Tandem Disc Harrows and Pi

[jeff9366]

Since acquisition I have adjusted my Howse Disc Harrow so that front gangs are set at an angle and the rear gangs are set two adjustment holes "straighter", then experimented with adjustments off this relationship. From my observations most north Florida Disc Harrows are set in this relationship.

Earlier this week I was guest conductor on a Deere 5103 / 50-hp / 5,000 pounds pulling a Deere/Frontier 20" Disc Harrow with lever adjustment. The owner, who has farmed part-time in my area for thirty years, has his front gang "straight" and his rear gang angled, a recent change I was told. It tilled really well but he has been amending his soil with manure for years and it is exceptionally friable. When I next see Andrew, who is suffering from Shingles, I will discuss his DH settings with him and may experiment with his basic setting, which is the reverse of my basic setting. Before I bought my DH I thought Andrew's adjustments, straight front (cutting) and angled rear (mixing) made sense in theory.

I love to experiment, seeking implement/soil nirvana for each implement.

 

[CNC Dan]

The point of this exercise is to show how rapidly pan weight and therefore pan penetration, increases with diameter.

But the disc is larger in diameter, so there is more of the disc edge in contact with the soil per inch of soil penatration. I think that cancels out the increase of weight from the increase in diameter.

 

[tmc_31]

Hey jeff,

You seem to have developed a good bit of information and expertise regarding tandem disks so maybe you can answer a question for me. What is the optimum speed that a tandem should be pulled and why

Thanks,

Tim

 

[jeff9366]

A Tandem Disc Harrow is a tiller, which mixes the soil. In the process it also levels the soil. One gang, usually the one nearest the tractor, throws soil out. The other gang, usually set wider and usually the rear gang, throws soil in. In the process soil is mixed and soil profile is leveled as soil is moving in the air as the pans traverse furrows.

The Disc Harrow should be pulled fast enough so soil thrown out, then in, is equal. Usually that is a "brisk" pace. For my tractor/Disc Harrow combination, that is HST medium range, plus some hand throttle.

Cannot give an exact speed. Optimum speed is dependent on user selected Three Point Hitch depth setting, user selected Top Link length, user selected gang angles, pan concavity, pan spacing, pan penetration, depth of plow furrows being crossed, if any; crop residue, soil type, and soil moisture.

Good?

 

[jeff9366]

But the disc is larger in diameter, so there is more of the disc edge in contact with the soil per inch of soil penatration. I think that cancels out the increase of weight from the increase in diameter.

Pans have an edge like a knife. (serrated knife?)

When you carve a roast, what works best? A large, heavy, carving knife or a small, light, paring knife?

 

[CNC Dan]

Pans have an edge like a knife. (serrated knife?)

When you carve a roast, what works best? A large, heavy, carving knife or a small, light, paring knife?

Just being pressed into the roast, the smaller knife would have a smaller length of cut, so more pressure. But I don't think thats a good analogy for a disc harrows action.

If you wanted to penatrate something tough , would you use the tip of a knife, or the edge?

The tip of the knife would concentrate the force on a very small area. The edge, though sharp, would apply the force over a larger area. This is with the same overall force for both situations mind you.

Note also that with a harrows disc rotating as it goes allong the soil, you don't get the slicing/sawing action that would be used with a knife. More like a pressing/rolling motion.
But then there is the angle of the disc axle to to the direction of pull. Combined with the amount of dish the disc has creates a plow like action.

I'm not sure what would be a good analogy to a disc harrows cutting action.

But I just wanted to point out that your calculations weren't taking account of the larger edge contact a larger disc would have.

But I do think the larger/ thicker/ heavyer discs will work better.

 

[jeff9366]

The long carving knife has more edge in contact with the roast. Carving knife cuts better because of weight.

There is no down pressure from the 3-Pt.; gravity is the only down force, which is why pan weight is key.

The leading edge of a larger diameter pan (50% of ground contact) will present some increase of resistance to penetration with increasing diameter but it is a small increment relative to the increase in pan weight with diameter. The trailing edge of the pan (50% of ground contact) is being lifted and presents NO resistance.

Pans are all edge; no point. Notched pans are pretty good slicers, that is why they are used to cut in crop residue in preference to smooth pans. "Slicing action" occurs as the Disc Harrow makes second and succeeding passes over the ground; just an interval between slicing strokes.

Debates are good here, provided they yield more light than heat.

The readership will select from information presented.

 

[jeff9366]

Since acquisition I have adjusted my Howse Disc Harrow so that front gangs are set at an angle and the rear gangs are set two adjustment holes "straighter", then experimented with adjustments off this relationship. From my observations most north Florida Disc Harrows are set in this relationship.

How are "y'all" in other parts of the country setting your Tandem Disc Harrows? What are your objectives when setting them? What is your soil? Do you Fall plow? What other settings have you experimented with? (Let's stay on Tandem Disc Harrows, please.)

 

[tmc_31]

A Tandem Disc Harrow is a tiller, which mixes the soil. In the process it also levels the soil. One gang, usually the one nearest the tractor, throws soil out. The other gang, usually set wider and usually the rear gang, throws soil in. In the process soil is mixed and soil profile is leveled as soil is moving in the air as the pans traverse furrows.

The Disc Harrow should be pulled fast enough so soil thrown out, then in, is equal. Usually that is a "brisk" pace. For my tractor/Disc Harrow combination, that is HST medium range, plus some hand throttle.

Cannot give an exact speed. Optimum speed is dependent on user selected Three Point Hitch depth setting, user selected Top Link length, user selected gang angles, pan concavity, pan spacing, pan penetration, depth of plow furrows being crossed, if any; crop residue, soil type, and soil moisture.

Good?

Well... I was sort of hoping I could get a little more definitive answer from you, kind of like 4.56278mph or thereabouts. But, I get what you are saying. I have pulled several sizes of tandems with my tractor over the last several years. Ranging from 14' down to 6'. With the 6' I can go as fast as I can stay in the seat. With the 14' I can get about 3mph at full power. I pulled a 12' plow (tandem disk) last year and was able to get 4.5 mph out of it. I realize there can be a lot of variables when measuring the effectiveness of the plow but for all intents and purposes each of the plots I was working was very similar. Clearly the 14' is too much. Originally my intent was to find the largest tandem that I could pull at about 5 or 6 mph. I think I can do that with a 10' plow. I have kind of settled on a 8' plow for other reasons (such as transporting, getting through gates etc.).

I also run a tandem as flat as I can so that the front and rear gangs engage the ground about the same. It never occurred to me the bury the front gangs. I would think that you risk damaging the plow if you go overboard with that. Could be wrong.

Tim