It looks good at first but consider this:
Most machines don't have flat bottoms so to prevent the casting edges,
from going between and binding-up the balls, you'll have to add a 2X4
(the width of the ball plate) under the machine to roll on the plates;
a pretty good lift with a pinch bar.

If you want to lift higher with a pinch bar you lift the machine as
much as you can first and, while holding the machine up, slip a block
under the machine, across the full width of the machine (easier with a
helper). Then reposition your pinch bar on a block the same thickness
you've put under the machine and lift the machine again. You've just
lifted twice as far as you could previously.

If you intend to lift the machine more than say 2 inches (for example
to use thicker roller skates) you should go to the opposite end of the
machine and, if you've set the first end of the machine solidly on
2X4s, raise this other end up to the level of 2-2X4s and blok it; then
you move back to the original side and raise that up to 3-2X4s, etc.
etc. until you get to the height you need to go. It's fast and easy,
just have lots of short pieces of 2X4 and maybe a helper. And watch
where everyone's fingers are, and let everyone know that pinch bars CAN
and DO slip.

That said, to use those plates you should have three to a side to keep
the machine perfectly stable (some machines you could get away with
four) and my handy calculator pen tells me that comes to $93.12 plus
shipping (and maybe tax ?). Why not just use 1/2" rollers ( get three)
a few inches wider than your machine (you want them wider so you can
slide the machine sidways on the rollers when you turn or position.
You can put 1xs or plywood down to protect the floor. A lot faster and
cheaper than any other way to move machines short distances as you
discribe (many times I would have killed for a level floor...Mr.
Lucky). Just watch the fingers.

dennis
in nca