way to get around the problem you are having.
Gravely_Man
Gravely_Man
I'm an engineer as well, and agree with Scott. I've thought about doing this to my mowers. You could probably safely increase the BTS with small changes in pulley sizes. Obviously, for spindle life, the higher the RPM's the more critical the balance of the blades.
Never the less, any type of modification of the blade drive-line (including tweaking the engine's RPM's) would exempt the manufacturer of any responsibility if there were an accident or malfunction. Even though its probably not going to significantly effect the likelyhood of either of those. But if you send a golf ball across a street and hurt someone, and they find out you're running a hopped up mower, YOU ARE TOAST!
Never the less, any type of modification of the blade drive-line (including tweaking the engine's RPM's) would exempt the manufacturer of any responsibility if there were an accident or malfunction. Even though its probably not going to significantly effect the likelyhood of either of those. But if you send a golf ball across a street and hurt someone, and they find out you're running a hopped up mower, YOU ARE TOAST!
I've never had a good answer to the question of why manufacturers don't change spindle speeds on different deck widths, when the blade length is different. In other words, the spindle speeds are the same (use the same diameter pulley on both deck and engine), regardless of the blade length. For example, the blade length is 16" (48" deck), or 18" (36" or 52" deck). BTS is inversely related to the length of the blade. So, it would seem to make sense to use a smaller pulley on the spindles for smaller blade length to keep the same BTS.
I've only used a 36" mower, with two spindles. I've been looking at a 48" machine, and I see lower BTS. The 48" machine uses 16 1/2" length blades, not 18" blades like my present machine. Do shorter blades leave more room for air flow, hence acceptable discharge rates? There must be a good reason for the differences. Does anybody have hard facts on the matter, just not "I think."
I've only used a 36" mower, with two spindles. I've been looking at a 48" machine, and I see lower BTS. The 48" machine uses 16 1/2" length blades, not 18" blades like my present machine. Do shorter blades leave more room for air flow, hence acceptable discharge rates? There must be a good reason for the differences. Does anybody have hard facts on the matter, just not "I think."
BTS is DIRECTLY related to the length of the blade. I don’t know if you meant to say “inversely” or not. For instance, if a manufacturer uses the same pulley sizes (reducing inventory and costs) on all their decks, then for the same engine RPM’s, the decks with the longer blades will have the higher BTS. Obviously longer blades involve more torque. Higher horsepower engines aren’t for more speed, they produce higher torque to maintain their rated RPM’s under heavy loads.
Not being involved in deck design, I can’t say, but for cutting the same load (density of grass under the deck), the combination of the depth of the deck, baffle design, blade lift and length are important just like the rotational speed. Toro looks like they’re at least paying attention to those combinations with their formed decks, but I’m not that impressed with their product. Then too, even if there is an optimum design, it’s not necessarily “optimum” for different sizes. So to keep fabrication costs from skyrocketing, manufacturers will go with a “good” design that works for many sizes, like vertical sides and a flat top. It's always about the money.
Not being involved in deck design, I can’t say, but for cutting the same load (density of grass under the deck), the combination of the depth of the deck, baffle design, blade lift and length are important just like the rotational speed. Toro looks like they’re at least paying attention to those combinations with their formed decks, but I’m not that impressed with their product. Then too, even if there is an optimum design, it’s not necessarily “optimum” for different sizes. So to keep fabrication costs from skyrocketing, manufacturers will go with a “good” design that works for many sizes, like vertical sides and a flat top. It's always about the money.
Roger wrote:
I've never had a good answer to the question of why manufacturers don't change spindle speeds on different deck widths, when the blade length is different.
Some manufacturers do. Exmark and Dixie Chopper both maintain a BTS close to or about 19,000 FPM regardless of blade size. I am sure Hustler does but I've never checked. The only mower I've ever checked into that doesn't maintain a consistent BTS is Walker.
I've never had a good answer to the question of why manufacturers don't change spindle speeds on different deck widths, when the blade length is different.
Some manufacturers do. Exmark and Dixie Chopper both maintain a BTS close to or about 19,000 FPM regardless of blade size. I am sure Hustler does but I've never checked. The only mower I've ever checked into that doesn't maintain a consistent BTS is Walker.
Sorry - correction noted. I intended to relate BTS to pulley size. The larger the pulley on the deck, the slower the spindle speed, hence the lower BTS for the same length blade.
Your point of all the other factors is well made. If BTS were the only factor, BTS would be more consistent across different mowing decks. Using common parts for different mowing decks is an advantage. From what I've seen on this board, BTS is given too much emphasis. Too many other factors play a role in quality of cut, mowing speed, discharge, etc.
