Blade tip. speed increase

[sgtsampay 117]

Hello all. I have a 36in rear discharge in nice shape. It's going on my 13hp rig so I know the power will be there. The trouble is how can I decrease the blade speed via the pulley on the deck that connects to the mule drive. Or do you think it would be better to increase the pot pulley somehow. Any ideas. Thanks. I do know in the past some have done mods to increase the tip speed but if you had to do it again any easier way?

[953 nut 51,511]

From what I am reading here it sounds like you haven't mowed with this yet. Presuming the old 10 HP had a PTO clutch on it I would start by using it on the new engine. Seems to me that    did a real good job of engineering their tractors and that has to be a good starting point. The bigger the PTO drive pulley the faster the tip speed will be, but with a rear discharge mower I don't know if you would find it advantageous.   

[can whlvr 991]

why do u want to decrease the speed,you can put it on the outer pulley on the pto

[sgtsampay 117]

Hmm. Correct I haven't used this deck yet this year. My reasoning for high blade tip[ speed was so I can mow at any fast pace I want as long as the ground isn't rough. Am I creating extra work for nothing if this isn't needed?

 

Also, I meant increase speed. Your right decreasing wouldn't be need. LOL.

[bmsgaffer 2,043]

Personally, I dont think the WH decks can handle much blade tip speed increase. If you look at the commercial mowers that have higher blade speeds their decks are a thicker material and the spindles are huge. (I have an early 90's Snapper professional walk behind. It has some serious blade-tip speed)

 

If you increase the speed of the blades the wind resistance increases by a larger amount and will require more HP. With 13 hp on a 36" deck you should have plenty to spare so thats not an issue, but i do worry about the reliability and safety of it. People tweak decks all the time by hitting something the way they are designed now. If you increase blade speed AND travel speed then you will probably kiss the deck good bye if you hit a large branch.

 

But, if you still want to do it, as I think I saw that you were planning to mow semi-commercially with it, then your best bet will be to find an electric PTO with a larger pulley that you can retrofit onto the horse. Might take some trial and error. (And I would only do it by a very small amount). But you will also have to watch out for belt profile as you may cause excessive wear if the pulley profile doesnt match the belts'. 

Edited April 11, 2015 by bmsgaffer

[tbarnhart 240]

I increased mine by increasing the size of my pto pulley. I have a 5.5 in. pulley bolted on which puts my blade tip speed a good bit faster than stock. It does allow me to cut in 3 hi most of the time and still get a decent cut. If it's rough or the grass is real heavy, I'll slow down to 2 hi. I wouldn't think a smaller pulley on the deck would work as well, more chance of the belt slipping on a smaller pulley.

[daveoman1966 3,586]

I may have just the thing you want, if increasing tip speed is your goal. This is a double-pulley for the center spindle and it is only about 3" diameter on the TOP and BOTTOM of it. Usually, the top section is 4" or so, and the lower V pulley is 3" (estimates). This pulley is the SAME on top and bottom. Here is a pic...

For more info, send an email to me here:

daveoman@windstream.net

Edited April 11, 2015 by daveoman1966

[sgtsampay 117]

Personally, I dont think the WH decks can handle much blade tip speed increase. If you look at the commercial mowers that have higher blade speeds their decks are a thicker material and the spindles are huge. (I have an early 90's Snapper professional walk behind. It has some serious blade-tip speed)

 

If you increase the speed of the blades the wind resistance increases by a larger amount and will require more HP. With 13 hp on a 36" deck you should have plenty to spare so thats not an issue, but i do worry about the reliability and safety of it. People tweak decks all the time by hitting something the way they are designed now. If you increase blade speed AND travel speed then you will probably kiss the deck good bye if you hit a large branch.

 

But, if you still want to do it, as I think I saw that you were planning to mow semi-commercially with it, then your best bet will be to find an electric PTO with a larger pulley that you can retrofit onto the horse. Might take some trial and error. (And I would only do it by a very small amount). But you will also have to watch out for belt profile as you may cause excessive wear if the pulley profile doesnt match the belts'. 

Yes I agree with the increased speed raises the risks up if I were to hit something. However, I feel today's new craftmans gt mowers with thinner decks spin faster than our stock deck do and they are a thinner gauge for sure.. So I'm willing to take the risk..

