Go BottomBox Scraper Use Position Control
 | TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2001-07-15 30092
I hope these comments help somebody who is just starting to play with a scraper. I may have left some false impressions awhile back. I've commented that the blade angle (adjusted by the top-link) on a box scraper is the main thing that determines the cutting/spreading action of a scraper. I've also commented that holding position control, rather than floating the 3ph, can be used to keep the scraper from sinking in soft surfaces but the problem then is that the scraper goes up and down when the front wheels go over hills or dips. My example was that the scraper digs a divot when the front wheels go over a hill. That does happen, but not because the scraper is held down by the hitch (like a loader). That was a misconception that I got rid of myself not that long ago. Position control can prevent a 3ph from floating down, but most 3ph’s always can float up. Never the less, divots are dug. This is what I think happens. When a box first starts up a hill, the ground angle changes with respect to the blade. Until the entire box gets on the new slope, it's equivalent to shortening the top-link, which increases cutting action. In addition, if the 3ph has no float, some of the scraper’s weight is on the 3ph. If the front wheels go over a hill, the 3ph floats upward, which puts all the weight on the box. The additional weight increases the cutting action. However, there is one thing for certain. If a load is being dragged, and little float is used. When the front wheels go into a dip, the box comes up and dumps the load. It's a pain to have to back up and pick up a dumped load, and I always seem to gouge my nice smooth grade doing it. I usually use a lot of float so that doesn't happen. I also usually slightly lengthen the hydraulic top-link and the bottom of hills and then shorten it again after the box starts up the hill so I don't make the hill any longer. I avoid holding position control except during the initial spreading of loose gravel. If a surface is so soft that the box sinks even with an extended top-link, I compact the surface with the loader bucket until it can support the scraper.
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| Stan in Calif
Join Date: Feb 2002 Posts: 47 Sacramento Valley- Glenn County 
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2001-07-19 30238
Good point, Tom. I think it needs to be emphasized that few, if any, of us have true downforce on our 3ph. I've seen it only on larger industrial tractors that have the weight to handle it, as it unloads the rear wheels, reducing traction. The only "downforce" we have is from the weight of the implement and the "self feeding" action of certain implements such as plows and rippers. There is a little bit of this effect with a fixed rear blade box,and a little more with a hinged rear blade.
BTW - to answer another unasked question - draft control doesn't provide downforce - On the contrary, it is "upforce" designed to counter the self feeding action of plows and rippers.
Hyd. top link doesn't provide downforce - It just transfers the implements weight from front to rear, but it's still floating.
Also, I've given up trying to make fine adjustments with the rockshaft lever - it's not precise enough. I use the hyd. top link for this. True, it's changing the angle, but also the elevation. We are all still learning. ....
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| kay
Join Date: Posts: 1
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2001-07-19 30239
Stan
VERY well said! ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-07-20 30249
Yes, Stan: You managed to get my collective experience and then some in far fewer words than I typically use. When I finally figured this stuff out awhile back, I was still stuck with the idea that the scraper did seem to dig holes when the front wheels went up hills. The above post was my think through trying to reconcile how I believe a 3ph works with what was happening. Like you, I find the 3ph pretty useless for adjusting the scraper's action. Most times I just set it for plenty of downward float and never touch it during operation. There is a lag to 3ph movements, and are just not precise enough to be useful. I wondered about the lag in 3ph lift. The other day, I was dozing a shallow excavation with the rear cutter and pushing the dirt into a pile at the back end. The box would float up towards the top of the pile, and then I’d lift the box so I wouldn't drag dirt back into the hole. There was a lot of float as the pile got higher, and I noticed the lag on the 3ph became longer. I suspect that when a 3ph floats upward, enough oil has to be pumped into the cylinder to bring the position up to the where the box is before it starts lifting. If that's the way it works, an operator is unlikely to know how much float is present and therefore how much lag there's going to be. Maybe that's why I almost never touch the 3ph lever when using the scraper. Of course, to think this one through, I'll have to come to grips with the 3ph oil flow diagrams in my repair manual. My eyes glaze every time I look at them. I believe Belarus makes a compact with 3ph down-pressure, but that's the only one I've heard of. I have heard that kits are available. I don't know how they'd work, but I can't see why I'd ever want one. ....
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