Your point of all the other factors is well made. If BTS were the only factor, BTS would be more consistent across different mowing decks. Using common parts for different mowing decks is an advantage. From what I've seen on this board, BTS is given too much emphasis. Too many other factors play a role in quality of cut, mowing speed, discharge, etc.
Concerning blade tip speed on different width decks:
JD for example uses the same spindle pulleys, but if you check, the engine drive pulley size to the deck drive pulley size ratio is different:
These are the two pulleys that affect blade tip speed and spindle rotations per minute: = It does not matter one iota what size the spindle pulleys are as long as they are the same so all blades are going the same speed - It is the drive train setup between the engine and deck that sets up the speeds.
And I have found that some decks work well with lower tip speeds, go too fast, and air packs or does something and the airflow is all screwed up and the discharge gets screwed up etc.
If the mower mows well - leave it alone.
Thanks, Brad
JD for example uses the same spindle pulleys, but if you check, the engine drive pulley size to the deck drive pulley size ratio is different:
These are the two pulleys that affect blade tip speed and spindle rotations per minute: = It does not matter one iota what size the spindle pulleys are as long as they are the same so all blades are going the same speed - It is the drive train setup between the engine and deck that sets up the speeds.
And I have found that some decks work well with lower tip speeds, go too fast, and air packs or does something and the airflow is all screwed up and the discharge gets screwed up etc.
If the mower mows well - leave it alone.
Thanks, Brad
Tell me what kind of doubles you are running and what pattern you have them in. There is a very good chance you can correct your problem if you luck up and find the right combo.
Changing BTS may or may not help. Air curculation is what dictates these problems. Blade shapes, designs and offsets cn make a dramatic change in how the air circulates. So can a flow control baffle. So for those reasons I ask you where-abouts it the deck clogging? Where does it build up the most and the least, ect? I have toyed so much with blades that I really feel I can help you with a real good description.
Also, remeber if you must change the BTS, make a very minor change to the engine pulley. The reason I say this is you must think of it as a 10 speed bicycle because changing the gearing is what you are doing. Increasing the size of the pulley will increase both the BTS and the load on the engine. So you'll trade off some power and it will bog easier in certain conditions. A better way to increase the BTS is to take it to the dealer and let them adjust the engine RPM's just a bit higher.
Trained mechanical engineer here also. Changing blade tip speed is easily done. Think of it in terms of drive pulley (on the power supply or engine) and driven pulleys (on the blade spindles). You can increase BTS in 2 ways by playing with these pulleys: 1) Make you drive pulley a larger diameter 2) Make all your driven pulleys smaller diameter. Naturally, the belt length will likely need to be changed once any of these diameters is changed. Please note that only MINIMAL diameter changes are necessary to achieve dramatic results. Also note that it takes more power turn blades at this higher speed. For example, if you have a 25hp motor that turns blades at a tip speed of X and barely had enough power to do this and you increase the BTS to 1.25(X), you now have amplified how underpowered the engine is and will work it to it's death. It's just like gearing in a truck. If your truck has a hard time pulling a certain hill in drive ratio (1:1) it will really stuggle in an overdrive ratio such as (.75:1). I mean if your truck is running out of power climbing a hill don't you downshift to a lower gear rather than upshift to overdrive? Changing pullies or gear ratios (same thing) effects the way an engine is allowed to deliver the power it has available. Got it? I have done this on an old single blade 38" rider with great results. Was able to run engine at 1/2 - 3/4 throttle instead of wide open and still had more BTS than before the change. As was stated above - a blade will not sling out from under a mowing deck as a result of increasing it's tip speed alone. They will tend to fall straight down. If it is out of balance enough to come out from under the deck, it was unsafe to begin with before you sped it up. This is pure physics - the spinning basketball analogy above describes it perfectly.
Blade tip speed is real important when your cutting Bahai grass down south. My Scag 48" will miss so much of it you'll have to run over it 3 times and it's only rated at 6.7 mph. My 50" Chopper with the high BTS will generally get all of it........unless it's extremely dry.....then nothing works. My 72" Chopper with the 24" blades will usually get all of it as long as the blades are sharp.
I've said this before and I'll say it once more. I feel like all the mower manufacturers are up north......they test everything on cool season grass which cuts so much easier than warm season stuff.........you might have the more severe clumping problems but we have some tough grass to deal with. Would love to see a mower designed specifically for our neck of the woods and our grass type.
I've said this before and I'll say it once more. I feel like all the mower manufacturers are up north......they test everything on cool season grass which cuts so much easier than warm season stuff.........you might have the more severe clumping problems but we have some tough grass to deal with. Would love to see a mower designed specifically for our neck of the woods and our grass type.
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
