Sawmill trouble shooting guide
Jeff Lesak of Jeff's Saw Pounding was knowledgeable enough to put together a troubleshooting guide for circular sawmills. Jeff has since retired and has graciously allowed us to host his troubleshooting guide which you can find below.
If you would like to download a PDF version of this troubleshooter you can download it here.
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1.
BAD COLLARS
How the saw blade is held is one of the most crucial factors that
affect blade performance, and therefore the performance of your mill.
You may have noticed that your saw hammerer often suggests that you
check your collars. Most of
the time, that is where you should look.
Three out of four times, in my experience, bad collars are to blame
for problems with the mill and the blade. How
to check The easiest check for bad collars is to hang the blade on the mandrel, then hand tighten the nut. Set the guides so they are just slightly away from the blade (as you would set them normally). Then tighten the nut with a wrench in the usual manner. Make sure the blade does not move as you do this. If the blade is forced over to one or the other of the guides, you have a problem.
Another check you might try is to use a straight edge.
As before, hang the blade on the mandrel and hand tighten the nut.
Put the straight edge on the blade and see if there is a dish.
(If there is, you may need to get your blade hammered.)
Now, tighten the nut and check for a dish with your straight edge.
If one shows up at this point, you have a problem. Before you decide that your collar is bad, it would be wise to try another check before you go to the trouble and expense of having the collars machined. First, remove the blade. Then rub chalk or a marking crayon all over the machined surface of both collars. With a accurate straight edge, scrap off the markings. If your markings are not removed from the outside 1/8 inch or so of the collar, and no where else, it is worn. And worn in a place that is going to give you trouble. One last thing to check is that the diameter of both collars is exactly the same. What
to do If your collars are bad, there is only one way to cure them. You will have to have them machined. The following diagram will help your machine shop do it right.
There is, however, a fix that might work for you. (This should be considered a temporary thing, however. If your collars need to be machined, you should do that as soon as possible.) Once you have figured out which of the collars is bad, a paper washer, cut from a medium weight sheet of paper (a manila envelope works fine) so that it is about 3/8 of an inch wide and no bigger in diameter than the outside of the collar, can be put on the bad collar. Hold the washer to the collar with a little grease. If both collars are bad, use two washers. If the saw is being dished toward the husk (the teeth forced into the log), put the washer on the fast collar. If the saw is being dished toward the log (the teeth forced out of the log), put the washer on the loose collar. 2. LEAD Next to bad collars, improper lead causes the most problems with the mill. Lead is put into the saw to overcome the tendency of the blade to saw out of a log when slabbing and to give clearance at the back of the saw so that the teeth do not hit so much on the gig (or return). How
to Check One simple way to check the lead is to mark a tooth on the saw. Loosen the guides. Measure the distance between the tooth and the end of the head block. Turn the saw and move the carriage ahead so that the marked tooth is exactly at the same relative position to the same head block and measure again. For a 48 inch saw or smaller, 1/32 of an inch is correct. For a larger saw, 1/16 of an inch is desired. Another way to check is to run a string along the guide track so that the string follows the track exactly. Then, using the same marked tooth, measure the front of the saw to the string. Next, rotate the saw and measure from that tooth (that is now in the back) to the string. This method also gives you an idea how straight your track is. What
to do
Lead is adjusted by moving the saw end of the mandrel slightly.
Some folks call this "sluing the mandrel". Loosen all of
the mandrel bearings from the husk and loosen the belts as well.
You need to do this so that the mandrel is not put in a bend or
bind when you move the saw bearing. Now,
move the bearing block nearest the saw to the left or right as needed to
put in the proper lead. Make
sure the blade is not touching the guides for all this.
Never use the guides to put lead in or out.
When you have the lead that you want, tighten the bearings.
Check the lead one more time to make sure it hasn't moved by
tightening the bearings. How
to Check What
to Do
Take the time to do it right. There
are some things you should not do. Do
not file a lead into the saw. Do
not file the back of the tooth. Do
not use a heavy hit when swaging.
Some people
call them rings, holders or gullets.
No matter what you call them, their job is to hold the teeth in
place, and control and hold the sawdust until the tooth leaves the bottom
of the cut. When the shanks
become worn or damaged, they can not do their job.
And if they are worn a lot, that can cause a dish in the saw ,
affect tension in the saw, and they will not hold the teeth securely. How
to Check
As with the
teeth, take a good look at your shanks.
You can see if they are worn or damaged. You will also need to
check the amount of spring in the shank.
Even an old shank should feel tight when it is put in.
