Author Topic: PTO speed reducer  (Read 725 times)

Offline pycoed

  • Jr. Member
  • **
  • Posts: 57
PTO speed reducer
« on: May 26, 2021, 05:22:12 AM »
I have recently resurrected a Japa 100 circular firewood saw which requires a tractor  PTO speed of 400rpm.



I want to use it on my Cushman Truckster, to keep the tractor free for other tasks.
Truckster has a Kubota 3 cyl of 20ish horsepower, so should run the saw OK. Problem is that the Kubota has to be throttled down to 800rpm to give 400 PTO rpm at which speed it produces about 1/2hp & the saw will only slowly cut up to 3-4.
So I need a speed reducer so I can run the Kubota at a speed to produce 15+ hp at a PTO  speed of 400. Somewhere around 1:2 reduction should do it

 I assembled the following potential bits from my scrap/stock pile :



2 FIAT Tempra rear hubs together with stub axles (30mm dia) & nuts.
1 6 pulley from the water pump of a Jaguar XJS that some scrote had burned out on the mountain behind our house about 20 years back.  I salvaged that pulley from a pile of molten aluminium when examining the remains.
1 3 pulley, source unremembered.
1 Cambelt tensioner from a FIAT uno (eccentric type)
1 crossbar from an electricity pole (4 x 3/8 galvanised angle)
1 piece of well rusty 3/8 plate source unremembered.
Small cast iron weight from an exercise set (about 4x 1.5) a road find IIRC.
Some 6mm SQ key stock.
M12 X 1.25 Allen Bolts
M8 Dexion bolts

I would have liked to use sprockets & chain, but didnt have anything suitable  in store (shed obviously way too small, dear), so a belt it would have to be. (no duplex pulleys either)
I actually bought <sob> a PTO extender about 12 long (F to M) to provide the input & output shafts for the reducer.

Started by cutting the PTO extender in half & welding each half to the rear of the FIAT stub axles, counterboring each for a pin to achieve concentricity.
Bored the 3 pulley to 30 mm
Bored the CI weight to 30mm & turned to make a hub for the 6 pulley & fixed with 3 Dexion bolts.
Ground some tool steel (broken endmill) to make a 6mm slot cutter & mounted  in a boring bar.
Used the lathe carriage to cut the internal keyways in both pulley bores. First time Id done this & it went quite well wouldnt pass a Rolls Royce inspection, but itll do  for this bodgeup!


Cut 6mm keyways in both stub axles in the mill & fitted keystock for pulley bores.
Cut a suitable length of the 4 angle to make the chassis of the reducer (12 abrasive chopsaw made short work of this). Chopped it about a bit with angle grinder.
Cut a suitable piece of 3/8 plate to weld to the angle ready to mount the hubs to the chassis.
Used a Sandvik 65mm holesaw to cut holes for the hubs in the chassis. Used about 200rpm in my inverter controlled Meddings drill press, lots of cutting oil & a 4mm chip clearance hole drilled beforehand on the circle went surprisingly easily.
Offered the hubs & drilled bolt circle to mount them could only find 4 suitable metric fine allen bolts, so 2 per hub it had to be to start.
Apart from machining suitable spacers from pipe & a few heavy washers, all was ready.


Assembled the bits, estimated a 29 vee belt would fit, mounted the Uno tensioner to the chassis. I didnt have an A29 belt, so more new bits needed! Ordered an A29 & A 30 belt , to be safe. Found the A29 was still a bit long once Id fitted it (the angles round the tensioner look a bit extreme to me), so Ive just ordered a couple of A28 belts. I dont know how long the belt will last Ill suck it & see once Ive started sawing. I suspect I may need to go to sprockets & chain, but well see.


Ive about a winters worth of logs ready for sawing & splitting, but all my log stores are full already, so next job is to extend  a pole barn to be able to store the stuff ready to be sawn.