Mowing 48" Finish Mower Questions

[SnowRidge]

48\" Finish Mower Questions

Rob, I'm curious as to why you went with the 48" mower instead of the 60" mower. The 60" seems like a better bang for the buck. We went with the 48" because of clearance issues with out Xmas trees. Did you have similar problems?

On a related note, has anyone noticed that the mower can strike the tilt ram when it is raised up high, unless you are careful to tilt it back first? It seems like some sort of raised bumper mounted on the mower deck might be in order.

The plastic gauge wheels have to go. Anyone got a rubber replacement source?

Last question -- any source for blades, other than PT?

Thanks,

SnowRidge

 

[Bob999]

Re: 48\" Finish Mower Questions

I have the 72" finish deck and have the same experience with the deck hitting the cylinder rod, and on my machine, with 72" lift, it is not possible to lift the mower to maximum height without hitting the rod--no matter what is done with tilt.

On mower blades--I found PT to be a very reasonable a convenient source. the 3 blades for my deck were $12.15 each plus shipping from PT. This price was comparable or better than alternative sources I could find.

 

[smartguyz]

Re: 48\" Finish Mower Questions

Hi SnowRidge,

I feel like I know you already!

To answer your question, I do have a 2+ acre property, with 2/3 of it landscaped. Of this, about 9000+ SF is fine grass. This is a relatively small amount of lawn, especially compared to guys whose entire property is 90 percent lawn area. My property has a lot of trees, flower and garden beds, etc. I went with the 48" because my JD 318 has a 50" mower, and it works very well in mowing - I consider the 50" an excellent size for this lawn - and the 48" was really close in size. I suppose I should have gone for the extra 12", but I haven't missed it yet. It probably takes a few more minutes to mow my lawn, but the 48" is lighter (I don't know by how much, does anyone know?), was simple to transport in a standard pickup truck, was cheaper, and smaller mower decks usually have a higher rotor speed and achieve a higher blade tip-speed for a finer cut.

For example, one set of mower decks I was looking at had both 48" and 60" variants.

For the 48" deck: rotor speed is 1,042 rpm, 12,560 ft. per minute blade tip speed

For the 60" deck: rotor speed is 794 rpm, 11,948 ft. per minute blade tip speed

Although these are not the PT specs, I would think things would be comparable. The 60" deck is normally a lot heavier, and it usually has a lower blade tip speed. Not a big deal, but choosing the smaller mower deck made it easier to move, easier to store, and easier to justify the purchase of the mini-hoe!!! /forums/images/graemlins/grin.gif

Thanks for asking. How are you enjoying your PT?

Last night I moved the last of the bark mulch (snaking through tight turns, up steep grades, and along grassy spots and through garden beds (with NO damage!!!), and swept the entire courtyard, and the long driveway, and the common-access roadway along the front of the property - took me about 3 hours, and it would have taken me the whole day to do this with any other machine, plus lots of skinned knuckles. Switching implements is SO easy! Love it!

This is one useful tool!

 

[SnowRidge]

Re: 48\" Finish Mower Questions

</font><font color="blue" class="small">( Although these are not the PT specs, I would think things would be comparable. The 60" deck is normally a lot heavier, and it usually has a lower blade tip speed. Not a big deal, but choosing the smaller mower deck made it easier to move, easier to store, and easier to justify the purchase of the mini-hoe!!!
Thanks for asking. How are you enjoying your PT? )</font>

Hey, that makes a lot of sense--especially the bit about the mini-hoe. /forums/images/graemlins/smile.gif

We're having fun with ours. We've got 12 hours on it so far, and except for the few rough edges I've posted about, we are really happy. Best of all, we haven't set it on fire again. /forums/images/graemlins/grin.gif

SnowRidge

 

[Schultz]

Re: 48\" Finish Mower Questions

Someone calculated the blade tip speed in another post to be around 17,000 ft/min on the 60" deck. Which is right up there with the commercial mowers. Sorry, I couldn't find the post.

