Can't agree more SB47. The very though to split I refer to as the "uglies". They get thrown on top of the stacks and people can take them for free as a bonus. No one ever turns them down.
I read through the manual of my Yardmax 25 ton and I didn't see where it mentioned anything about which wood for the 4 way.
I've used it in smaller oak rounds without any problems. I probably not gonna try it in big knotty rounds, I'm broke and cheap and I want my splitter to last a long time.
....Just like trucks, they have load and tow ratings that if exceeded could result in damage. Drive it hard and it will wear out much faster.
c5rulz, I like mine. Hard to see the scale here but the pusher plate is about 12" square. The single wedge about the 4 way wing is about 28" high, the wings are about 12" each. The red part of my tble is about 36" wide x 72" long. Splitter throat is 38" long.
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I like that iron and Oak Splitter you have there. I looked for one but could not find one so I end up getting an ALLWOOD splitter.