dpb wrote:

The work in the straight-knife version is accomplished in three peaks
with essentially no work in between. In the spiral head multiple knife
head, there are 72 (otomh, roughly right, anyway) knives in 4 or 5 (that
I don't remember) spiral rows. Consequently, there are instead of three
impacts to do the total same amount of work instead of just three, the
actual peak work at an instant is reduced and averaged over more,
smaller-effort-each, work intervals. On at least the Byrd heads, the
cutter faces are also angled slightly instead of being parallel to the
face so that they tend to have a shearing cut that, similar to skewing a
plane reduces the effort as well as helping to reduce tearout on
difficult wood.

Yes, this is what I was thinking as well. Only issue I'd have is if
both machines remove the same amount of wood over the same time interval
(feed rate) then both are doing the same amount of work. The segmented
cutters do a little work all the time, the 3 blade set up does a lot of
work some of the time. Your point on angled cut is good as well. I
don't get how the segmented cutters could require more HP though? The
Griz I was thinking about is only 3HP, so that could be an issue.

--
Jack
Please don't tell Obama what comes after a Trillion!
http://jbstein.com