I'm not sure anyone has calculated this for the 48", but I would suspect the blade tip speed to be slower for the 48" since the three blades are about 4" shorter. Just for them to travel at the same speed would require the spindle speed to be 23% faster or 3821 rpm. Dose PT use different hydraulic motors for the two different decks?

My calculations using your rotor speeds only provides tip speeds of

4635 ft/min on a 48" using a 17" blade & 1042 rotor rpm
4346 ft/min on a 60" using a 21"blade & 794 rotor rpm

The formula I used is: (Blade diameter in feet)(3.14)(blade rotor rpm) = blade tip speed in feet/min

 

[smartguyz]

Re: 48\" Finish Mower Questions

Interesting, Shultz -

However, I don't think there is a 1:1 correspondence with RPM of the rotor and how fast the blades spin, as there is also a belt and a series of pulleys on each deck. We need to take into account the ratios of the pulleys and determine the actual spinning speed of the blades.

Therefore, there are more variables, and I don't think your calculations will be valid. We need to know:

Rotor Speed
Diameter of Rotor-Driven pulley
Diameter of belt-driven pulley
Length of blades

Anyone care to chime in?

Sincerely,

Rob /forums/images/graemlins/grin.gif

 

[F350Lawman]

Re: 48\" Finish Mower Questions

I think the calculations are going to be pretty close. If you pick up any brochure for mowers and look at the listed tip speeds for the blades of diff. sized mowers they seem to decrease in accordance with the size of the mower. At least in the brochures I have.

 

[SnowRidge]

Re: 48\" Finish Mower Questions

</font><font color="blue" class="small">( Dose PT use different hydraulic motors for the two different decks? )</font>

Don't know--yet. Our 48" has a MGG20020 BB1A3 motor. Anyone with a 60" care to take a look and post what you find?

SnowRidge

 

[Schultz]

Re: 48\" Finish Mower Questions

Is the hydraulic motor coupled directly to the middle blade spindle?

 

[SnowRidge]

Re: 48\" Finish Mower Questions

</font><font color="blue" class="small">( Is the hydraulic motor coupled directly to the middle blade spindle? )</font>

As far as I can tell without taking the top cover off, it is. The spindle is directly below the motor.

SnowRidge

 

[Schultz]

Re: 48\" Finish Mower Questions

That makes it easier, and the above formula will work. I did some digging since I have an interest in owning a PT some time next year.

Using the numbers you gave me the motor is a Gresen high-speed geroter motor. .45 in3/revolution
8 gal = 1848 in3 - from PT's 8 gpm pto
1848/.45 = 4106 rpm

Gresen motor

PT's 8 gpm max pto output provides 4106 rpm at the motor shaft, which is also the blade spindle.

With a 17" blade diameter, I guessing at the blade diameter, but please post the actual diameter.

This provides a very respectable blade tip speed of:
17/12*4106*3.14 = 18,264 ft/min

Now this calculation doesn&#8217;t account for the volumetric efficiency of the motor. If the motor is only 90% efficient then the blade tip speed drops to 16,438 ft/min.

 

[SnowRidge]

Re: 48\" Finish Mower Questions

<font color="green">( Gresen motor

PT's 8 gpm max pto output provides 4106 rpm at the motor shaft, which is also the blade spindle.
With a 17" blade diameter, I guessing at the blade diameter, but please post the actual diameter. )</font>

I found that page too. The listed motor is not identical to the one PT uses. The mount is different, I think (BB1A3 vs. BA1A3).

Interestingly, the motor says Parker on it, not Gresen. However, I couldn't find that part number in the Parker catalog. Did Parker buy Gresen?

The blade diameter is 16 1/2 inches, measured cutting tip to cutting tip. The blade is not quite rectangular.

