I've watched the 2nd video of the failure over and over and from what I can see the self aligning bearings that failed were in the link between the eccentric and the top arm. Do I have that right?

The top bearing could be a heim joint since it doesn't rotate much. The bottom bearing does need to rotate with the eccentric, so maybe a better bearing? Or spacers/washers to keep them contained?

I watched it some more in slow playback and it appeared to stall the motor as I can see your left foot didn't move until the carnage had already happened. It also looked like the bottom bearing had slid rearwards a bunch before the carnage.

Some way to contain the bottom bearing is needed.

Yes Bill, the self aligning bearings are in the link. I think a heim rod rod end would do it or tie rod end from a truck for the upper end with a self aligning bearing on the crank end.
It did stall the motor, and good thing I was barely idling, or pto shaft twisting would be next.
The undercutter works well without power, but the inherent problems of tops bunching up occasionally and creating tangle, or a clot of dutch clover lifting the cutter bar remain. The motion of the bar helps create a flow of dirt and plants over the cutter without tangles.

I had the pto on it's lowest speed and was hardly above idle on the engine, but I think these bearings are not a good choice for reciprocation. I would be better with a sleeve bushing. The tractor will still pull the broken undercutter at low idle, and I found that speed is not your friend as the material flow gets buggered up past a certain point. Sort of no difference to any other implement. they all have a best operating speed.

A bit spendy, $260 from McMaster. It is a much better version of a 1" heim joint.

What is the diameter of the eccentric?

I think your original idea of tierod ends is the direction to lean except that they do not have constant rotation in service. They will wear prematurely, but 2-3 hours a year is not abuse considering what a joint will see over a lifetime on a truck, and you already have a few laying around.

on to 2nd design. I can see where the movement of the cutting bar helps go thru the soil though. It sure looks like you are getting a good body shaking though. Good way to mix up your stomach contents to better process your lunch. :D

Any worries about the vibrations doing damage to the tractor though? The front end seems to be bouncing quite a bit. Would hate to see the front wheels break off due to all the jumping up and down.

If you had live hydraulics, or maybe run a hydraulic pump off the PTO, and then use a Hydraulic motor to run the Eccentric drive, you could then use a flow valve to vary the speed of the motor. Not sure of your resource pile of hydraulic pumps and motors. Other down side is another possible problem of leaking Hydraulic oil in your farm field if something breaks.

It is a small tractor and that sure contributes to the front shaking. If it was a 30 to 50 hp tractor, it would have enough mass to stop the bounce. This is 1100 lb and 20 hp. I could have tried more forward speed and keep the pto speed down. I never had time to experiment before it blew out.
My resource pile has some triple pumps, and a complete hyd drive from a cement mixer.
I do have a pto pump also. No hyd motors at present.

At this point, including the pto shaft, and various other drive experiments, the cost is around 500 bucks. I think that with the improvement in how it cuts with a stationary blade, I should mark this down as a failure and just go with what I have now.
The previous stationary 28 inch cutter dragged like a dead horse. This one, although wider by almost a third, is ok to pull.

Change the driven portion to only a shaft with the support bearings and an eccentric plate, then spring load the actuating arm/lever with a roller bearing on the end to keep it in contact with the eccentric? Use a bearing with a slightly curved face instead of a normal flat one?

https://www.shopfloortalk.com/forums...4&d=1659047205

It seems to me a potato digger style would bring the whole plant to the top for easy picking. All you would need is a 15 degree slope to raise the soil and plants and lrt them fall off the back. Not sure your tractor is big enough to pull one though.

I have a steeper angle on this blade than I did on the old one. It don't make sense, but that is maybe why it pulls a 39" knife through the ground at an idle, and with the 28" knfe it would spin tires if the diff was not locked.

would vibration do the job?