Advanced Questions
What about hydraulics? They are a wonderful invention transmitting power (piston or motor) anywhere you can run a hose. David's "Scissor Lift" couldn't work without them. The large hydraulic sawmills are interesting to watch, logs lifted, loaded, clamped, cut and turned by an operator sitting in a lawnchair under an umbrella with a beer, pushing buttons. Of course you'll still need to get the logs to the mill and you'll need at least one other person to remove the boards. If you're running a large commercial operation, then this is the only way to go. But, for a small one man hobby operation, they are impractical. The cost of the hydraulics alone (pump, spool valves, cylinders, motors and hoses) could be more than the whole rest of the mill. Hydraulics take power and require a larger engine, therefore bigger, heavier (expensive) mill, etc....
What is the difference between "I" and "C" frame power heads?
Just as the letters look, an "I" frame is a straight "bar" with the
bandwheels at either end. A "C" frame is like the traditional shop
band saws with the bandwheels at the ends of the "C", to give a larger "throat"
and a greater cutting depth, necessary for shop use but requiring a stronger
heavier frame as a "C" frame is weaker by design. Not being engineers,
sawmill builders took the shop bandsaw design (that they knew) and turned it on
its side. This is unnecessary in a sawmill. You don't need this
"deep throat" to cut boards from the top down. Their mills could actually
cut the bottom of the log in the first cut which would be ridiculous, of
course. This unnecessary "ability" comes at a cost, and the powerhead must
be bigger and heavier, etc..
When David designed his first "I" frame
in the Model I, all the major sawmill manufacturers were using the cumbersome
"C" frame design. Since his first website showed the Model I in the mid
'90's some manufacturers have started using the "I" frame design in their
mills too.
What about purchasing blades? Most sawmill manufacturers supply blades for their mills and you buy from them. With Mr. Sawmill, David gives you the blade specs. and the name of a blade supplier near you, so that you can buy direct. By setting up an account or with a credit card you just call the supplier and the blades will be shipped to your door in a few days.
What is the optimum blade speed? The best blade speed,
measured in feet per minute or fpm depends on a number of factors including
the type and thickness of the wood, whether it's frozen, motor horsepower,
etc... More speed requires more power but too much speed can cause excess
friction and bandwheel vibration. Too little speed takes too long to cut
through the log and you could be wasting power. With a 13 hp
motor, 19" bandwheels and a 4 1/2" motor pulley at 3600 rpm the blade speed
will be 4265 fpm, a good compromise.
Since Mr. Sawmill is so efficient
(the motor directly drives the bandwheel) we use a 4 3/4" pulley (i.e.
centrifugal clutch) for a blade speed of 4,500 fpm with excellent results.
Do I Need A Centrifugal Clutch? The industrial
centrifugal clutch that we use costs $300 and a simple pulley costs about
$20. If you want the blade to be stopped with the motor idling then you
must either use a centrifugal clutch or design a motor engagement system where
the motor (or an idler pulley) moves to loosen and tighten the drive
belt. This puts more wear on the drive belt as it slips during engagement.
It is possible to use just a fixed motor and pulley (the
simplest design) but the blade will be turning all the time. Some may
consider this more dangerous, turning and clamping a log beside a running
blade but it's not as bad as it sounds. The blade is moving slowly, only a
small part is exposed and with shorter logs you can be more than six feet
away. It's still far safer than any chain saw.
You could try that out
and see how safe you feel with it, knowing that it's a simple job to change to a
centrifugal clutch later. Since most motors are so easy to start (one
pull) you could just turn them off. You'll be starting the motor with the
blade engaged but it's not that difficult. You will put more wear on your
pull start mechanism though.
