Tandem Disc Harrows and Pi

[jeff9366]

Tandem Disc Harrows and Pi​

Disc Harrow effectiveness is closely related to weight bearing on each disc or pan. The heaviest components, in total, are the Disc Harrow pans.

The weight of each pan is related to its area, its thickness and to its concavity.

The formula for the area of a circle is: A = Pi x R[SUP]2[/SUP]

Here are the approximate areas, in square inches, of common Disc Harrow pans:

Pan Pi R[SUP]2[/SUP] Area
14" 3.14 49 154

16" 3.14 64 201

18" 3.14 81 254

20" 3.14 100 314

22" 3.14 121 380

24" 3.14 144 452

Greater concentricity/dish requires more material so will increase differences above.

Thickness differences would increase differences above, but change would be linear. Larger diameter pans are usually thicker than smaller diameter pans.

Notched pans will be slightly lighter than un-notched pans of the same diameter, thickness, and concavity.

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

Tandem Disc Harrows commonly have 16, 20 or 24 pans, so the effect on total Disc Harrow weight increase rapidly with pan diameter.

We should de-emphasize Disc Harrow frame width and introduce the importance pan diameter when making Disc Harrow recommendations, especially when the question involves cutting/penetration.

***COMMENTS PLEASE***​

(Will someone explain the method to construct or introduce a data table to T-B-N?)

 

[Egon]

It depends on tractor size, disc type, and weight you can apply. any variable changes the outcome.

 

[Gary Fowler]

More to the point is pan thickness which also increases with size of the disk pan therefore more weight. Also in the equation is the spacer spools which can be a big factor in weight of the disc along with frame materials. All together, larger/heavier frame, larger/heavier disc pans, larger/heavier spacer spools make the disc cut more or less along with the diameter. Diameter of the pan limits the depth of cut the most. The disc can only cut 1/2 the disc diameter, minus the spacer spool diameter. So if you have a 18" pan with 4" spools, it can only cut 9"-4" for total of 5" whereas a 24" pan minus the 4" would be able to cut 8" deep. Per design requirements because of induced load, the frame on a disc with 24" blades would need to be stronger, thus heavier, than the frame of a disc with 18" blades.

Everything about the disc is relevant to how well it cuts, not just the pan diameters.

 

[jenkinsph]

"We should de-emphasize Disc Harrow frame width and introduce the importance pan diameter when making Disc Harrow recommendations, especially when the question involves cutting/penetration."


I agree with this and while I may recommend a width for a disk it is only one of many parameters to consider.


Gary makes some very good points in his post above, it is all relavent.

 

[bullbreaker]

Heres some info that's on my Howes owners manual.

 

[jeff9366]

If someone educates me on how to place a table in T-B-N posts I will add a column with actual pan weights from Agri-Supply's offerings, choosing a weight from the middle range of thicknesses and concavity and using notched discs. Pan thickness varies.

Replacement 18 inch discs are available in 3mm, 3.5mm, and 4mm thickness. Replacement 20 inch discs are available in 3.5mm, 4mm, 4.5mm, 4.76mm, 5mm and 6.35mm thickness. As you see, diameters and thickness overlap.

(Agri-Supply offers ***516*** replacement disc types on its web site. (What a great country!)

I may also add columns to show weight of (x)16 pans and (x) 20 pans to express total pan weight.

Gary Fowler: I have never taken a Disc Harrow apart. How much does a spacer spool for an 18" or 20" Disc Harrow weigh, just 'ballpark' ? I find 1" and 1-1/8" axles to be surprisingly light.

 

[jeff9366]

Everything about the disc is relevant to how well it cuts, not just the pan diameters.

I agree; however…..

For cutting the two most important Disc Harrow factors are weight bearing on the ground through each pan and gang angle adjustment. Weight bearing per pan will be mostly influenced by pan diameter, then thickness.

Concavity is a third factor. As pan concavity increases, 'float' increases, resisting penetration but throwing dirt wider.

Top Link length is important too, but Top Link is not a part of the Disc Harrow, per se.

