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Implement Alley Discussion Forum

HP vs. Harrow Size

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03-02-2012 15:33:40

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Is there a general rule of thumb for how much hp it takes to pull a set of double gang disk harrows? Like 5 hp per ft or something? I have a Farmall 504 RC diesel and was wondering what it could pull well. I have a Oliver double gang drag disc harrow that is 8 ft wide with 16 inch disks. I cant imagine that would stress it much. But what could it take? Thanks

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Deere Scotty

03-05-2012 03:40:34

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
Disk weight, Blade size, blade spacing, & soil type along with moisture are major factors in required horsepower. If You have hills to climb, add that too.


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03-03-2012 16:09:18

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
gtski I dont see how u coulda wore out a couple of IHC discs. Ive got the first disc I ever bought at age 17 at St Joseph Mo IHC on 4th St. They were moveing to another location and selling out alla there old machinery. They had 2 discs like mine. One for $50. It had rough blades, and a good one for $75. I bought the cheap one. When dad looked at it after he got off of work, he told me to buy the better one, which I did. Its a IHC 16ft single that origionally had 3ft bat wings on the ends. It is a heavy disc, Dad had a JD the same length and he said that the IHC was a heavier disc. Ive pulled it with F-20s, F-30s, M, IHC, A, B JD, CC Case, Never had a problem till I got down here in Okieland. The Case has narrow tires, and it was hard to turn it around. The F-30 I had down here never knew it was behind it. I always let the drawbar swing free which helps immensely on turns.

I broke a housing when I put new discs on it around 20yrs ago. Last year, I broke 2 discs on the R end. I had to pull the section that had the broken housing. The steel axle looked as good at that point as it did at other points that had full housings. Id say this disc is good for another 50yrs. Id like to straighten the outside brace bars, but thats not such an easy job, so,. That being bent comes from not haveing a swinging drawbar,
I DO got to remake the lever that lets the disc open and close. It finally broke a couple years ago, and i remade it. When I flipped the disc over on its back to get at those 2 broken discs, I broke it again. It has all square head bolts and nuts, and I tried to replace all the hex head I had put on it over 50yrs.

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03-03-2012 19:44:19

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 Re: HP vs. Harrow Size in reply to Farmallb, 03-03-2012 16:09:18  
When the 16" blades are down to 12" and the bearings and spindles are worn through i have to say they were worn out. Those discs were 8' tandems from the 1930s just like the tractors. Only thing the 20s lacked was a swinging drawbar to make turns easier.

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03-03-2012 14:34:38

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
It has been 54 years since I have seen a disk as you are describing. A tandem disk is measured by the back gangs and a 7 blade on a side would be 8', a 6 blade would be 7'. Then the single disk measurements were the same as the front gang on the double disk so measuring 8' on the front would be called a 9' on a double gang. And that disk was very close in weight to the horse disk of the same size. Now that disk could have been made in 6 blade on a side up to about 10 on a side. the 6 or 7 would have been sold for the Oliver 60 tractor with a max of 18 pto hp and a Allis C would have been 23 max pto hp so no reason a Allis C could not have handled it, both tractors were designed to pull a 2-12" plow. The first disk Dad bought for the 44 2N Ford was a Dunhan and he traded it on a Oliver and it was pulled on many a acre with that Ford in ground it had just plowed with 2-12" plows. After Dad bought a second tractor in the spring of 1957 he traded that Oliver on a John Deere 6 blade on a side (7 1/2') KBA model in what was considered at that time a heavy disk disk and pulled it with a 38 JD A or later with a 49 JD B & 28 hp and later I pulled it with a 46 JD B with 20 hp. Now you go to a heavier disk like a McCormick No. 37 on a 7 blade on a side (8' 8" cut) like was sold for use with that tractor you have we pulled ours all the time with a 38 HP JD A ( disk is curently pulled by 5 belgin horses) it would be an easy load, a 8 on a side at 9'10" would be more what your tractor should handle in fresh plowed ground provided it is properly weighted and with dual tires. A disk of the weight of yours you could pull with your 46 hp tractor (equal to a Super M in power) at easly 12' wide. The ones that are saying you need way more power are probably too young to remember those disks. And that disk with 16" blades would only cut about 4" deep not the 6-8" they are thinking about. That tractor should handle a 3-14" plow that pulls twice as hard as the 2-12" plows the tractors that disk was made for pulled so even at a higher speed you should have no problems and that is with no extra weight or duals. Just don't because you have enough tractor to do it try to put a second implement in behind and pull the disk apart, that is what happened when Dad got rid of it and that was with a tractor of 20 less hp than what you have..

