The top link anchor point and length is important when the implement is lifted too!

If the top link is too short, the angle of "attack" of the machine changes more dramatically when lifted or lowered.

If the top link anchor point is too low, the implement tends to kick up in the back as it's raised and down in the back as it's lowered.

too high and it droops in the back when raised and kicks up in the back when lowered.

As you say you can set the length for an ideal operating position, but any deviation from that requires adjustment if the geometry isn't close to right.

If you intend to use a PTO the design options become pretty limited.

Foster, before I even started any steel work, I used a sheet of plywood with cut-out cardboard mockups of the arms and top link pinned to it with small nails to get an idea of the pivot geometry. The final design isn't perfect, but within the working depth range of most implements, the angle is fairly consistant.

The subframe that all the hitch components are attached to (see photo of it under Old Magnet's first post) is welded to the stock Cat swinging drawbar assembly, which bolts up to the tractor rear with two cast steel brackets. I incorporated an additional strengthening downtube of 2x4 tubing which bolts to the topmost pair of holes of the drawbar mount and is welded to a point near the top link mount. I took some photos of the Cat this morning, including one that partially shows this downtube and its bolts.

G'luck on your own project. - Richard

I don't follow your logic there. Parallel is parallel, doesn't matter what the vertical difference is but if the pivot points are offset and the top link is shorter, the reduced arc length will give you the tilt you describe. Also may work for tillage implements but will drive you nuts trying to grade with box scraper or terracing blade.

Maybe this is what your describing:
If the tractor attachments points are closer together (vertically) then the implement attachment points then the top link would be longer than the bottom links (when implement is vertical) and you would have a reverse arc action as compared to the shorter top link.

Catspotter

Thanks for posting up the pictures, they are great.

I looked at a lot of wheel tractors in the weekend, most of the "latest crop" of machines with a hitch of category 2 and bigger have the top link anchor about 8 to 10 inches aft of the bottom ones, which is pretty much what I take from Neils comments. Funnily enough. some of the bigger versions of implements that need good angle control (eg back blades) now have trailing wheels.

Cheers - Foster

I think works to lift the rear of the implement more by lowering the tractor attachment point of the top link. This is not parallel. That way the rear pin of the top link is arcing forward faster than the draft links as the implement is raised. This would be offset somewhat by a longer link length if the implement was adjusted parallel to the ground when lowered.

Some tractors have several pin positions for the top link to allow some adjustment and also for CAT 1 and 2 or 2 and 3 depending on the size tractor.