 

[tmc_31]

jeff9366, interesting thread. I have been looking for a tandem for a while now. Choosing the right size has been a real pain. I want to use a tandem to plant food plots so I don't need a great big one. Maybe 8'-10'. I need to penetrate the ground as deep as I can and chop weeds. That said, weight is important. I have even thought about cutting down a 12' heavy duty drag type tandem to 8' (easier to get into tight plots and through smaller gates). I appreciate your point that the higher total weight per disk, the better ground penetration you will have and also that most of the weight of the plow is in the disks themselves. I also appreciate your explanation on the effects of concavity. Since I am putting in new food plots where penetration and ability to chop weeds is paramount, less concavity will be better that more. (my new food plots will first be chiseled then disked, seeded and culti-packed).

I was looking at Agri-Supply's offerings, (good prices on disks by the way) and I couldn't find the weights of the disks that they were offering. I am leaning towards (as I said) an 8' tandem with 20-20"X6mm blades with a 2.5" concavity (I still could use some guidance on the correct concavity for what I am trying to do).

I for one, would appreciate your posting a table. I wonder if you could create a table in Excel (or any spreadsheet) then convert it to a .jpg file. It could then be easily imported into a tractorbynet post using the "manage attachments" utility in the Advanced posting section.

Again, thank you for starting this thread. Hopefully it will degenerate into a discussion on how to choose a tandem disk.

Tim

 

[jeff9366]

I want to use a tandem to plant food plots so I don't need a great big one. Maybe 8'-10'. I need to penetrate the ground as deep as I can (my new food plots will first be chiseled then disked, seeded and culti-packed).

I was looking at Agri-Supply's offerings, (good prices on discs by the way) and I couldn't find the weights of the disks that they were offering. I am leaning towards (as I said) an 8' tandem with 20-20"X6mm blades with a 2.5" concavity (I still could use some guidance on the correct concavity for what I am trying to do).

I for one, would appreciate your posting a table. I wonder if you could create a table in Excel (or any spreadsheet) then convert it to a .jpg file. It could then be easily imported into a tractorbynet post using the "manage attachments" utility in the Advanced posting section.

In my experience in Florida, food plots do not require deep preparation or fine tilling, although it might be nice to do both. Deer and Turkey plot seed mixes are strong germinators and the seed is cheap. I refer to "scratching in" food plots with a Disc Harrow, then seeding. As I generally plant both Spring/Summer and Fall/Winter plots the ground is disced twice per year. So, with cheap seed, I disc, then sow. However, I do have a Cultipacker and I run it over the planted seed without fail.

I have ordered parts from Agri Supply in the past. When the freight is calculated, the product weight appears. I may call in to double check weights on the few discs I want for examples, or I may find weights somewhere else.

"I was looking at Agri-Supply's offerings, good prices on disks by the way, I am leaning towards an 8' tandem with 20-20"X6mm blades with a 2.5" concavity (I still could use some guidance on the correct concavity for what I am trying to do)".

I think you are "right on" with what you are considering. Just keep the Disc Harrow width a bit narrower than your tractor tires if you have to maneuver your tractor and DH between trees, boulders or other obstructions. I have never seen pan thicknesses nor concavity listed in the marketing materials for any Disc Harrow for compact tractors but that does not mean the information is not available from the manufacturer via telephone. I am sure you are planning to order notched pans front and rear.

How do I convert an Excel spreadsheet into a .jpg file?

You may have seen the thread I created on choosing Disc Harrows, link following.

http://www.tractorbynet.com/forums/attachments/308251-disc-harrow-selection-18-45-a.html?highlight=

 

[tmc_31]

I saved this Excel spreadsheet as a .pdf file and them from Preview (I am using a Mac) I exported it to a .jpg file. The .jpg file can be uploaded to tractorbynet posts. Kind of a convoluted way to do it, but it works. I tried it with Adobe and it wouldn't let me save it or export it to anything but a .pdf. If you can't find an easy way to make the conversion, send me the .xls file and I will make the conversion for you. I think you can send the file by PM. If not, let me know and I will send you my email address.

I am planning to put notched disks on the front for sure, and maybe on the back too. Makes sense that it would do a better job of chopping up the vegetation with notched disks on both the front and back. Hadn't thought about that.