Yes I have built one a good 10 years ago, it was added on to a log loader. I am planning to build another soon, this will be stand alone I have a Nissan TD27 diesel from a Airman compressor along with a few other goodies to start with but am going to have to look for many parts to get of the ground The basics will be the Pump, Hyd motor for saw, (the blade sprockets and chain are readily available here)
https://www.baileysonline.com/search.asp?SKW=16H+18HX&catID=177
One question I got lucky the first time with what I stumbled on to use, is the drive motor for the slasher chain lets say for a 72” bar running a ¾” pitch chain how much torque and speed would on shoot for. I have seen log slashers in action and this size bar and chain should go through a 3ft dia log in less time than it takes to count to 5 (a 1 to 3 min chore with a chain saw depending on chain sharpness and the operator) Of course I no longer live in a big logging area so it is not as easy to scarf up parts as it was.
The cylinder is also important if you go to the trouble to make a processor do want to be able crack ANY block that goes into the splitting part of the processor. (multiply cylinder piston dia X 3.14 will give a close area in sq in of piston and multiply that by your pressure you apply cylinder and that gives splitting force) So a 5” cylinder will give about 20 tons with 2500 psi
Once the power supply and hydraulics are in order what remains is to design it all on a frame in a manner that each step of the process flows together in a fashion so the steps help and don’t fight each other. I have bought these plans
Miller's Woodcutting
but I must say, they not much in the way of plans and I am going to make mine VERY loosely based on these but with MANY changes.
What works well for me is break the job this does into steps or phases 1st is the material handling of the logs to processed these process may include parts like lift arms and a conveyor table of sorts. 2nd will be the parting of the log into the desired length block this part may be a simple as pinned chainsaw or as complex as a hydraulically powered and activated “slasher” bar. Next the correct length block would likely gravity drop into a hopper or such where it will be in position to be split into correct size finished product. With the great variation in log diameter usually available for fire wood a 4, 6, 8, or maybe more way splitting head is considered desirable. Of course it would be best to try to affect a design that will give the versatility to have all three.
I don’t think I will be able to get mine built before I need to cut this winter’s wood as I should have already been done, but I would like to get the frame done with motor, pump and splitting section and use it as likely the worlds most overpowered splitter for now and work on the rest of the phases as time and $ allows