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post #10 of (permalink) Old 11-28-2017, 02:10 PM
Transaxial
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Join Date: Jun 2012
Location: east central Alberta
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Originally Posted by chance2 View Post
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This is the 23 bar I have in the 8820 now. I built this one from scratch. No actual pictures of the finished product that survived the great phone crash of 2013. I built this one on a 22.5 inch diameter as soybeans were starting to move into the area and if I had built it on the 22.125 inch diameter, it probably would be cracking a lot of beans. I don't think the increase in threshing diameter necessarily hurts it's performance in wheat. The bars are .250 thickness instead of .375 thickness. (The drawing does not really convey the bar thickness as well as looking at the finished concave.)

Deere use to build 2 concaves for it's conventional lineup. A grain concave built on a 22.25ish inch diameter and a corn concave built on about a 24 inch diameter.

Trying to use a corn concave for threshing wheat just does not work well as the concave it too tight in the center of the concave and start to open up toward the back of the concave so the back section can not effectively separate wheat and other small grains.

Likewise a small grain concave does not work in corn as the concave has to allow stover onto the walkers without shattering the cob and overloading the chaffer while maintaining a steady narrowing of the gap down to the diameter of a cleaned off ear. Trying to open up the back of the concave to the diameter of a cleaned off cob and opening the front to allow a full ear into the concave leaves a wider space in the center of the concave and material really only threshes and separates on the back half of the concave. Either situation really diminishes combine capacity in the other crops.

The test concave for the 8820 was an older Sunnybrook that I welded key stock above the wires, and between the webs. It ended up being a 21 bar. It worked well. My original R&D concave was a 17 bar in a 7721. Much easier to change the concave on the 7721. In barley the 7721 had better capacity that a 9600.

Setting the machine is a bit different as the separation starts right at the front of the concave instead of 1/3 the way back with a filler plate concave and the increased number of bars holds the material a bit longer in the concave. Cylinder speed is somewhat reduced as the crop mat is held up by the bars and receives more strikes before it can disappear below the bars and out the bottom. In wheat I usually start with the front of the concave around 1/2" open and the rear somewhere around 3/16". Cylinder speed rarely exceeds 825 RPM unless the wheat us really tough.

Being more aggressive can really overload the shoe in a hurry, so you have to watch your adjustments throughout the day as crop conditions change. Something as brittle as bone dry canola can still be threshed without overloading the shoe, it just takes some careful adjustment. (Yes we drop canola stalks occasionally.)

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In green stalk straight cut canola it really works well as you have to put a lot more threshing speed to the cylinder to get those pod shatter resistant pods to crack open.

If I were to build another, I would more that likely go to the 21 bar.

The sample the machine makes is really nice compared to when I started with the old beast. The air foil chaffer takes some getting use to especially in canola as I have to open the sieve up to about 5/8 inch or better to bet enough air on the airfoil to make a really clean sample.

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I don't think Sunnybrook makes the staggered 8 bar cylinder any more either. They can be found at combine wreckers for a pretty reasonable price though. It really gives the machine an apatite. Getting the machine to thresh and separate everything the first time at the concave gives it capacity like Deere engineers could have only imagined.
Great post chance! And great work on designing and modifying the all important threshing system on your combine! And looks like you have your own touch on a few other areas too. This is a really good understanding and description of how a cylinder and concave need to work to properly do their job in the vastly different crops these machines are sold to harvest. I really believe most combines are not set up properly to work at their best potential and it is refreshing to see your approach and then to follow up and actually build a properly designed wheat concave. Good for you!! Some of the problem with anyone selling a concave is that most buyers do not totally understand what they really need and would not accept that two different concaves would be ideal. So making one concave that suits your needs like threshing wheat as the biggest challenge, and then accepting a decent compromise on the easier to thresh crops seems like a pretty good fit. You have some very good engineering detail in your design. Is your design better than the many aftermarket concaves out there? Your logic seems in line with what I have found which is to thresh all the grain the first time through and maximize separation before it leaves the concave. As soon as a kernel of wheat is freed from the head it should have the opportunity to drop to the grain pan. Filler plates stop that. Is there any way that making the concave slightly longer at the front, even 2 or 3 bars, could help without restricting a smooth flow of crop? Like Class intensive threshing segments that bolt in for hard thresh crops and help a concave that was designed for everything to thresh wheat. It is great to see some reliable old machines brought back to life with new parts that makes them work better than when they were new!!

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