Grading Finish Blade test - the blades

[Charlie_Iliff]

Re: Finish Blade test - qualified success

Can't quarrel with the math. Empirically, however, the correllation between overheating and finding dust caked on the oil cooler is still 100%. With four blades per spindle, either factory or mine, I mow in a cloud, requiring a dust mask. Raising the deck helps, taking half the high lift blades off helps more. When I encountered heavy growth with the four blade setup, both factory and mine, I could not hear significantly more rpm drop than with the 2 blade system. Going uphill drops it more. Some day maybe I'll cobble up a spindle tach. That might be of interest anyway, but if I am getting pretty good results and not overheating, I'll probably lose interest.

 

[Charlie_Iliff]

Re: Finish Blade test

John: I change mine with an air impact wrench, and often with an eager helper. Without the wrench, I'd never remove the blades at all. (Incidentally, when you've mowed a number of rocks, the heads of the mounting bolts start to assume different shapes. I discarded a few and replaced them with grade 8 bolts, which may last slightly longer, but all will wear. I don't even want to think about not being able to get a socket wrench to hold on the bolt heads.)
I think your observation about the rear rubber skirt may be exactly right. If you do take it off, I will be very interested to hear how it goes. I'll try to remember this weekend to look under mine to see how close the blades are to the back. Maybe a chain guard?
Yours sounds as if it is actually running hotter than mine. I haven't a clue how accurate the gauges are. Only once did mine act strangely when overheated. The last time, the needle was just about exactly on the 240. When I turned off the mower and reduced rpm, I heard the "alarm", which I had previously only associated with ignition and seat switch on, but no oil pressure. I think we need a panel strobe light, rather than an audible alarm. I'm so attuned to watching the gauge, however, that it will be well down my to do list.
This morning, I measured the slope of one of the hills I have mowed. At its steepest, it is about 30 degrees. I am able to poke the mower up into that part, but lose traction and can't keep driving up. I actually lose grip and slide sideways on slopes as little as 20 degrees when driving on fresh mowed grass. I can climb them easily straight up when dry. I looked around the place and didn't find any that I can say was as much as 27 degrees that I have climbed. With the turfs, I always lose traction before bogging the engine or stalling the wheel motors.
E-mail me your mailing address and I will send you six of my modified blades for testing. Since I had one apparently successful test, I'll want them back, but I'd like a second opinion. They are only 1/4 thick, so a little sloppy on the rough-cut bushings. If you are successful at cutting your own, you may be able to reduce the distance between the stump jumper and washer so they don't move as much. I doubt that will affect the cut, but may reduce wear.
One advantage of the modified blades is their offset downward about an inch. The deck can therefore be set higher for the same cut height.
Incidentally, last night after the pasture, I mulched some Kudzu along the road, and, of course, scalped some dirt. I haven't inspected the blades closely, but they continued to mow. The factory finish set would not have survived.

 

[duane]

Re: Finish Blade test

Charlie,

Great test and a great job posting. Couple of comments:

1) With the efficiency of the hydraulic PTO pump (80% at best) and attachment hydraulic motor (80% at best), each 1 horsepower increase at the rough mower shaft translates to a 1.56 Horsepower increase seen by the engine. You can quickly eat up any reserve engine power.
2) I thought of adding finish mower blades to my PT422 brush cutter, but when I calculated my blade tip speed, it would only have been 9,600 fpm. My Toro Wheelhouse and most other mower blade tip speeds are in the range of 16,000 fpm. I am not sure how blade tip speed translates to the lawn cut appearance.

Duane

 

[Charlie_Iliff]

Re: Finish Blade test

Duane:
My understanding is that the primary reason for high tip speeds is the ability to run the machine faster over the ground. Some ZTRs are apparently mowing at 12 or 13 mph. I assume that is on very smooth stuff, or we'd hear about a lot of operators being bucked off.
From occasional research on lawnsite, and talking to people like Hans (Bubenberg) I have the impression that the primary variable in cut appearance is blade sharpness. That assumes, however, that the deck is designed for the amount of lift that the blades are developing. There is a lot of debate about double blades, high lift v. medium, etc., but I've not seen much real information about shape and placement of baffles and actual air flow under the decks.
I don't have any clue about my blade tip speed. I may do a little work to find out. Mowing uphill, I drag the engine down, much more than the mower slows when hitting really heavy growth, so I don't think I am short of power at the mower. It is a 72" three-spindle rough cut deck with stump jumpers. I have run a shaft driven 72" single spindle brush hog for years on approx 30 hp JD 950, and a 72" three spindle Jacobsen Turf Cat side discharge hydraulic finish mower with a 21 hp Kubota Diesel. Even with some inefficiency, and pretty aggressive blades, with the 45 hp Deutz, I shouldn't be running out of horsepower.
As an aside, if Sedgewood and I figure a way to get more air flow out from under the deck, I am pretty sure we will get better cut quality. The horsepower draw will probably increase, however, rather than decrease. The drag of a propeller actually able to pump - to establish air flow - is greater than one spinning in a stagnant pool, where the air can't get out. (I learned that when we gained a few horsepower by locking Corvair heating boxes shut, thus reducing flow over the engine. The cooling fan drag was greatly reduced - as was the cooling, of course.)

