April/May 1997
A Simple Way to Calibrate
Your Grain Drill
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Prairie Grains is the
official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain
Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.
The Ramstad Brothers of Ada calibrate seed with a device that hooks on the drill frame behind the press wheels. Via pulleys a small motor turns a shaft-mounted boat trailer roller that rotates the press wheels until the proper number of revolutions have been made for the calibration check.
Gordon Ramstad, who farms with his brother Glenn near Ada, MN, says the device they use to calibrate their grain drill is no big deal. "This simple machine just makes it easier for us in the way we like to do calibration," he says.
That's the beauty of it.
University of Minnesota Small Grains Specialist Jochum Wiersma stresses the need for proper drill calibration, as seed size and weight of wheat varieties will differ compared to the standardized "one size fits all" seeding rate tables found in your operator's manual or on the inside of the seed hopper lid. Here's how the Ramstad brothers do it, in Gordon's own words:
"Our seeding rates for wheat vary depending on the seed count per pound for the seed we plant. Recommended seeding rates for wheat are 1.2 to 1.5 million seeds per acre. Clean seed varies widely in seed count per pound, so the only way to be sure of a drill's seeding rate is to (1) do a seed count per pound for each lot to be planted to determine the seeding rate and (2) check the drill's calibration with the seed to be used.
This calibration is done in the yard for each seed lot using a simple machine built several years ago. This machine, an electric motor turning a rubber wheel that, held against the drill's press wheels, turns the feed rolls.
By turning the press wheels a certain number of times, the distance, thus the area is known. Weighing the seed dropped by the feed rolls gives the amount seeded, so knowing area and weight, the pounds per acre at a certain drill setting is determined.
Our drill has an end transport so it is convenient to put a tarp or piece of cardboard under a section to collect the seed. For a 10-foot section of our drill, the press wheels need to be turned about 610 revolutions to equal one acre. We usually run only 1/4 to 1/2 an acre but that's still 152 or 305 revolutions, a lot of turning by hand! That's the reason for having the machine to do the turning, so all we do is mark a spot on the press wheels and count with a counter until the proper number of revolutions have been made for the calibration check.
The machine we use is a 1/4 HP 1725 RPM electric motor that turns a shaft on which is mounted a boat trailer roller. Pulleys are sized so that the press wheels turn at about the same speed as when working in the field - about 6-7 mph. (Our 1725 RPM motor has a 2-3/8" pulley turning a 3-1/2" pulley with a 1-5/8" boat trailer roller on it, which turns the press wheels about 6 mph - any combination giving an approximate seeding speed will do.)
Our machine hooks on the frame of the drill behind the press wheels. A bar stuck in one of the tubes forming the carrying handle creates enough leverage to hold the rubber wheel against the press wheel without slipping. A switch on the motor is handier for starting and stopping, but just plugging in and unplugging works too.
To find how many revolutions your drill's press wheels have to make to cover an acre, measure the diameter of the press wheels in inches. Divide by 12 to get the diameter in feet. Multiply that diameter in feet by 3.14 to get the distance the press wheels travel in one revolution. Multiply that distance which is in feet by the width of the section or portion of section to be used for calibration in feet to get the area in square feet your drill covers in one revolution of it's press wheels. Divide that area in square feet into 43,560 to get the number of revolutions needed for one acre. Reduce this number by 5-6% to allow for slippage and reduction of diameter due to soft ground.
Example:
1) 26" diameter press wheel/12 = 2.17 ft.
2) 2.17 ft x 3.14 = 6.8 ft/revolution
3) 6.8 ft x 10 ft section = 68 square feet per revolution
4) 43,560 square feet per acre/68 = 640 revolutions
5) 640 x 0.95 (5% slippage) = 608 revolutions
This method of calibration takes a little time in the yard, but can be done before fields are ready to work. It's pretty simple yet accurate, and it's a better feeling knowing the equipment is seeding at the rate we want.
This certainly is not a new idea using newfound knowledge. It's a method that others probably are using that works for us. The same machine is used to turn the drive wheels on our row crop planter to check seed and insecticide rates. Another benefit is being able to observe the drill or planter working, watching (and lubricating) chains and bearings at work, and listening for unusual noises while the unit is in the yard or shop. Cost is very low for the machine that does the turning and the method is adaptable to any seeding or planting unit where the drive wheels can be turned and the seed collected."