Mowing why does a rotary mower have only 2 cutting edges?

[KMA]

I believe the curved up back edge causes an area of lower pressure like a vacuum that pulls the grass upwards, allowing the mower to cut more evenly and completely. Blade speed is important for a quality cut, so more blades might actually do a worse job with the same HP due to weight, drag, etc. Plus, there needs to be some room under the deck for cut grasses to blow around and clear out of the blade's path. More blades would take up more space and could negatively affect performance. IMO the mower/deck would need to be designed for 4 blades in order for it to be effective.

 

[woodlandfarms]

Carl, Thanks.

My new observation on the four holes verses 2. If you wear or strip out the current hole the blades are mounted in, just switch the blades to the other set of holes.

I see you found that fence you were looking for.

Correct.. It is what Terry told me the additional holes are for. The belt drivin spindles (left and right) have hardened bolts and washers as bumpers. The center spindle now has no bolt bumpers, but just hex plugs to plug the holes...

 

[woodlandfarms]

Ultimately my mower is a rough cut mower / poor mans brush hog. It does both jobs adequately for our farm, but does neither very well...

If I had the cash, we would completely rethink the process...

 

[ponytug]

Dear Carl,

Drag is a big deal, and goes up with the square of the velocity, so 40% faster is twice the drag. As MR points out, there is also the issue of the flying particles of whatever is being mowed, which add further to the drag.

If you are getting more vibration, you might want to check the weights of your blades and especially the lengths from the center of the bolt holes to the ends of the cutting blades. Slight differences make a big difference in force on the spindle. (It is another mass times velocity squared thing; so small differences in length add up both in terms of mass shift, and in changes in velocity.)

Since the vibration represents uneven force on the bearings, you might want to track down the source of the variation, and I wouldn't over look the possibility that the bolt holes might not be exactly centered either.

All the best,

Peter

I never thought of aerodynamic drag. Or actually getting that sort of mass rotating.

I upgraded my PT blades from soft 3/8" to hardened 1/2" blades custom made, and it does take the PT more time to wind up that big mower... Also Vibrations are more prevelant...

JJ, Here is a couple of pix of the belly of the beast.

 

[woodlandfarms]

At speed the mower is smooth like butter. It is starting up that it has personality, very much like a real brush hog. I never noticed it with the ligher weight blades, but those blades were so poorly made.

 

[ponytug]

Dear Carl,

That's great! Speed is where it really matters, since that is where the forces are the highest.

All the best,

Peter

At speed the mower is smooth like butter. It is starting up that it has personality, very much like a real brush hog. I never noticed it with the ligher weight blades, but those blades were so poorly made.

 

[cqaigy2]

I never thought of aerodynamic drag. Or actually getting that sort of mass rotating.

I think that would be grassodynamic.

 

[MossRoad]

At speed the mower is smooth like butter. It is starting up that it has personality, very much like a real brush hog. I never noticed it with the ligher weight blades, but those blades were so poorly made.

Do you engage the deck with the engine at idle or just enough RPM to get it going without stalling the engine? Then, after it shakes and shimmies and comes up to rotation, increase the engine RPM to max.

 

[woodlandfarms]

I engage at low RPM's and then throttle up. The engine doesn't even wince swinging the weight.

I have never really bogged the engine mowin, I guess a bit, but the 65HP pushes the juice pretty well...

 

[J_J]

You all should know that at start up, the blades are probably never in the balanced state, and then centrifugal force takes over and extends the blades to the full cutting diameter.