Jim,
I think part of the controversy surrounding box blades on this board stems from what we are each trying to do with them. This post reflects my own experience, observations, and conclusions, right or wrong. I’m sure they conflict with other’s.
If you have hard packed dirt to move, you need the box blade to act as a true cutting instrument. If spreading gravel or fluffy dirt is the task, a box blade acting merely as a pushing/smearing device is adequate.
For true cutting, the fixed front blade/fixed rear blade style of box blade is an awkward compromise unless you are willing to manually or hydraulically adjust the top link with each reversal of direction. Either way, you need to get the leading blade much lower than the following blade. My former box blade with 2 fixed blades, when leveled from front to back, had the front blade slightly lower than the rear blade. That seemed right since most use is forward and the front blade will dominate the rear. Going forward in hard clay, the front blade would penetrate and cut aggressively for a short distance until the rear blade started dragging. At that point, the box blade just skated along without picking up much more dirt. In reverse it was worse. The rear blade being higher, never had a chance to penetrate. Instead, the lower, front blade dragged and smeared, leaving the higher, rear blade to only push loose stuff. Eventually the box blade would slide up out of the bite. I had no hydraulic top link to get the secondary blade out of the way and manual adjustment was impractical.
The other disadvantage to double fixed blades is the dead volume between the blades. When that volume packs with dirt, pushing and smearing is about all you can do since the cutter clearance is gone. Its not obvious what is happening unless you get down on your hands and knees. Its tough to scrape that dirt out since 2 sets of blade retaining bolts protrude into that dead volume. I think this is a problem with or without top link adjustment.
A roll-over blade addresses these issues by only having one (double edged) blade. It can be rolled over to provide a single blade oriented to cut in the opposite direction. No tag-along secondary blade to interfere with the primary blade. No dead volume between two blades to clog up. A bonus is an intermediate position for “scarfiers only” operation. Expensive and you still have to throw a lever with each reversal of direction unless you buy an even more expensive hydraulically actuated lever.
The option I ended up with is the fixed front blade/hinged rear blade. The way it seems to work is going forward, the front blade is low and the rear blade hinges up as required to keep from interfering with the front blade penetration. Going backward, the hinged blade bottoms out at a lower level than the front blade so that the front blade does not interfere with the rear blade penetration. Also there is no rigid dead volume between the blades to pack up with dirt. And, all this happens automatically when reversing direction-no operator effort required.
I'm not up to speed yet with this hinged blade but my first impression with finish grading is that it penetrates in reverse so well that you can easily take off more than necessary. That’s quite a contrast from my old blade/technique and will take some getting used to. Its also heavier, on a different tractor, and there is a hydraulic top link too. At this point I can't say for sure why its better than the old one, only this it is definitely much better.
John
