Disc Rule of Thumb?

On the spacing issue, I do question whether a blade moving 7.5" of soil requires the same hp as a blade moving 9" of soil, just maybe one has to factor in spacing.

With the exception of the Bush Hog offset, and that is another class of disk, as was your John Deere PKH. Those 5 tandem disks I bought in my lifetime all required roughly 1.25 hp per blade. If you calculate the hp by the foot, it comes out quite different. I'll let you do the figures for yourself. My point is 7.5" spacing pulls much harder by the foot than 9" spacing. You openly admit, you've never had anything but 9" spacing.

Remember also a disk the had 18" blades when new, and is now worn down to 16". That will not be as effective as a new 16" blade. I'm not saying it's worn out. If your buying just be aware of what a new blade looks like. The effective concave is near the outer rim of blade.

Now getting back to what I said, that being 16" to 18" blades required 1.25 hp per blade. I guess the exception would be primary tillage disks, but not many of them are equipped with 16" or 18" blades.

Folks get on here chirping up about how much harder and offset pulls, what they seem to forget, most offsets have 24" to 28" blades. I know, I had a 246 Bush Hog 24 x 26" blades and it pulled almost as hard as my regular tamdem Bush Hog with 88 x 20" blades. I tried a 88 blade offset with 20" blades, very little difference between it and the regular tandem. Where the difference comes is the difference between primary and secondary tillage disks, and I've seen both in regular tandem or offset version.

I've also yet to see a heavy frame disk equipped with 16" or 18" blades

Dealer told me to figure on 6 hp per foot of cut and that my tractor will never pull it.

We'll see when this latest snow clears out 'cause I've got weeds comin' like crazy. :>(

Allan

Yeah, I "think" it's gonna work, emphisis on the "think" part. I turned the screw up on 'er a little last year and it seems to pull strong.

HOwever, always a bit "nervous" whenever I pull a stunt like this tho.

If it doesn't handle it, guess I'll have to drag that toy clear back to town again. :>(

Allan

Those JD discs sure cut nice, but they just can't compare to the way the IHs level the ground.

Allan

For what around here we call an "offset" disk (2 gangs/or axles, front throws right rear throws left), blades/disks are about 22 or 24 inches, you need 10 PTO HP per foot of cut.

What we call "tandem disks" (4 gangs in shape of X) , with blades/disks of about 16, 18 or 20 inches, require a lot less, maybe about 5 HP per foot.

For a "disk plow" which has about 30 inch disks each mounted on its own strut (no common axle thru center of disks) needs about 14 HP per bottom/disk/blade, each one of which cuts about 11 inches.
Tom

Link

Rod