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QUESTION:I need to make a thumb for the 580CK Case tractor backhoe.
The bucket on the front of the machine will keep the same angle as it
is raised and lowered. So, for example, if the operator tilts the
bucket to a ten degree angle with one lever it will keep that angle as
the bucket is raised or lowered with the other lever. I want to plumb
the thumb to work the same way. It appears to me that it may be
valving that makes the front bucket behave this way. Anybody know how
this is done?
ANSWER: On my back hoe (JD500C) the loader bucket leveling is a function of the
mechanical linkages / pivot points. It is parallelogram configuration
with four pivot points. One leg of the rectangle is the bucket tilt
cylinders so the length varies tilting the bucket. As the lift cylinders
push the main loader booms up that parallelogram adjusts keeping the
same angle.
Another setup I've seen that is hydraulically based does not use valving
per-se, but uses a sort of a "servo" cylinder that is mounted at the
base of the pivot and by being appropriatly sized will "trim" a front
cylinder that is the tilt control for the "front end". It works pretty
much the same as the setup on my backhoe, but replaces one physical
linkage with a hydraulic one. I've seen this setup used on tele-handlers
mostly. Possibly your 580CK uses something similar. I would think that
they would avoid using a true valving setup since the complexity would
be rather high.
The backhoe thumbs I've seen don't appear to do any sort of angle
sensetive control. I've seen fixed thumbs where the bucket cylinder does
all the work, and active ones that use a seperate control. In both cases
it does not appear that there would be a need for angle sensativity
since whatever you are holding is pinned between the bucket and the
thumb, neither of which will move relative to each other as the boom and
or crowd functions are operated.
The factory service manuals will tell you a lot. That's one of the first
things I got for my backhoe and the set was <$100.
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