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03-03-2012 14:13:59

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
I don't know what most of you were pulling in but we used 8' IH drag discs behind F-20s and SC Cases forever and had no problems in plowed ground. You don't need full angle to level mellow plowed ground. Usually pulled two 5' spike tooth harrows behind the disc. This was in LaSalle Co. Illinois that last year had the top corn ave. in the nation so pretty good soil.

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03-03-2012 09:48:06

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
You shouldn't have a problem with that old disc. They are relatively light weight compared to the modern discs and you "don't" have to leave it set at full angle either. If you are in fresh plowing , only set it at half angle. There is no formula as you can see , too many variables.

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03-03-2012 07:31:32

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
I pulled a 8ft. I-H wheel disk with my RC504 gasser. It did OK with it but it was about all she wanted with a 8ft. packer hooked on the back of the disk. I'm thinking the rule of thumb was 2.5HP per disk blade. I'm now pulling the same disk with a 41 HP DieselMF and would like to have a few more HP although traction without the tires loaded is the main problem I have now. I'm talking on plowed ground. They both do good disking corn stuble or hard ground.

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03-02-2012 20:42:43

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
Don't know how heavy an Ollie disc is but we wore out a couple 8' IH drag discs with an F-20

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03-02-2012 18:28:30

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
Well, it depends on whether you are using drawbar or engine horsepower. I think 4-5 hp per foot is right for drawbar hp, and 5-6 hp per foot for engine horsepower.


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03-02-2012 17:22:12

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
45 hp tractor like yours should match up pretty good to a 8 foot tandem disk. Will disk up bean stubble or cornstalks easily in fall, won't know it's there. Will be all you want in spring in loose plowed fresh ground, wouldn't want any bigger.

Some disks are set with bigger blades, more spacing between blades, and will pull harder. Some are more of a finishing disk, closer spacing and the blades are worn down, it will pull easier. So, we can only do general sorta guesses for you. :)


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Paul from MI

03-02-2012 16:59:19

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
Like rr says a 7ft. tandem pull type disc is about right for a roughly 25 hp two plow tractor. If you were only discing corn stalks in the fall you could pull more, but not on plowed ground. That's with the older lighter discs, a newer heavier disc with wider spacing between the discs would pull harder. Personnally I would err on the small side. You can do a good job of discing with a smaller disc that you can set to cut deep when you want, but if you have to set it light to be able to pull it the results aren't near as good.

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03-02-2012 15:39:07

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
Depends whether you're discing plowed ground or something like corn stalks. Back in the day,we found that an 8 foot disc was too much for a two plow tractor in plowed ground. Something like a Farmall H,Case SC,Oliver 66,JD B,seven foot was all they wanted.

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charlie M

03-02-2012 16:54:07

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 Re: HP vs. Harrow Size in reply to rrlund, 03-02-2012 15:39:07  
I pull 8' with my M and its plenty for it. My dad used to pull 10' with a W9.

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03-02-2012 15:38:27

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 Re: HP vs. Harrow Size in reply to JHubnuts, 03-02-2012 15:33:40  
It largely depend on the type of land. Clay pulls much harder than sandy loam. Hills pull harder than flat ground, and some discs just pull harder than others. More weight, smaller disc blades, ect. I would say, as a general rule, a 20hp tractor will pul a 8ft tandem disc in all the above conditions.

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03-02-2012 16:42:59

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 Re: HP vs. Harrow Size in reply to Farmallb, 03-02-2012 15:38:27  
A Model C Allis Chalmers is about 22 hp. No way it will pull an eight foot TANDEM disc. Other stuff you said is right- many variables, soil type, flat, hills, etc. Older discs, not much of an issue with design, but later ones, like JD cone blades...turn more dirt but take even more power and traction. JD 210 with cone blades, 14 feet, 3020 craps out on the level, dualed 4020 snorts in plowed ground. Disking cornstalks doesn"t take much power. Cutting plowed dirt does.

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03-03-2012 07:06:48

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 Re: HP vs. Harrow Size in reply to JMS/.MN, 03-02-2012 16:42:59  
Depends on the soil. Here on flat plowed ground we used 7 and 8 foot tandem disks with a spring harrow behind, using AC B or C tractors. Some fields we had to use either just the spring harrow, or get out the D15 with the snap coupler disk.

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03-03-2012 20:12:56

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 Re: HP vs. Harrow Size in reply to Jg20601, 03-03-2012 07:06:48  
7 or 8 foot (tandem?) behind a B or C had to be a little roller, didn"t cut anything, even in first gear.

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