Question about Double Cardan joints on PTO shaft

[Jim Timber]

I built a stump grinder that seems to swing the cutting head a bit more than the 30 degrees from center when raised and swung to the shortest side (the PTO shaft extended has no vibrations on the long side fully raised or lowered). Even though the drive train isn't under any load at this angle, there's a bit of vibration and it can't be good for things since there's a fair amount of rotational inertia with the 24" 3/4" thick wheel and cutters, etc.

I've struck out in finding an H-yolk for the Series 7 metric u-joints, but I have an idea for how to overcome that and that's what this thread is aimed at discussing.

What if you sistered up a pair of inside yokes for the same size shaft and made a H-yoke that way? It'd be dirt simple and assembling it would take all of 10 minutes if you took your time. I have drop shafting from building my shaft, so I just need the two additional yokes and could weld the whole thing together or bolt it. I don't like the idea of the H coming apart too easily, so I'm in favor of something more robust than the roll pins.

If this is a hare brained idea, I'm all ears. But I don't see why it wouldn't work other than possibly having excessive bearing cup to cup distance.

Thoughts?

 

[Jim Timber]

Nothing?

Eurocardan has boltable double yokes (as they call them), but they omit the 7 series and skip from 6 to 8.

Seems like if I milled off the majority of the sleeve side of the yoke I could shorten the length of the improvised H.

The only down side I can think of would be the shaft wanting to spin in an arc at the inside joint if the H is too long.

 

[CNC Dan]

Most of the double cardan joints I've seen have some kind of thingy to make sure the joints both flex the same amount. Without that I would wory that one joint would flex as far as it could, and the shaft would have horrible run out.

Could you use CV joints from the front axle of a four wheel drive truck?

 

[Junkyard Jim]

Google "Tom Woods custom driveshafts" He makes a double cardan that flexes 42 degrees, plus lots of other flexible shafts for jeeps mainly but will make them for anything. I know you want to make your own but just in case you decide to buy.

good luck with it.

 

[BigBoyToys]

You could give these guys a call and explain what you're trying to accomplish...Tom Wood's Custom Drive Shafts - Tom Woods Custom Drive Shafts Custom Driveshafts Specialist. I had them build me a drive shaft for a built Jeep. I think their prices are reasonable too.

 

[Jim Timber]

CV's are what have the center nub and those are substantially more expensive.

The problem I have with going to an automotive CV joint is that my clutch has an integral yoke on the input side (the output side being the gear box on the grinder). I have a FD4 clutch now, since the weasler single was either too loose or too tight, and the additional splined section increased the joint angles as well. I can have a reasonable amount of slip with the 2 disk and still get the job done. The weasler either slipped in the lightest of cuts or twisted the pto shaft - that was my experience with it in a single day.

The Eurocardan 2 disk has done 2 days work and only slips when I have about 18" of solid wood being attacked at the same time (through the center of a stump), and even then it's only in soft stumps like basswood (which happen to be the biggest on my property). Had I known the H-yokes weren't available for the 7's cross bearings, I would've gotten the 6 yokes instead, since the shafts are the same outside dimensions.

Other than the vibration at full sweep, the current configuration performs beautifully. Agri Supply has taken 3 weeks to ship my PTO shield (2 weeks to send the other parts), and when it arrived there was no outside tube bearing with it. They just informed me they want me to send it back, and they'll send me another. I complained about the snail's pace their shipping has been and that I want them to send me the missing bearing instead. We'll see what they respond with. My dealings with them thus far have been awful, and I'm not sure we'll be doing more business in the future.

I'm well aware of the dangers of an unprotected shaft. I'm the only one present when this is in use, but I still want the shield.

This was the second stump I ground with the machine, so my technique was still lacking. I need to do another video on something better to demonstrate the effectiveness and not have my hand shake holding it. She's nasty!