Why 540 RPM?

Very interesting. That almost sounds like the stories why train tracks are 4' 8 1/2". Or how the width of a horses butt or the chariot wheel spacing determined the size of the space shuttle boosters. Other crazy stuff like we have 60hz and most of the world is 50hz. How to figure that 60psi. Is a good house water pressure. Makes your head spin. Fun night time story. Good night.
 
As it was explained to me in college the sickle in a mower or any other cutterbar works ideally at about 1200 strokes per minute. 2 strokes per revolution gets you to 600 rpm. Any more and you are just wasting energy and beating the machinery to death with no gain.

As to why 540 instead of 600 is quite another question.

On a side note the same "ideal" speed applies to augers also. Overspeeding a auger only wears it out quicker with no real gain in capacity. Look around and find 1000 rpm drive auger!!

jt
 
If you divide the engine speed by 4 that will work out to about 540, and if you take the older slower speed tractor engines, and divide them by 3 you also get close to the 540 PTO speed. Another words 540 x4 is 2160 about what engines run today the same for the older engines 540x3 is 1620 or approximately what those ran back then.
Though the premise of the 5-600 RPM's for equipment would also make a plausible method for this during testing. I don't doubt either way would have worked for the determination.
 
No clue why 540.
Tach on Jubilee shows 540 at 1550 RPM.
I mow at 1800 rpms, engine can run faster. Woods finish mower is set up for 540. The blades sing in the wind at 1800 rpms. Grass lands about 12 ft from mower.
My farmall C can only do 1550 rpms no more, 540 pto.
 
I liked the part in Andy's clip about herding a bunch of cats. Never did it but understand the limitations.

On the sickle bar rate of speed, that makes sense. On the 3 vs 4:1 gearboxes that too makes sense. On standardizing things that makes sense.

On the PTO shaft diameter, as I recall my first TO 20 had a 1 ⅛" shaft, or it was my first tractor a Farmall Super A, and I had to have a 1 ⅛ to 1 ⅜" adapter along with an overrun clutch (a second adapter) to run my first shredder a well worn out 5' piece of junk but I could afford it and it worked....somewhat.....talk about shaft singing to you...wobble wobble wobble.
 
Yep, the sickle mower explanation makes the most sense. Back in the 1920's ag engineers probably did not envision tractor power driven forage harvesters or balers to name a couple of machines. The power mower was the dominant PTO driven machine in the industry and things went from there. Low torque machines that soon followed such as the manure spreader and corn picker did not care as to tractor shaft speed. When high torque machines such as balers and forage harvesters came along then the engineers sensed the need of a higher out put tractor shaft hence 1000 RPM PTO. I've run a 540 RPM NH 782 forage harvester and an 1000 RPM NH 790 forage harvester and the 790 runs considerably easier.
 
An old-timer shared this when I asked the same question as a kid in the 1950's:

First factory-installed PTO was on the IHC 8-16 in 1918. At governed engine speed the transmission countershaft on the 8-16 spun at 540 RPM. And since the rear of the countershaft is a logical (and easy) point from which to obtain power for a PTO, 540 RPM became the "standard" PTO speed. Also since the 8-16 countershaft spun clockwise as viewed from the rear of the tractor, CW became the standard direction of PTO rotation.

Don't know if this is true. But it does make some sense.
 
The size and speed wasn't standardized yet when AC came out with the All Crop combine. Walt Buescher talked about it in his book Plow Peddler. They had to make adapters for different makes. It's been so long since I read the book that I don't remember anymore if he said why they settled on 540 or not.
 

1800rpm pto would have made sense to drive a generator. Would also made for a direct pto drive without gearing possible .
 
I've forgotten the formula for converting fractional RPMs to metric RPMs, but I think it has something to do with the thumb size of the Queen of England - when she dies, we are all going to be in a fix!
 
standard speed for a circular sawmill's headsaw is 600 rpm. Guess the machinery at that time operated best at those ranges (550-600 rpm).
 
The IHC 10-20 was one of the first tractors to have a PTO as a standard attachment. It was running at 540 rpm. The coupling was a 1 inch left-hand thread. The Farmall PTO ran a bit slower but used a 1-1/8 inch 6 spline shaft. The later F-20 followed suit. The F-30 had a 1-3/8 inch 6 spline shaft. The F-12 used 540 rpm and 1-1/8 6 spline shaft. Other brands of tractors were slower to provide a PTO and all sorts of speeds and couplings were in use. When the 1938 standard was introduced the IHC 540 =/- 10% became the standard (first in wins) and 1-1/8 inch for lower powered tractors and 1-3/8 inch shafts for the bigger tractors was the standard. Later IHC shifted all to 1-3/8 inch shafts about 1943 to stop farmers having to have different couplings for different sized tractors. If one looks at harvester manuals from the 1930s and early 1940s one will see the pages of different PTO couplings to suit different tractors. The location for PTO shaft end to drawbar pivot was another issue and even IHC had to build adapters for the drawbars to meet the standard.
 

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