Correct lengths for PTO shafts

[icehorse]

I just got my new drum mower set up and working yesterday, hooray!

But as I was doing this I had to cut down one of the provided shafts, and so I went down the rabbit hole of exactly how long these shafts should be.

It seems there are two big considerations:

1 - How many inches of play should there be so that the shaft can shorten when in use, and not smash into the tractors PTO shaft.
2 - How many inches of overlap between the two steel shafts is a safe minimum when the shaft is most extended?

The drum mower has two PTOs (what fun!), and I'm a bit worried that the shaft that connects to the mower itself has only about 4 inches of overlap.

If it IS too short, I'm wondering about getting one of these PTO extenders, Are they any good? Any recommended brands?

https://www.amazon.com/Upgraded-Ext...d2lkZ2V0TmFtZT1zcF9zZWFyY2hfdGhlbWF0aWM&psc=1

 

[North Idaho Wolfman]

DO NOT use PTO extenders they can damage bearing very easily.

4" min overlap on the PTO is fine.

 

[Russell King]

And if you want you can probably just buy new tubes for the PTO and replace what you have. Then you might have to cut those down!

 

[MapleLeafFarmer]

If you like the advice Messicks gives out they recommend min. 6" of overlap when fully extended to handle the torques and 2" buffer from bottoming out when compressed to avoid damage. I wouldn't argue those rec's on this end.