Rotary cutter blade speed

[savoy9020]

What is the rpm of (brand x) 3 pt, 540 rotary cutter blade speeds?

Is the gearbox a 2:1 or higher?

Have an old deck might want to repurpose the gearbox..

 

[Vigo]

From what i remember it is around 1.4:1, but i suspect there is a range. Easiest way to find out it just to look up ‘rotary cutter gearbox’and note the ratios.

 

[jimh406]

RPM is not directly related to tip speed since blades are different lengths. Generally speaking, faster blade tip speed is a cleaner cut. I guess I'd try it and find out how it does.

 

[Vigo]

A “good” blade tip speed for GRASS cutting is about 200mph, or 17,500 feet per minute.

You get a 5’ bush hog, 5 x 3.14 (pi) gets you ~16 ft circumference or 16ft travelled by a blade tip in one revolution.

17,500 / 16 = ~1100 revolutions per minute for the tips to travel 17,500 feet in that minute. 540 / 1100 = ~0.5. So you’d need a .5:1 overdrive on the gearbox to get 200mph tip speed on a 5’ cutter with a 540rpm input.

But bush hogs dont cut grass like finish mowers. Im pretty sure bush hogs have something more like the ~1.4:1 number i mentioned. But this gives you some idea of the math you could do to figure out a tip speed from your gearbox ratio and cutter diameter, or what kind of gearbox ratio youd need to make a certain tip speed with a certain cutter diameter etc.

 

[Flintknapper]

RPM is not directly related to tip speed since blades are different lengths.

Correct. Blade tip speed (because of varying blade lengths) is expressed in Feet Per Minute not Revolutions Per Minute.

We don't know the application the OP is considering for re-purposing a gear box, so its hard to provide anything useful....beyond what has already been submitted.

 

[SDT]

What is the rpm of (brand x) 3 pt, 540 rotary cutter blade speeds?

Is the gearbox a 2:1 or higher?

Have an old deck might want to repurpose the gearbox..

Varries by model number mower size, etc.

That said, the ratio of the replacement gearbox on my Frontier RCR 2060 (5') is 1:1.47, which is just a bit lower spindle RPM than is the ratio of the OEM gearbox. No noticeable difference in performance.

Different size cutters within same series have different ratios because radii of blade tips vary.