When you change teeth, take note of how much effort it takes to
replace the shank. If it is
going in too easy, the spring may be gone.
To check for wear, use a micrometer to measure the shanks thickness.
If the shanks are more than .015" thinner than a new shank,
it's time to put new shanks in, especially during the winter months.
What to
Do If the shanks are worn thin, replace them. If the corners of the shank are rounded, but the shank is not too thin, square up the edges with a round file. If there is still enough thickness left in the shank, but the spring is gone out of it, you can peen the inside edge of the shank to tighten it up in the socket.
If you need to replace the shanks, try to replace every other one and wait
for some time later to replace the rest.
This will lessen the affect on the tension of the blade. If you are working with an older blade that has some wear in the sockets, it might be necessary to use oversized shanks if standard new shanks do not feel tight enough as you install them. Try to wait as long as possible before going to the oversized shank as they might stretch the socket. A saw that has stretched sockets and will no longer hold the teeth securely is no good, and should not be used. The use of oversized shanks before they are needed will take years out of the life of a saw. Even
with proper tooth maintenance, the cutting edges of the teeth may not cut
properly unless they are aligned properly.
Many of the blades that come into my shop have teeth and shanks
that are well maintained. But
the blade will not work well, even after it has been hammered.
I have rescued blades from the sign painter by fixing the teeth and
shoulder alignment. How
to Check
The first thing to check is that the teeth are aligned with the shanks.
This is easily seen by closely looking at the teeth.
Most filers do this as they install teeth in the blade.
Where the problem comes is when the shoulders are not straight.
Even with the teeth lined up with the shanks, if the shoulders are
not straight, the teeth are not lined up properly with the blade.
The best way to check the shoulders is to make or get yourself a gauge.
Holding the gauge against each shoulder (after the gauge has been
set to account for any wear on the shoulder), you can quickly see where
the problems are. (This same gauge, with a different adjustment, can be
used to check the alignment of the teeth with the saw.)
You can also use a good straight edge held along the shoulder.
Make sure there is no gum on the blade where you are working.
When using the straight edge, make sure you compensate for the wear
of the shoulder. Use the edge
on both sides of the blade to get an eye for the amount of wear.
After years of use, the shoulders begin to wear.
As they become thinned, they loose the strength to stand up against
dodging hard spots. Older
saws with thin or weakened shoulders will often stray in the cut.
These worn shoulders will need to be looked at and aligned more
often. What
to Do
When you are sure a shoulder is bent, you can straighten it using a hammer
and a bucking bar. Place the bar just above the guide line (be
careful not to go in the guide line) on the side the shoulder is bent away
from. Hit the shoulder with the hammer near the outside edge of the
blade. It may take a few tries. After each time you have
tried, check the tooth's alignment with the shank and correct that before
checking the shoulder alignment.
Another way to bend the shoulders back to proper alignment is to use a
wrench. A good sized
adjustable wrench or what was called a carriage wrench will work fine, but
be careful it does not slip on you. As
above, it may take a few tries to get the shoulders back to plumb, and
after each try, align the teeth and shoulders before checking.
One important thing to remember. Never
try to bend a shoulder that has been welded unless you heat the shoulder
to 500 degrees Fahrenheit. 6.
FEED
Different
saws running at different speeds on different mills have different feed
rates. But every saw on any
mill running at any speed has the same rate of feed per tooth.
Most operations I've been to tend to feed too slow.
This is inefficient and can cause saw problems.
So can feeding too fast. You
will need to figure what rate to feed your blade for your mill to get the
best production and life out of your saw. How
to Check
What you want to find out is how far the log is traveling past the blade
in the cut for each revolution of the blade.
Take a look at a number of average sized boards you have cut.
Even with the best tooth maintenance, there is probably a tooth or
two that is cutting heavier than the others.
Each time that tooth cuts the log, it will leave a mark.
Measure the distance between the marks in the middle part of the
board. Unless you are feeding
at the maximum rate the carriage will feed, measure a few boards to get an
idea of your average feed. What
to Do
The
manufacture's recommended feed rate per tooth is 1/10" for hard or
frozen wood and 1/8" for softer wood.
The feed for your saw per revolution would be the per tooth rate
times the number of teeth. A 52 tooth saw cutting oak should have a feed
rate of nearly 5 1/4" (52 X .10" = 5.2") for instance.
If you cannot feed at the proper rate, you will need to change some things
on the mill. A blade with
less teeth would feed at a slower rate.
Slowing down the revolutions per minute of the blade will give you
more power to the blade. More
power from your motor or engine also could allow the proper feed.
