Why do PTO drive shafts have grooves?

[Number15]

Imagine if your PTO shaft uncoupled when using an implement. Perhaps carnage.

 

[k0ua]

Uncoupling of the PTO shaft while operating has happened. I have never seen it happen, but from what I understand from those that have is that it is quite a show and real interesting until it stops flailing around and threatening your life.

 

[RickB]

Uncoupling of the PTO shaft while operating has happened. I have never seen it happen, but from what I understand from those that have is that it is quite a show and real interesting until it stops flailing around and threatening your life.

Depends a whole lot which end becomes disconnected. It's not usually too traumatic if the tractor end comes off, especially when the shaft angle is limited by the implement 3 point a-frame. When the implement end comes off and the shaft is still powered that can get ugly fast.

 

[ptsg]

I had one PTO shaft come off but as Rick said, it was on the tractor end and didn't cause and damage. The implement was a spading machine, which runs at low RPM anyway. If it was a mower, would probably bounce around quite a bit but should stop shortly after.

 

[Wagtail]

I had one PTO shaft come off but as Rick said, it was on the tractor end and didn't cause and damage. The implement was a spading machine, which runs at low RPM anyway. If it was a mower, would probably bounce around quite a bit but should stop shortly after.

I also had this happen... because it was the very first time that I had ever attached a PTO implement = 'rookie mistake' or, as we say in Aus, 'tip for young players'.

I didn't have the shaft angle correct and struggled (cursing a blue streak!) to even get the shaft on. I finally did, but didn't advance the shaft to the 'lock' position (or as the OP asks, the 'groove'). It's only happened the once, thankfully no damage and I learnt my lesson.

I now lanolin spray the shaft & the PTO, level the implement shaft to the PTO, advance the shaft onto AND past the PTO 'groove', release the pin/collar and pull back the shaft to lock it into the 'groove'.

 

[ptsg]

I also had this happen... because it was the very first time that I had ever attached a PTO implement = 'rookie mistake' or, as we say in Aus, 'tip for young players'.

I didn't have the shaft angle correct and struggled (cursing a blue streak!) to even get the shaft on. I finally did, but didn't advance the shaft to the 'lock' position (or as the OP asks, the 'groove'). It's only happened the once, thankfully no damage and I learnt my lesson.

I now lanolin spray the shaft & the PTO, level the implement shaft to the PTO, advance the shaft onto AND past the PTO 'groove', release the pin/collar and pull back the shaft to lock it into the 'groove'.

In my case, I had just bought my first crawler tractor that came with the spading machine. The PTO shaft that also came with it had the locking pin on one end rusted solid all the way in.

I was eager to test the thing out and just put the faulty end on the tractor side and went for it. I knew nothing major would happen and I still managed a 50 meter pass without the PTO shaft falling off.

 

[JWR]

Oh, you mean THAT groove! At first I could not figure out what you were talking about. As most have already said the purpose is to enable some locking device to prevent the PTO driven shaft U-joint from sliding off of the PTO until you want it to slide off and release the locking mecjhanism. The two common locking mechanisms both involvbe B-Bs that match the grove and spring loading that sink the B-Bs into the grove, commonly in the PTO sleeve of the implement's U-joint. The two common types are the twist a collar and release and the pull a collar and release.

OBTW I assume there is a standards organization (SAE or similar, whatever that is for AG equipment) which standardizes the depth, radius and distance in from the end of the PTO shaft where the grooves are located.

 

[miniceptor86]

And while your book shows a variety of dimensions the size is standardized for ag tractors’ 540 and 1000 rpm PTOs

 

[Bentrim]

Way back when tractors first came with PTO there was no standard and manufacturers seemed to settle on 1 1/8 6 spline. Low horse power and 540 not much of an issue. When the PTO became more popular there were standards established so every body could hook up their brand tractor to any brand equipment. That is when the 1 3/8 6 spline 540 RPM standard was established for the lower horsepower tractors. Then for the higher horsepower tractors the 1 3/8 21 1000 RPM spline shaft was adopted. By the way the if you understand electric you know that the 1000 RPM drives can be smaller and carry power easier than the 540. Even yet more power was being produced that the 1 3/8 shaft could not handle safely, then the 1 3/4 shaft was used.
As time went on and probably accidents with the PTO shaft coming off. Better and some times what they call safer ways of keeping the PTO shaft on the tractor output shaft were "invented". A lot of the old timers had no retention groove and were retained by putting a bolt or cotter key thru the joint and shaft. It worked except you had to put the joint on the shaft correctly or the hole didn't line up---take it off and try again. And probably with shields removed or non existent the bolt became a whirling hazard.
Then someone came up with the idea of the push pin where you take your thumb push the button in and push the joint on the shaft until the pin pops back out. Still had a "pin" sticking out that could catch what ever got near it. Although they were usually trailing and made it harder for the to hook something. Some pins were retained when the tail of the pin went thru the yoke with a ring that would squeeze shut, and you were able to pry the ring apart or open it if the pin needed serviced. The other kind fit in the hole, did not go thru but was peened in to keep it in. But no matter they could not come out when the yoke was installed on the shaft no matter which style was used,
Then safety conscious "person" (just to be kind) invented the spinning collar which just about makes it impossible to keep from cussing up a storm when trying to hook it up. They don't use a pin anymore but the collar released balls that just like the above pin fit in that groove in the shaft.
Then some enterprising person developed the adapter. Yep 1 3/8 six spline to 1000 21 spline and the other way around. Farmers loved this idea because they could use a big tractor (1000RPM PTO) to run self unloading wagons (540 RPM)during silage making. They just ran the tractor slower so not to destroy the wagon.
Most of the old Ford N series and some of the early Fergusons and some other makes were new with the 1 1/8. Some adapters were made so 1 3/8 implements could be used. Some were just a sleeve, some were made as an extension, you can even get a conversion shaft to make it 1 3/8 and since they used a transmission driven PTO some were made as over running clutches. Over running clutches will allow the rotary mower or any "flywheel" type implement to run free when the tractor stops ground travel. Without one you just might wind up on the wrong side of the fence! Or thru the barn wall.
Just for an aside I have seen 80 horsepower twist a 540 shaft, not break but twist.
I know without pictures it is hard to explain but I hope it gives you a little better understanding and a little history of the PTO.

 

[Wyobuckaroo]

Didn't some of the very early tractors with a PTO have a hole through the shaft so you could pin the mating parts together ??