I found a used belt-driven 46" mower deck locally for almost free. I snagged a set of bevel gears off Ebay for cheap (they came out of the differential of a 21.5hp lawn tractor, so probably OK with the torque, but not sure how they'll hold up to heat from higher speeds). Here's a pic:
View attachment 32145
The counter-clockwise rotating tractor PTO connected to the left side of this (or a similar) differential gearset will give me 1) a downward shaft that spins clockwise (looking at it from the top...attach a pulley to run a belly mower...correct direction for most mowers, right?), and 2) a shaft out the back that spins clockwise...so, this should give me a clockwise PTO plus a clockwise belt pulley PTO as well. Seems like a workable solution. I'll have to build a gear case around it that would mount to the rear of the tractor, get all the couplers right, etc.
Dave_eng...what do you think? Those steel bevel gears were designed to turn slow...will they heat up/crack/fly apart if spun 540 or 1000 rpm under load? Making the gearcase oil-filled would help with heat dissipation...how much oil? (Worst case, maybe I need to find a set of automotive differential gears...? And maybe put a slip-clutch on the shaft that connects to the tractor PTO so if the bevel gears do break or jam it doesn't damage the tractor transmission?) Even if this isn't the exact right set of gears, a set of differential gears sure seems like a good solution, and should be reasonably easy to find used/cheap.
Your thoughts appreciated gentlemen...
Cheers,
Dave
With differential gear sets, the challenge is stopping the pinion gears so the torque comes out one side only. Your idea of having both backwards and forwards rotating shafts seems difficult as in my mind you can only use one at a time or the pinion gears just turn and no power goes out the other side.
I have no experience in welding up differentials to lock them but the engineer in me says welding on heat treated gears does not lead to long life.
Others may have done this with great success for stock car racing on dirt.
The bigger gears you use the better as then you are reducing the load they see.
One of the really tough rear 3pt hitch snow blowers for your size of tractor was made by McKee for several tractor manufacturers including Kubota and John Deere.
The blower had two bevel gears to transmit power at 90 degrees to turn the auger sprocket.
These gears run totally un lubricated and in the open with just a simple guard to keep fingers out. They will be running again this winter.
This is a picture of the gears.
This is the blower those gears are on.
My closest friend has had a B7100 HST which he bought new in the 1970's
The blower is just about as old.
The blower was designed to run at 540 rpm from the rear pto but my friend has always run it at a higher pto speed of around 800 rpm (my best guess) and there is no problem at all with the bevel gears after all these years and at a much higher speed than the blower was designed for.
I think in the sort of "back yard," design like this, the key is providing a lot of support for the shafts holding the gears so under load the gears are not moving about as their shafts deflect.
Also getting things attached to the rear pto and the mower deck pulley are challenges.
Shear bolts in the pto shaft have been a very reliable way of protecting tractors from loads imposed by implements.
The shear bolt needs to go on the implement end of the pto shaft not the tractor end.
I think you want to have a pto shaft in this connection to your tractor. It is all too easy to have a design which unwittingly imposes a side or up or down load on the pto shaft and it is not a good practice to do this. You fabricate something with these gears and attach it to the pto. To secure it to the tractor you drill some holes and use existing bolts. A bolt is like a screw jack and the force it can exert as it is tightened can be very high and you really don't even notice this and suddenly there is a snap and the rear casting on your tractor has a big crack in it.
This is a photo of a repair to my mistake many years ago. No warning just a loud crack and a piece of cast iron on the ground. I felt sick to my stomach.!!
I am not certain if you have seen these rear pto reverser solutions but here they are.
Item D goes over your pto shaft, gears lower the output and reverse it if needed and then another shaft goes forward under a tractor.
This next image is not of a Kubota but a very old tractor. I think the owner has been very clever in his use of sprockets to reverse the pto direction.
Mower decks on more expensive garden tractors have gearboxes on the mower deck. Many of these tractors have reached the end of their lives with electrical safety switch issues etc but their mower decks are usually a heavier product than a cheap garden tractor would have. In my rural neighborhood there is unlicensed small engine mechanic. His yard is littered with the left over garden tractors.
He does not use the internet and it is a word of mouth business. I think there are these guys everywhere. Big box stores sell garden tractors, no one wants to fix them when they did not sell them, repairs are expensive and they are junked.
If the mower deck already has a gear box on it, it wont matter if the drive for it comes from the front or the back of the tractor.
Making a drive system to come off the front engine pulley also seems do-able for someone with your skills. Now you have a drive at the speed mower decks are designed for.
This deck was on a semi commercial garden tractor.
The engine had a double wide or two pulley system on the engine which dropped to a lower level using V belts. At the lower level under the engine a shaft , driven by the two v belts drove the mower deck gear box.
Lots of things for you to contemplate and look forward to hearing what you decide to do.
Dave m7040
