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Getting broken pieces of cob in the sample. My questions are,

1. Is it possible to thresh corn gentle enough to get almost 100% whole cobs out the back with a conventional machine?

2. If so, does the rear of the concave need to be opened up? The owners manual says nothing about the rear, only how many turns to open up the front.

3. I do not have any concave block-off plates installed. Is that a must-have piece of equipment?

4. I am using a non adjustible air foil top screen (some call it a round hole screen) standard bottom screen, 1000 RPM fan speed, rasp bar cylinder. Is this common with an air-foil top screen?

I am very familiar with adjusting a combine, but had a few specific questions about corn. This is a relatively new crop for me, mostly rice, soybeans, and wheat down here.
 

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One rule of thumb we always used on any conventional combine is go find an average thrashed cob. Then open your rear inspection window to your concave. Make sure that cob can fit in between the concave and rasp bar on the BACK side of the concave. Then check the front and open it 1/4" to 1/2" more than the back depending on moisture. Should only need to run cylinder between 300 to 400 rpm's if the corn is under 18%. Airfoil is awesome in wheat and small grains, but not my first choice in corn. You will get more broken cobs stuck in it and through it. But still should do a good job. I found the the problem I had the most is not with cobs, but with stems getting stuck down in it.
 
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