If you are feeding too fast, you should slow down the feed. Too much feed can pack the gullets, causing a build up of heat. And if you pack the gullets full, the blade will quickly stop in the cut causing all sorts of problems. If you have the power to consistently feed too heavy, you might think about getting a saw with more teeth.
The teeth of
the saw are on the rim of a relatively thin disk of metal.
The main support for the blade is the collar, which is some
distance away from the teeth. The
guides help to keep the teeth straight in the cut.
The guide is used only to steady the saw.
Never use the guide to lead the saw. How
to Check
The guide should be set as high as possible to just clear the head blocks.
The pins should clear the bottom of the shanks by 1/4" or so. When the saw is turning, the guide should not touch the blade, but should be away from it just a little bit. You should just be able to see a hint of light between the guide and the blade.
The guide
itself should be tight and securely mounted.
And the pins should not be too large. What
to Do Move the guide to the proper position on the mill to be as high as possible and to 1/4" of the shanks. Set the clearance of the pins to the blade when the saw is running. 8.
PLUMB OF THE SAW,
LEVEL OF THE CARRIAGE The blade must be plumb and the head blocks level to make good lumber. How to Check
A blade that is not plumb with a carriage that is level will leave a dog
board (the last board) that is wedge shaped from top to bottom or edge to
edge. If the top of the blade
leans toward the carriage, there is a tendency for the saw to lead into
the log. And when the blade
leans toward the husk, the saw will tend to lead out of the log.
To check the plumb of the blade, use a good plumb bob and line.
Hook the line on a shoulder at the top of the blade, dropping down
so as not to hit the collar. The
line should not touch the collar or a tooth or shank.
A good spirit level is used to check the level of the head blocks and the
carriage track. Move the carriage along the track to check the level along
the entire length of the track. If possible, a heavy log on the carriage
for this check will show up any weak or soft spots in the track. A line
stretched along the guide rail and slightly above it can be used to check
for any bumps or dips in the track. To plumb the saw, you can wedge the bearing blocks of the mandrel as needed, or you can level the husk itself. The leveling of the carriage or the tracks depends on your mill and its set up. 9.
SAW HEATING
A blade that is running properly will be only 5 degrees warmer than the
air temperature. That slight
heating should only be in the rim from the friction of the teeth cutting
the log. If you have a blade
that is heating more than 5 degrees, it will not saw properly. How
to Check
After you
have sawed for a while and suspect that the blade is heating up, stop the
mill and feel the blade. Take
note if the blade is warm in the eye or the body or the rim.
Is it heating all around the blade or is it just in one section?
Where the blade is heating can tell you a lot about what is causing
the problem. What
to Do
If the saw is running hot at the eye or at the rim, go to that section of
this guide to help you find the solution. If it is heating only in a
section, it may have a fold or lump in it that might need to be hammered
out. Some thing to remember is that any heating of the blade can affect its performance. If the sun beats down on the saw, it can heat it enough to make trouble. If a slab gets wedged against the blade, friction will heat the blade in a hurry. So look around for anything that will cause heat. It only takes 5 degrees to make a problem. 10.
BENT ARBOR It isn't very often that this is a problem with a mill, but it can happen. It would be something to think about if you have hung the blade up in the cut, or pushed a log over onto the blade. How to Check
The most accurate method would be to use a dial indicator.
After you have secured the indicator, take a reading on the arbor
at the place on the arbor past the fast collar where the blade would be.
Turn the arbor. If the total indicator run out is more than .004",
your mandrel is bent beyond tolerance. Another check that will isolate the problem, but is a bit less accurate, would be to set the guide pins so they are the same distance from the saw blade. Turn the blade until it hits a guide. Take off the outside collar and pins and turn the saw 180 degrees without turning the arbor. Replace the collar and tighten it up as you would normally. Again, do not turn the arbor. Look at the guide. If the saw is touching the same side of the guide as before, the arbor might be sprung. If the saw is touching the other guide pin, the saw may be sprung (or "twisted" or "bent.) What
to Do
If your arbor is bent, it will have to be straightened or replaced. 11. SAW DISHED
A saw can be dished when the shanks are worn. As the shank wears, it loses its strength. This allows the rim to shrink or contract causing excess tension in the body of the blade. Replacing the shanks can sometimes take the dish out as the new, stronger shanks will stretch the rim, relieving the excess tension. If the collars are good and the shanks are not worn too much, but you still have a dish, it is time to get the blade hammered. 12.
SAW TENSION
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