 

The electric PTO idea I never played with those so I have no clue. I'm guessing it isn't rocket science..

I may have just the thing you want, if increasing tip speed is your goal. This is a double-pulley for the center spindle and it is only about 3" diameter on the TOP and BOTTOM of it. Usually, the top section is 4" or so, and the lower V pulley is 3" (estimates). This pulley is the SAME on top and bottom. Here is a pic...

For more info, send an email to me here:

daveoman@windstream.net

I will go measure my pulley today. As this may be an option for me to take as well.

[daveoman1966 3,586]

I will also measure that top & bottom dia of the double-pulley I have....  I know it is the SAME on top and botrtom.  

Please contact me by DIRECT email at this address:

daveoman@windstream.net

 

Edited April 11, 2015 by daveoman1966

[boovuc 1,090]

Sgt!

 

The newer Sears tractors you mention do mow at a higher speed but they also go through pulleys, bearings, belts and just about everything else all the time. Cheap Cheap Cheap! They are unsafe at those blade speeds and nobody is going to convince me otherwise. I often wonder how many people are injured each year by these decks throwing blades, other objects or their own shrapnel that goes unreported until someone looks into it after 20 years. Those stamped decks are thin so think about a 4 year old Sears deck that sits outside that is getting thin before the transmission and engine crap out. Especially with the common sense most people have and it adds up to the next big consumer safety concern.

[gwest_ca-(File Mod) 10,478]

It may sound like a higher blade tip speed but may be just more air noise due to turbulence. All manufacturers are bound by the regulated 19,200 feet per minute blade tip speed. Not hard to calculate if you know all the pulley diameters and blade length. Bearings also have a maximum speed.

 

Garry

[MalMac 1,328]

Wheel Horse came out with a pretty good product. A few engineers including are own Mr. Pond spent a lot of time punching numbers around to come up with a design that work to it's max at the same time being safe and efficient. Being my family was a old Wheel Horse dealer, I can tell you, you would be better served by leaving well enough alone. I have seen the effects of changing things on decks with well intensions. In the end result was damage, total destruction and the worst, someone got hurt.

[squonk 38,844]

I bought a 312 last year. The guy selling it had the belt on the outer PTO pulley. He also had the the center deck pulley flipped. That deck sounded awful. I asked him why and it was so he could mow faster.I got it cheap by the way it sounded. I put it back the right way and it's as quiet as a new deck. The guy's elevator din't go all the way to the top floor. He sold the 312 so he could mow his 2 acres with a walk behind Ferris with no sulky! 

[sgtsampay 117]

I just measured my pulleys. The center pulley is 3.5 to outside of belt and the same both top and bottom. Then if I'm still correct the big pulley on pto is 4.5 on the outside. 14 in center blade and the equation. States it's spinning at 16,900ish rpm. Kinda fast for that age right?

[tbarnhart 240]

It would seem fast enough. The best thing you can do for cut quality now is to keep your blades sharp. I'm sure that blades last longer, cut better, and use much less HP when they are sharpened regularly. I often pull mine and sharpen lightly after a few hours of cutting. Get your deck adjusted as well. The front of the blades should be slightly lower than the rear. Put the tractor on a level surface and set the deck to cutting height and adjust with the trunnion bolt at the rear center of the deck until the front is cutting about a 1/8 in. lower.

[clem 28]

I built a two sized pulley for a 48" sd to increase blade speed and found it was sketchy at best. It seemed that the biggest benefit was the extra lift created under the deck really helped keep the grass stood up tall in order to get a lower cut. The problem with that is these decks already cut pretty low and adjusting it upward causes a loss of seal of the deck to the ground so you then lose the extra lift you had gained. Another problem was the smaller pulley did lose enough contact surface to allow the belt to slip, not to mention the extra violent gyro created by the extra speed. Also, keep in mind that just flipping a stock two sized pulley over may not be the answer because it may change the size of the center pulley compared to the two outer pulleys (at least on decks with three blades). Once you do that, the two outer blades are spinning a different speed than the center which makes for an ugly cut also. IMHO, adjust the deck properly, file the blades about every three uses, and enjoy the ride as long as possible. If you're going to mow large areas and time is a concern, better get a big zero turn.

[Bob77A 10]

Hi:

 

I am new today to this forum, but in the interest of safety I must respond.

