Renze said:
Hope my prediction doesnt discourage you, but i think the wheel will break off the shaft first time you put it into the ground, or goes wobbling. It needs more steel in the center to keep it going straight.
I agree with Renze, Unfortunatly. I don't think there is enough strength in the wheel. Every rotary wheel type trencher I have ever seen has a wheel mostly comprised of a steel plate, a big thick steel plate! There are 2 reasons for this.
1. Overall wheel integrity. As the teeth hit buried rocks there is a lot of shock load and the wheel must withstand this. The larger the teeth, the more this effect will be felt as the larger teeth take a larger bite. Do you think you could take a sledgehammer to this wheel repeatedly and it would still stay intact? Those are the kind of blows that it will receive when it engages rock in soil. Flexing metal fatigues. I think your wheel will flex when it comes under load and fail.
2. F=MA(Force = Mass X Acceleration). A large solid spinning steel disc has inertia. This is why brushhogs work as well as they do on large brush stocks and small trees. As a tooth hits a rock, the inertia in a solid wheel trencher helps to dislodge or break thru the rock. A open or spoked wheel has lower inertia so when the tooth engages the rock, the force is transmitted back thru the wheel structure(this will cause the flex) and the structure, chain, gearbox, PTO shaft and PTO output drivetrain must absorb this feedback.
Your paddle teeth are perpendicular to the shaft axis. There are 3 stress modes for material. Tension(pulling) the strongest mode. Compression(pushing)the second strongest. Axial(sideways or bending load) which is the weakest. I would say that your teeth and the spokes at some point should be angled in the direction of rotation. Look at them like shovels. Do you drag a shovel across a pile with the handle perpendicular to the surface/direction of travel, or do you angle the tip into the material so the blade scoops into the material? That is why most shovel blades are angled where they meet the handle so we can get a proper angle without having to stoop over too much to use the shovel. The force of these teeth digging in are going to try and bend the spoke and try and pass the forces along to the other spokes with the straps. Since not all the spokes run to the center of the hub, some will compress the intermediate ring as the force bends them backward. The outer corners of the paddles will probably start to bend first as they are unsupported and purely side loaded. A "Ditch Witch" works so well because the teeth are well supported like that of a chainsaw and the drive system is nearly totally in tension(strongest mode).
I would reccomend you remove it while it is still neat and use it for yard art before it pretzels and possibly injures you or damages the drivetrain or tractor. I would then reccomend you go to a steel supplier and have them cut you out a 30"-40" diameter disc of 3/4" steel plate. Into this plate cut notches in the edge angled into the direction of rotation at least 45 degrees. You can also drill holes around the rim and add grade 8 bolts or additional bolt on side paddels. This way if you bend or break one, they can be replaced without having to replace the entire wheel.
If you do run this thing in the ground, please go slow, because when it lets go, it is going to entangle itself with the safety guard and wad itself up in a gross visious fashion.
Good Luck