 

[MossRoad]

Re: Finish Blade test

<font color=blue>The drag of a propeller actually able to pump - to establish air flow - is greater than one spinning in a stagnant pool, where the air can't get out. </font color=blue>

That's probably true. Ever plug the end of your shop vac? You'd think the motor would bog down but it actually increases in speed because there is no more air flow and the motor has less drag.

 

[Sedgewood]

Re: Finish Blade test

Charlie:

Oh my gawd the pain of internet withdrawal is severe! My ISP disappeared late last week and never came back. Just, well, GONE! So I apologize for the delayed response.

<font color=red>I think your observation about the rear rubber skirt may be exactly right. If you do take it off, I will be very interested to hear how it goes. I'll try to remember this weekend to look under mine to see how close the blades are to the back. Maybe a chain guard?</font color=red>

First off, I tried the 12 blade setup and found heating to be much more severe with no real improvement in the cut. Then I went back to 6 blades and took the skirt off. Major improvement. Much less jambing and striping right of center. It does still have a hard time with tough patches of full grown goldenrod, as I recall my Bush Hog doesn't handle all that well either. On normal mature hay & weeds a half overlap double cut leaves very few survivors, less so than the Bush Hog. On 8-10 inch grass I can now cut it to 4 inches basically at full tilt with very little jambing & striping. The grass discharges as full length stalks and is not pulverized like it was with the skirt on, which is fine with me, I ain't buildin' a pianer.

As far as the safety of removing the skirt is concerned, first let me say here that I'm not recommending anybody remove their skirt tee hee but I feel ok with mine off IF I KEEP THE DECK ON THE GROUND. The steel deck edge has a downward slant so stuff doesn't seem to fly around though the bottom 3-4 inches of the tractor frame does get plastered with grass goo. To attack Multiflora Rose etc I'll put the skirt back on. Its just a three bolt deal.

<font color=red>Yours sounds as if it is actually running hotter than mine. I haven't a clue how accurate the gauges are. Only once did mine act strangely when overheated. The last time, the needle was just about exactly on the 240. When I turned off the mower and reduced rpm, I heard the "alarm", which I had previously only associated with ignition and seat switch on, but no oil pressure.</font color=red>

I think we're about the same. I get a continuous alarm when mowing at anything over 80 degrees or so but the needle never goes more than a needles width over 240. I've had no erratic running so far, even at 95 degree ambient.

<font color=red>I think we need a panel strobe light, rather than an audible alarm]</font color=red>

I think we need a cooling system. Unless by chance the temp gage & alarm are being way too conservative. And they may not be if you got some erratic running.

 

[GlennT]

I wonder if another factor is at play here. A shredder has to be adjusted so that the front is about an inch lower than the rear; if this isn't done the blade in essence cuts the same material twice and increases the load on the shredder and the tractor considerably. I wonder if increasing the number of blades as you have done keeps the material at and above blade level too long and increases the load on everything. This would be great in a mulching mower but maybe not so good in a shredder.

 

[Charlie_Iliff]

Glenn:
I think you're right. The last field I did was with the front of the deck lowered. This weekend, I'll try to make time to put it on a concrete floor and get an idea how the wheel settings relate to deck and blade angles. I haven't really paid attention to that. I raised the deck to its highest levels because my experimental blades were offset downward, cut with four per spindle, then two, and then canted the deck with the two. That last setting seemed dramatically better, but I've only done one field of fairly heavy ungrazed grass and weeds.

 

[Charlie_Iliff]

Re: Finish Blade test

John:
As noted earlier, my most dramatic improvement has been with the offset sharp blades, with the front of the deck an inch down at the wheels. It still pulverizes pretty well, but with little or no uncut stripe. I was barely overlapping, so getting about 5 feet of new cut per pass. I have only tried it on 8-12 inch ungrazed pasture; no really tall or thick stuff. The engine slowed a bit on the thickest stuff, but held rpm OK if I reduced speed a bit. I did wade into 2-3 foot kudzu, however, and it disappeared nearly completely. Very satisfying.
I'll be doing a little more experimenting this weekend, but hope also to make a little progress on the string trimmer project, which stalled due to mowing, sick horses and hot weather.
Let me know if you want to try six of the offset blades. At some point I'd like to get in position to make some suggestions to Power Trac, but need additional understanding of what happens with different setups in varying conditions.
I listened more carefully, and occasionally turned off the mower the last field I did. The temperature never got to the 240 top line, and the alarm never went off. Ambient was in the 90 range. When I checked the bottom of the oil cooler, it had about 10% blockage after 1 1/2 hours, much better than with the additional blades.
After you got yours hot with the four rough-cut blades, did you blow out the cooler? I've started doing that as a routine after each mowing session. A cheapo tire inflator seems to work between trips to the big compressor.

 

[Sedgewood]

Re: Finish Blade test

Here's a before picture I took yesterday before mowing with 6 rather dull roughcut blades, rubber skirt off, deck set at 2nd from highest in rear and 1-1/2 inches down in front. On the left the grass is about 6 inches tall with some taller weeds. Stuff on the right is uncut this year, maybe 3 feet tall, thick grass with a goldenrod patch near the edge of the drive (doesn't show in picture)