 |
 |
|
Basic
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 into: How Big, How Fast, How Powerful is it? So we'll begin with these three questions, although as you learn more you'll realize that they are not as important as they may first seem.
"We only hear what we understand" Goethe "We only see what we recognize" ?
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.
(i.e. in
"Talk sense to a fool and he calls you foolish" Euripides