Rotary Cutter Blade tip speed

[Brads 1715]

I've not found any of these smaller rotary cutters that have a 1:1 gear ratio.... :anyone:

 

[TomSeller]

The smaller you go on the mower width, the faster the mower blades need to turn compared to the PTO shaft to get back to the same tip speed. So yes, smaller mowers would have higher Blade RPM ratio to PTO RPM.

 

[LD1]

And clearly the OP is looking at two mowers with differing tip speeds. How do you suppose they get different speeds???

 

[JHTFarmer]

The rotor bearing on a 5 foot cutter will need to revolve about 200 more times per minute, a 25% increase in order to pick up tip speed from 13,000 to 16,000 fpm. So one may argue that with all things being equal, the slower rotor will last longer between major overhauls and failures.

Also, doubtful that most blades of grass being struck by a 25 pound cutter blade will appreciate any difference between being struck by one traveling at 180 mph vs one crawling along at a leisurely 160mph.


Yikes, then there's the mass of the blade to consider. Kinetic energy= 1/2(mass) x (velocity) x (velocity). So it's easier /cheaper for a manufacturer to get more energy to the blade tip by increasing its rotational speed than increasing its mass. But a heavier blade will be more durable than a light one.

So, just can't look at blade tip speed as its only one of several variables.

 

[LD1]

Its more like 148mph vs 182mph, but whos counting....

 

[Chilly807]

Another thing to look at is the weight of the cutter itself. Will the tractor be able to handle the larger cutter without wanting to pick the front wheels off the ground at every bump?
My Land Pride 1860 (5 foot) weighs almost 700 lbs, my L3400 will handle it with no problems, but I wouldn't want the same class cutter in a six foot model hanging on the 3 point arms going over rough ground.

I think my gearbox ratio is around 1:3, not an exact number though.

Sean

Sean

 

[Brads 1715]

I have a FEL on this tractor so i think the weight should be okay. I measured across the back of the tractor and the weith is 55 inches. I found a new woods rotary mower. Its and HC54 with a 54 inch cut. This looks like the one im going with. Has anyone used a woods HC54???

 

[SPYDERLK]

They are not all 1:1 gearboxes....

Im betting none on 5' cutters are 1:1. 6' would be ok for tip speed at 1:1 I guess ... but still, the refresh rate of a blade spinning only 540 would limit groundspeed a bit.
larry

 

[LD1]

My bushhog model 105 had a 1:1.5 box. So @ 540, it is spinning 810rpm. Its a 5 footer, so that's a blade speed of 12,700.

My model 306 is a 1:1. Its speed being 6 foot is only 10,200.

So yea, not many small cutters will be 1:1. If they were, they wouldn't cut for crap.

 

[the old grind]

I agree that tip speed could be a bit over-rated, nice with a finish mower's sharp blades on soft grass, but some of us will distinguish between a field and a lawn. Hogging brush relies quite a bit on flywheel effect of rotating blade mass, where sharper blades would indeed nick/gouge more easily. (How neatly must we manicure what we're cutting from stem to leaf?)

Forward speed, like pass width, determines how much uncut material goes under the blade tip per revolution. We adjust 'feeds & speeds' when machining metal to get the best match-up. Cutting is cutting, and cutting wider with less HP is but a matter of what gear/speed we choose to compensate for the width cut or tool diameter, to draw a ~ parallel. No absolutes here, just getting a feel for what works best. If you bog down, then gear down. Not rocket science, and no calculator or spreadsheet needed.

 

[SPYDERLK]

A 540 blade rpm youre going to run beyond the sharpened area at about 6mph. I often mow a little faster than that.
larry

 

[Hollow]

I agree that tip speed could be a bit over-rated, nice with a finish mower's sharp blades on soft grass, but some of us will distinguish between a field and a lawn. Hogging brush relies quite a bit on flywheel effect of rotating blade mass, where sharper blades would indeed nick/gouge more easily. (How neatly must we manicure what we're cutting from stem to leaf?)

Forward speed, like pass width, determines how much uncut material goes under the blade tip per revolution. We adjust 'feeds & speeds' when machining metal to get the best match-up. Cutting is cutting, and cutting wider with less HP is but a matter of what gear/speed we choose to compensate for the width cut or tool diameter, to draw a ~ parallel. No absolutes here, just getting a feel for what works best. If you bog down, then gear down. Not rocket science, and no calculator or spreadsheet needed.

Thumbsup

 

[JHTFarmer]

Just looked through the specs of the Bush Hog line of single spindle rotary cutters. Didn't see any correlation with increasing blade tip speed and cutting ability. In fact, appears inversely proportional:

SQ 172, 2 inch capacity, 14,963 fpm

Model 286, 2.5 inch capacity, 14,877 fpm

Model 296, 3 inch capacity, 15,268 fpm

Model 326, 3.5 inch capacity, 13,966 fpm

Model 406, 4 inch capacity, 10,179 fpm


Except for the model 296, blade tip speed generally decreases for this line of cutters as they go from light duty to super heavy duty... What does go up, though , is the mass of the cutting blade.

 

[TomSeller]

Like engines, there is nothing like displacement.

 

[Midniteoyl]

Just looked through the specs of the Bush Hog line of single spindle rotary cutters. Didn't see any correlation with increasing blade tip speed and cutting ability. In fact, appears inversely proportional:

SQ 172, 2 inch capacity, 14,963 fpm

Model 286, 2.5 inch capacity, 14,877 fpm

Model 296, 3 inch capacity, 15,268 fpm

Model 326, 3.5 inch capacity, 13,966 fpm

Model 406, 4 inch capacity, 10,179 fpm


Except for the model 296, blade tip speed generally decreases for this line of cutters as they go from light duty to super heavy duty... What does go up, though , is the mass of the cutting blade.

The more mass there is, the lower the speed needs to be..

 

[Hollow]

The more mass there is, the lower the speed needs to be..

Brown Tree Cutters turn at 15267fpm. Ya don't get much more mass than that! LoL

 

[Midniteoyl]

Brown Tree Cutters turn at 15267fpm. Ya don't get much more mass than that! LoL

ouch.. that'll leave a mark!