SnowRidge

 

[smartguyz]

Re: 48\" Finish Mower Questions

Hi Schultz,

Pretty decent tip speed!

I note from your profile that you have an ingersol tractor with a hydro-vac attachment. Do you think that this can be adapted to make the PT 48" finish mower deck into a convertible bagger system? I just finished sending away for an ingersol catalog and speaking to their salesperson, I am of the opinion that this might be doable. Since you own one, what's your take on this?

I spoke to Kristie a couple of weeks ago, and suggested that a bagger assembly for their decks might be a popular item. She just said she'd take a note on the suggestion. I'd like one just for the yearly bagging of the output of all my trees, which drop just a huge load of leaves around the property every year. Having the PT do duty here would be wonderful.

Anyone have thoughts along these lines?

-Rob /forums/images/graemlins/grin.gif

 

[MossRoad]

Re: 48\" Finish Mower Questions

Hey, Rob... nice picture in your signature! /forums/images/graemlins/smile.gif

I think a leaf pickup system would be awsome for landscapers and folks with lots of trees. My guess is it would be pretty expensive, but worth it to some.

 

[Schultz]

Re: 48\" Finish Mower Questions

<font color="blue"> </font>

Indeed, even with a 16.5" blade the tip speed is in the neighborhood of 17,700 ft/min.

Like you, I have the yearly dump of oak & maple leaves. This was one of the main reasons I bought the vacuum. I don't think I could justify the new price of somewhere in the $1200 range. I was patient and asked a couple of the dealers to call me when one became available. I paid $350 used, it was used very little since the paddle wheel and inside housing still had much of its paint on it. I also use this to pick up grass clippings in the summer that I add as mulch around tomatoes and other plants. After that, it's removed and sits in the corner until fall.
Unfortunately the Ingersol vacuum isn't designed for the 60" deck, I had to modify it to work with mine. When the grass is heavy, I have to go slower or take less of bite. The 6" hoses will plug with grass or debris at the mower deck hose bend. Since my use is limited, I haven't spent much time on it to solve the problem. I think if I used 8" hoses and adapted it down & up at the vacuum housing, the hose probably wouldn't plug. To answer your question: Now that I know its limitations, it never or rarely plugs for me and I really like it for leaf and heavy grass pick up. My wife doesn't care for it because it plugs a lot for her, and I don't think she has used it in couple of years. She does 95% of the mowing.

I plan to keep the lawn vac and use it on a future PT. One of the other guys has made lawn vac to fit his 60" deck, but uses an engine driven vacuum. With the Ingersol unit you may need to change the hydraulic motor to speed it up, the Ingersol unit works on 9.5 gpm, so PT's 8gpm may be too slow? But in concept it would be placed in series to the mower. Some other posts, I saw a link to Walker mowers, they too have a rear discharge collection system and maybe some parts could be scavenged off their machines?
We need to hound the guy that has the vac system on his PT to post some pictures.

 

[SnowRidge]

Re: 48\" Finish Mower Questions

<font color="green">( ( Dose PT use different hydraulic motors for the two different decks? )

Don't know--yet. Our 48" has a MGG20020 BB1A3 motor. Anyone with a 60" care to take a look and post what you find? )</font>

Found this 60" motor reference in another thread: Gresen MGG20025BB

SnowRidge

 

[Schultz]

Re: 48\" Finish Mower Questions

Thanks for the part number.

Just for completness, I'll put the 60" calculation here so it's all in one thread and I'll use a 20.5" blade. If anyone has the exact size, they can chime in.

The MGG20020 BB1A3 motor is a .58in3/rev motor

1848 in3 = 8 gpm
1848/.58 = 3186 rpm

3.14*20.5/12*3186 = 17,090 ft/min tip speed.

Yep, Smartguyz was right, the 48" is 4% faster at 17,700 ft/min, but they are very close. I guess it's the engineer in me that has to see & do the calculations before I'm satisfied.
Tim