Why 540?

[TerryR]

So the question still stands...Why 540? Why did the ASAE in April of 1927 decide that the PTO rotational speed was to be 536 +/- 10 rpm?

Yes, that is the question? Why?

I believe the early engine speed comment has merit and could be a good starting point for the ASAE logic.

One might think so, but what would the connection be? These old engines were used for a flat belt connection to the powered equipment. How does that relate to a shaft connection?

I have seen photos of a belt pulley on the rear of tractors. If it was driven by the PTO with a one-to-one ratio right-angle gearbox then having it turn at the same speed at the old engines might make some sense. Were the first PTOs used for belt connections rather than a shaft connection?

 

[k0ua]

Yes, that is the question? Why?



One might think so, but what would the connection be? These old engines were used for a flat belt connection to the powered equipment. How does that relate to a shaft connection?

I have seen photos of a belt pulley on the rear of tractors. If it was driven by the PTO with a one-to-one ratio right-angle gearbox then having it turn at the same speed at the old engines might make some sense. Were the first PTOs used for belt connections rather than a shaft connection?

When I was growing up our old tractor (Farmall Super A) had both a PTO shaft and a Belt pulley. They were both engaged when you engaged the PTO lever. The PTO was 540, but the belt pulley turned at 1157.

 

[Langanobob]

I found this on the infallible internet. Makes sense to me:

PTO's are 540 rpm because the original tractor designers in the 1920's and 1930's were trying to select a speed for their new PTO. They decided the McCormick reaper sickle needed 540 RPM and selected it. The whole world copied. Isn't that neat?

 

[LouNY]

So the question still stands...Why 540? Why did the ASAE in April of 1927 decide that the PTO rotational speed was to be 536 +/- 10 rpm?

I don't understand the 60 cycle electric motor explanation...the common speeds for AC motors are 1725 and 3450 rpm.

I believe the early engine speed comment has merit and could be a good starting point for the ASAE logic.

Electric motors speeds are determined by the number of poles;
16 pole 60 Hz = 450 rpm unloaded
12 pole 60 Hz = 600 rpm unloaded
10 pole 60 Hz = 720 rpm unloaded
8 pole 60 Hz = 900 rpm unloaded
6 pole 60 Hz = 1200 rpm unloaded
4 pole 60 Hz = 1800 rpm unloaded
2 pole 60 Hz = 3600 rpm unloaded
of course we shouldn't forget the Europeans with their 50 Hz power
12 pole 50 Hz = 500 rpm unloaded 50 Hz 3000 1500 1000 750 600 500
10 pole 50 Hz = 600 rpm unloaded 60 Hz 3600 1800 1200 900 720 600
8 pole 50 Hz = 750 rpm unloaded
6 pole 50 Hz = 1000 rpm unloaded
4 pole 50 Hz = 1500 rpm unloaded
2 pole 50 Kz = 3000 rpm unloaded

And then there are DC motors of all types and variations,
of course then we can start with VFD's for most any and all speeds.

 

[otlski]

Just wondering, in today's world some very good rpm meters but how did they know it was 540 that many years ago?

Hmmmm. Dont know the answer... but I could imagine having a known-ratio, geared-down mechanism, on the PTO and you counted the number of turns in say one minute. Then do the math.

 

[joeu235]

So the question still stands...

I don't understand the 60 cycle electric motor explanation...the common speeds for AC motors are 1725 and 3450

Its been a long time since I needed to know this so my facts might be a little off... but a/c induction motors have a speed in multiples of 60 with the number of poles affecting which speed. Motors in Europe run slower because they use 50 Hz and speed control on an a/c motor uses a VFD.

 

[4570Man]

Hmmmm. Dont know the answer... but I could imagine having a known-ratio, geared-down mechanism, on the PTO and you counted the number of turns in say one minute. Then do the math.

You’d still need to know the engine rpm. The only way I can think of using primitive technology would be to count the passes a flat belt makes around the pulley. The engine flywheel on even the old slow engine is too fast to count but it would be doable to count the passes a flat belt makes. Maybe they had a tool to measure how many times the plug sparks. But that wouldn’t work for steam or Diesel engines. Maybe they just used them with trial and error and never new the RPM.

 

[Langanobob]

You’d still need to know the engine rpm. The only way I can think of using primitive technology would be to count the passes a flat belt makes around the pulley. The engine flywheel on even the old slow engine is too fast to count but it would be doable to count the passes a flat belt makes. Maybe they had a tool to measure how many times the plug sparks. But that wouldn’t work for steam or Diesel engines. Maybe they just used them with trial and error and never new the RPM.

Mechanical counters have been around for a long long time. I even have an old one in a tool box somewhere. It has a rubber button on the end almost like a pencil eraser. You hold it against the end of a spinning shaft, count the seconds, a little arithmetic and you have your RPM.

Edit: I looked it up. Tachometers were invented in 1817 by a German engineer named Uhlhorn.

 

[mcfarmall]

I found this on the infallible internet. Makes sense to me:

PTO's are 540 rpm because the original tractor designers in the 1920's and 1930's were trying to select a speed for their new PTO. They decided the McCormick reaper sickle needed 540 RPM and selected it. The whole world copied. Isn't that neat?

I sure wish I had better internet skills! Do you have a link or website for this information? I think you may have hit the nail squarely on the head and driven it home too!

 

[RickB]

I found this on the infallible internet. Makes sense to me:

PTO's are 540 rpm because the original tractor designers in the 1920's and 1930's were trying to select a speed for their new PTO. They decided the McCormick reaper sickle needed 540 RPM and selected it. The whole world copied. Isn't that neat?

This is probably accurate since I seem to recall the first Tractor with a PTO shaft was an IHC product.
No, I don’t have a source or link to that dim memory nugget.