Platform Mechanics

August 26, 2011 09:08 PM
Platform Mechanics

Precise adjustments and patience with groundspeed provide optimum performance from soybean platforms

In a perfect world, farmers would harvest soybeans at 6 mph, lose less than 1% of total yield to reel and cutterbar shattering and leave the harvested field as smooth as a pool table. In the real world, two out of three isn’t bad.

Harvesting test plots and seed fields for Stine Seed Farm, Adel, Iowa, exposes Steve Luther, assistant farm manager, to soybean varieties and traits up to five years ahead of their release to farmers.

He says the next generation of soybeans will favor farmers who pay attention to properly adjusting and operating soybean platforms.

Groundspeed and its relationship to efficient cutting is critical. After experimenting with groundspeeds, Luther set a speed limit of 4.5 mph for Stine’s combines during soybean harvest.

"Our combines will easily handle more than 4.5 mph, but at more than that you’re going faster than the sickle can efficiently cut the stems," Luther says. "You can see it if you bump the hydro handle forward—you start to see more shatter loss on the cutterbar, the cuts on the stems are more ragged and the fields don’t look as smooth when you’re finished."

Leaving harvested fields as smooth as a pool table requires careful adjustments and acknowledgment of some mechanical facts of life about soybean platforms.

"There’s a mechanical limit to how close a cutterbar can cut beans," says Jeff Gray, senior product specialist with Claas Lexion. "Most cutterbars and skid shoe assemblies are at least 1½" thick, so to cut closer than 2" is pretty tough."

Moderate pressure. Gray says many operators try to use extra down pressure to force soybean platforms to cut closer. Excess down pressure decreases the "flex" range of cutterbars and makes them more prone to push dirt under damp conditions and collect rocks when it’s dry.

Luther recommends keeping cutterbar down pressure moderate. "We keep down pressure in the middle of its range, so the indicator in the cab is actively moving up and down. If you mash the cutterbar into the ground, it bridges across low spots instead of flexing down into them," he says.
Cutterbar angle is critical for a close cut. Luther and his crew adjust their cutterbars to at least a 2° downward tilt.

"We’ve gone a little steeper, maybe as far as 5°, but you really risk picking up rocks when you’ve got the cutterbar that aggressive," he says. "At 2° to 3°, it seems to give the best cut.""

Some operators assume that the faster the sickle moves back and forth, the better it cuts. Not true, Gray says.

"There’s a point where the sickle is going back and forth so fast it inhibits optimum cutting," he says. "It’s moving so fast it cuts the stems at the tips of the sickle sections rather than back in the deep part of the ‘V.’"

Cutting at the tips of sickle sections reduces cutting efficiency. If you’ve cut paper with just the tips of scissors, you’ve felt how it takes extra effort to get crisp cuts. Scissors also demonstrate the importance of replacing dull knife guards. Just as scissors require two sharp edges, close cutting with a bean platform requires knife guards with crisp edges.

"We replace knife guards on each bean platform once a year, so the sickles always have sharp edges on the guards to shear against," Luther says. "We have two sickles for each bean platform. During the peak of the season, we swap and rebuild sickles at least once a week. With tough-stemmed varieties of beans, we may switch every three days."

Reel settings also contribute to shatter loss. Gray likes reels to spin roughly 1 mph faster than groundspeed to gently flip the crop into the cross auger. He says that reels "tell" operators if they need to adjust their speed or position.

"If it’s bunch feeding, with big clumps building up on the cutterbar, the reel is probably too high or is turning too slow," Gray says. "If stems are riding and wrapping around the reel, the reel speed is too fast. If beans are bouncing off the cab windshield, either the reel is too low, the reel speed is too fast, or both."


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