Ping Soundguy RE: Woods BB72

[have_blue]

Soundguy,

You asked how my 35HP tractor pulled my BB72. I finally mowed my field with 6-8" grass and chest-high weeds. Well, it did fine. I used 7th gear, which is a pretty good clip. I ran at 2000 RPM, which is well below 540 PTO RPM. I was pleasntly surprised at how effortlessly it cut. Instead of a grinding, flailing sound, it made a quiet snipping sound. I could have easily gone to 8th gear and 540 PTO RPM, but my bones wouldn't take the pounding from my rough field. I plan to keep running at 2000 RPM, because I want to keep my blade tip speed down. Every few additional RPM's makes the blade dull out ever faster. If it ever quits cutting smooth, I'll stop and sharpen. Instead of doing a few major sharpening jobs, I'll do a quick touch-up every time I mow.

 

[Soundguy]

Thanks for the info.

I may have to get a 72 myself... If I can ever get all my other projects off my back.. that and beg the 'treasurer'.

Soundguy

 

[have_blue]

</font><font color="blue" class="small">( Thanks for the info.

I may have to get a 72 myself... If I can ever get all my other projects off my back.. that and beg the 'treasurer'.

Soundguy )</font>

Hahaha... I see you use the same terminology as me. When it has to do with inside the house, she's the "Secretary of the Interior". When I need to spend big money, the Secretary of the Treasury". When she's mad, she's the "Secretary of War".

 

[MDSteve]

I also run a BB72 with my L3710. Works great but I don't want my blade to be sharp when I use it for brush work. When I first got it taking down sapplings and small trees left sharp sticks and stumps. Now that the blade is blunt it just shatters the trees and they seem to rot better and not grow anymore. I use a finish mower to go over the pasture if the horses can't keep up with it. But I don't let it get waist high.

Steve

 

[theboman]

The higher RPMs the easier on the tractor. You can't over rev a tractor engine, they are designed for this purpose.
The higher the RPM on the PTO the more effective the device works.

I'm guessing the BB72 is a rotarty cutter, those blades are not exactly sharp, its a cutting edge and brute force doing the damage. I'd rather break a $50 blade than a $20,000 tractor.
Then again if the BB72 is a mower the higher the RPM the greater the lift of the grass for a smoother cut.

Implement makers tell you minmum RPMs, they use those numbers for a reason that includes warranty, safety and effectiveness.

 

[have_blue]

</font><font color="blue" class="small">( Implement makers tell you minmum RPMs, they use those numbers for a reason that includes warranty, safety and effectiveness. )</font>

Hey Bo,

You're right of course, but I'm taking all that into consideration. The manufacturers certainly give you an operating range based on all conditions, and shaded toward the worst conditions I bet. Rather than blindly follow the factory specs, I look at the purpose behind the specs.

My conditions are far from the worst. In fact, I let my weeds go an extra week this time just to try out my new brush hog on the worst conditions I should see. I only have short grass and tender weeds, and I'm hopeful this was the worst conditions I will see this year.

Strain on the tractor and strain on the brush hog are 1 in the same. I use a sharp blade to cut the grass rather than relying on high tip velocity to explode it. I can get away with this because I sacrificed my previous 60" brush hog to cut all the brush and stumps in my field. I now use the lowest RPM I can while cutting smoothly and without any abuse to my tractor. If my tractor's RPM should drop even 100 RPM, I would run in a lower gear or sharpen the blades.

Yes, if you try to bruise the grass into submission, you need to apply horsepower! Cutting brush also requires maximum RPM.

While cutting, the last 100 or so of PTO RPM probably absorb more than half of the PTO horsepower used. That last 100 RPM's may only do a lot of grinding and flinging weeds against the housing, which is mostly wasted power and fuel. A sharp blade at lower RPM is far easier on all the equimment. All bets are off if the engine starts lugging. /forums/images/graemlins/wink.gif

Bottom line, a cutter blade should be run at the lowest RPM at which it cuts cleanly and without lugging. When you see shredded balls of grass and weed stems, you're only wasting fuel and dulling your blade to create noise.