 

The United States of America Standards Institute, sponsored by the Outdoor Power Equipment Institute recommends for safety the maximum blade tip speed of 19,000 Ft./Min.  Which means the tip travels 19,000 feet in 1 minute.   Which is going 3.6 miles in 1 minute or about 215 mph in a car. 

 

Blade tip speed is caculated by the blade length and the rpm of the spindle it is mounted to.  The spindle rpm for a 16" blade length/diameter would be 4,542 rpm to achieve 19,000 ft/min tip cutting speed. , The same spindle  with a 24" blade length/diameter would be 3,023 rpm to achieve the same 19,000 ft/min cutting speed.  The larger the blade length, the less spindle rpm needed to accomplish 19,000 ft/min. There are charts online that show what rpm is acceptable for different blade lengths (saves on doing the math).

 

Blades fatigue while spinning and after cutting for awhile begin to stress crack.  If you hit something hard, it accelerates the fatique.  You can figure out what force the blade hits the grass (I am not going to do the math here) and if all is working properly the blade see's the grass as a solid object. You then get a clean cut.   Speeding the blade tip speed up, can cause the grass to pull and tear especially after the blade dulls a bit>

 

The lift wings on the blade are designed to lift the lawn at a specified rpm.  Speeding up the blade actually causes the blade to lift less (I have seen this also with leaf blowers where people speed up the engine thinking it will blow more, it doesn't, it blows less).  The wings also wear out faster at higher speeds.   The biggest concern is that a blade will shatter and become a projectile at higher speeds.  I have seen blades go right through most mower decks when they explode.  I have repaired many decks after this happens.  I can only imagine a blade fragment flying across the lawn into something or worse someone.

 

If in doubt, contact the blade manufacturer for the correct blade tip speed they recommend for that blade.

 

I don't want to see anyone get hurt or worse...

 

My 2 cents worth.

 

Bob H

 

C-160 Automatic   A hard working horse

[daveoman1966 3,586]

The double pulley I have is 3 3/8" dia on top AND bottom V grooves. The center shaft if 5/8" diameter.

Here are a cupld pics...

Me thinks the original top pulley is 4 1/4" dia and the lower one is 4" dia...not sure. In any case, this smaller 3 3/8" pulley here will definitely increase the tip speed.

[boovuc 1,090]

Thanks for chiming in, Bob and welcome to RedSquare.

Garry: Maybe it is the shear noise I hear from the craftsman and MTD machines that make me think they are spinning way to fast. I won't argue the fact that a lot of Craftsman and some MTD machines give a beautiful cut to a lawn. I just see too many of these lawn mowers eat belts and bearings at an incredible rate. I had a friend at work ask me how often I have to replace the drive belts, pulley belt and implement belts on all my tractors. I told him I have replaced two belts, both main drive belts, on two different tractors since the early 90's. (Need a pulley belt this year on the 310-8 Magnum).

He has to replace a belt a year on his Craftsman. This year, he needs two belts. Probably heat and I'm sure he has a bad bearing.

 

Bob: I didn't know there was an ASI Standard on blade tip speed though in our liability world, I don't know why i wouldn't have thought there wasn't. 

 

Very interesting post. 

[tbarnhart 240]

I appreciate all the safety related discussion in this thread. I sped up the blade speed on my 48 in. deck and have enjoyed a much better cut as a result, but I wouldn't recommend changing anything without a good reason and a good grasp of the process and the associated potential issues. I put my blade tip speed at approximately 17,500 fpm which is still well below the saftey maximum and spindle rpms shouldn't be too fast to wear anything out prematurely. Just randomly changing pulleys is asking for trouble. Boo, As far as the newer mowers eating belts, its largely an issue with the way the belts are routed on these newer vertical shaft tractors. Many of them use one belt going from the engine and around two tor three spindles as well as various idlers. Some even use this one belt as the clutch. Then remember that the angle of the pulleys varies quite a bit as the deck is raised or lowered. A lot of them simply don't run very straight. Manufacturers don't care, They'd love to sell you a $45 belt every year. As far as bearings, all the bearings in those spindles are sealed ball bearings that come from China. If you take a new spindle assembly for a Craftsman, Husqvarna, MTD, Troy-built, etc. and pop out the seal from those bearings, you'll find very little grease. Those things are dry from the factory and seldom last 200 hrs.