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I have a wood cutting saw that I mostly use to cut up scrap lumber for
my wood stoves. Mine is just a 10 inch blade and powered by a 1.5 hp
motor. The blade turns at about 4000 rpm. Works good, but not really
safe.

I would definately drive an 18 inch blade much slower. The 4000 rpm is
somewhat dictated by wanting a small pulley on the saw blade mandrel so
I can cut 4 by 4's. The saw blade that I have has a fairly thin kerf.
An 18 inch blade would probably have a kerf two or three times as wide,
and therefore would require two or three times the hp for the same
cutting speed. My intuitive guess is that hp required is proportional
to the surface area of the sawdust created per minute. I think you
would be happy with a three hp motor. I would rather stall the motor
when the blade binds that have so much hp that it never stalls. And
instead throws wood at the operator.


I think you are right - if a 10" blade normally operates at a given cutting
speed at say, 3600 RPM, an 18" for a similar cutting speed would be about
2000 RPM. This seems quite reasonable as I have noted that *max* speed
advertised for the particular 18" blade I was looking at is 3600 RPM. The
HP being proportional to the rate of chip production also seems reasonable
so, particularly if the saw is not forced too hard, 3 HP seems like it would
do it alright. As well, the logs I will be cutting are all aspen & balsam
poplar which, as woods go, are quite soft (and, it's all cross cutting, no
ripping).

As far as throwing wood, I am thinking of devising a long actuator "handle"
which would be operated from the side of the saw rather than in front of it.
I think that would be safer but would appreciate any comments otherwise. It
also seems to me that operating the saw as a "chop" saw (pivoting feed as
opposed to sliding) would also tend to make it safer as the blade would not
tend to pull itself into the wood.

Laurie Forbes