Basic Frequently Asked Questions
Like most people just learning and not being familiar with a machine we only ask questions about what we can relate to and think important. That usually translates to: How Big, How Fast, How Powerful is it? So we begin with these three questions, although as you learn more you'll realize that they are not as important as they may first seem.
BIG - What is the best bed length and width?
The best size portable sawmill to use is the smallest
one, which is also the cheapest to build. On manual mills you
must reach over the bed to adjust stops, rotate and clamp the
log, etc.. The narrower the bed, the easier this is to
do.
The same rule applies to length. The shorter, the lighter, the
cheaper to build, the easier to move about, to transport with less
bottoming on rough terrain and to park, store or cover. And cutting
shorter logs is also easier and less wasteful. A shorter (lighter)
log is easier to transport, load and rotate on the mill. A longer log has
more chance of a bend and there is a greater difference between the top and the
butt end so more wood must be cut off to get that straight beam (cant)
in the middle.
So a good size sawmill to use would be about 16
inches wide and 8 feet long. Right away, you can see a problem
with this. What if I have a wider log or need longer
boards?
This type of problem is constantly faced by all designers
and engineers. You want the biggest, fastest and strongest to take up
the smallest space, use less fuel and be lightweight and inexpensive. (the
most Bang for the least Buck)
Mr. Sawmill has been designed with this in
mind. For its weight and size it can cut a wider and longer log than other
similar mills. The carriage will handle a 30" wide log and the plans show
an 18 foot bed frame with track extensions which will allow an 18 foot log to be
cut. Of course you could make the bed even longer, up to 24
feet*, but then you should use the Palladian Truss or
use 2X6 box tubing. This will add to the cost, weight and cumbersomeness of
course. Another way is to build a detachable bed extension for those rare
times when a longer log is required. Keep in mind that the lumber for most
building projects (including 30+ foot trusses) needs to be no longer than 12
feet.
FAST - How many board feet per hour? A board
foot is the amount of wood in a piece that is 1 inch thick and 12 inches
square. If it's 2 inches thick it would be 6X12 inches, and so
on.
Because it's important in industry, "board feet per
hour" is mentioned by some portable sawmill manufacturers. But
regarding a small portable sawmill for personal use, it's
ambiguous. How much wood you can cut depends on many factors
including the type of wood you are cutting and whether you're working alone
or how many are helping you load the logs and removing and stacking
the lumber and your physical condition, how many breaks do you need every
hour, etc..
If they are referring to how much wood the
sawmill itself can cut, then the logs must be supplied and the lumber removed
instantly. To measure this you would load a log onto the mill and set
it up for the first cut, then start your stopwatch. Cut the log up with a
good helper removing the boards then stop the watch after the last cut.
Divide that time into an hour, then multiply that number by the board feet that
you just cut. That's what your mill can do, but not what you'll be able to
do and certainly not working by yourself.
In a short competition,
because of its efficiency and each using one operator, Mr. Sawmill
can compete with (and even outperform) other hydraulic mills costing
over $20,000.
POWERFUL - What Engine should I use? If
you're building your own sawmill you may wish to use an engine that you already
have. Mr. Sawmill is designed to use horizontal shaft engines from 8 to 16
hp but we find that the 13 hp gives the greatest economy to power ratio.
The 8 hp was slow and unsuitable for the larger logs. The 16
hp cut a bit faster than the 13 but it used more fuel
and cost twice as much. Larger than that is even more impractical on
this mill because you must lift up that extra weight with a hand crank and the
cost of the motor is many times more. The bigger motors also require
two drive belts and Mr. Sawmill only uses one, as it also drives the
bandwheel. The carriage would also have to be redesigned to
accommodate the extra size. Remember, as the power increases a
bit, the fuel consumption increases a lot.
In a one man
contest, Mr. Sawmill cut the same amount of wood in less
time than a 20 hp hydraulic $20,000 mill, and we used 3
litres of fuel to their 10 litres. That was possible because their
hydraulics took some of their horsepower and although they went through the
log a bit faster, we returned our (lighter) carriage much faster. We
also moved our powerhead up and down more quickly (and accurately) and
clamped and unclamped the logs faster. (We could have handled
a larger log than theirs too.)
Cutting through a log a
little bit faster takes quite a bit more power and for each cut
the carriage must be returned to start the next cut. Therefore the speed
of the return is just as important as the speed of the cut.
Electric or Manual Start? An electric start is great
if you're not near the engine when it must be started, or if the engine is
difficult to start. Most modern motors (including the
Chinese clones) start very easily, with the first pull if the choke's in
the right position. Because you're always beside the engine when you
start it, the electric start is unnecessary.
Also, the electric start
clones are about $40 - $60 more and 4 pounds heavier and you must also
purchase a battery then build a battery box. If the battery is mounted on
the powerhead the cables can be short and they don't need to move, but you will
be cranking up this extra weight. The lighter motorcycle and lawnmower
batteries are also more expensive than the heavier (and more powerful) utility
batteries. If the battery is mounted on the carriage then you're not
lifting it up but now the cables must be longer and move with
the powerhead, clearing everything.
So, for a small portable
mill, an electric start is heavier, more expensive and more
trouble.
* Box
Tubing (H.S.S. for Hollow Structural Steel) is usually shipped in 24 foot
lengths.
Angle Iron, Flat and Round Bar typically come in 20 foot
lengths. (in Ontario,
Canada)
