I have a 4 x 24 cylinder I bought from ASC and a homemade ram. I toyed around with the cutter and through 4 iterations I got what I want: The blade 8" tall, is as sharp as my hand grinder can make it, and is made from 3/8" steel stock. Approximately 3 inches beyond the point and welded to it, is the wedge which flares about 20 degrees in both directions. This setup provides the maximum #/square inch initially to get the blade into the wood and once it's started the flare to force the log apart.
I had been running it with my tractor but to offset cabin fever this winter I had an old riding lawn mower sitting around with a shot deck and decided to make a pump driver out of it hoping to be more convenient than the tractor and it surely turned out that way.
The engine is a 15 hp Kohler 1:1 V belt driving the 16 gpm 2 stage pump (8 hp drive requirement @ 3600 rpm stated) from Northern Tool where I also purchased the "log splitter" control valve, Lovejoy drive sockets and mounting bracket for the pump, all to allow me to V belt drive the pump. In surfing the www I found a hydraulic site where I learned a few things about log splitter hydraulics which helped in the design.
First thing I learned was to keep the runs short. Outlet of the pump is 1/2" so the pressure line to the controller is 1/2" and about 18" long. Return from the pump is 3/4", about 24" and routes to the filter and 2.8 gallon oil reservoir. Also the site said that making the return large helps your cylinder retraction time. Lines to the cylinder from the control are 1/2" x 5' each, reason being I wanted to sit between the splitter and the drive unit. Unloaded cycle time is 7 sec out and 6 back with the Kohler running at the notch in the throttle plate which should be right at 3600 rpm. I am really pleased with that as my tractor was really slow....partly because I had very long 1/2" lines between it and the cylinder, plus the pump was only about 8 gpm.
Yesterday I was splitting some 24" trunks from a tree I cut back in December; wood is Hackberry, kind of green and stringy like Water Elm. I deliberately made my splitter close to the ground so I could roll logs to it and minimize my lifting, in addition to being able to work large pieces alone, as I was doing yesterday. On these big guys, I used automotive ramps to roll them up and onto the beam. I could hold them in place with one hand and reach over to the mower to get to the control handle for the split.
The ram zips right up to the log at a nice clip as stated and as soon as the blade contacts the log the second stage of the pump immediately kicks in. You can hear the engine load up somewhat with the new load but the second stage (high pressure, slow speed) only runs for a couple of seconds, just long enough to get the knife edge embedded in the log and then the pump reverts back to low pressure high speed, and the ram moves out again and pushes the split log off the end.
In running the numbers it says that my setup is capable of only 15T of force. But the name of the game isn't force per se, it's force per unit area. That's why I have the sharp edge on the blade and keep the wedge part back from the tip giving time for the blade to get embedded in the wood before you attempt to split it.
It's a pain, but if you are really interested I can send you some pics of my setup.
HTH,
Mark