Tune Your Bandsaw

Tune Your Bandsaw_133_lead

Tune Your Bandsaw

6 adjustments
deliver professional
results.

By Mark Duginske

I love bandsaws, even though they have a reputation
as troublesome tools. I suppose that’s why
I like them, because I enjoy investigating woodworking
machinery. I’ve tinkered with dozens of
14″ bandsaws, trying to understand how they work
and how they should be set up. Here’s what I’ve
concluded: most bandsaws benefit from a tune-up.I’ll show you six procedures
to improve your saw’s performance. I’ll demonstrate
these steps on a standard cast-iron 14″ saw,
but they apply to just about any type of bandsaw.
Once you complete your inspection of your own
saw and correct any problems (or learn to live with
your saw’s limitations), I’ll show you how to adjust
it for a typical blade.

The alignment procedures we’ll perform are a
one-shot deal. You shouldn’t have to re-check your
saw again. The tensioning, tracking, and guideadjustment
procedures must be followed every
time you change blades, however.

Before we begin, let’s review the major parts of
the saw and what they do.

 

Align the wheels

If you look at the upper wheel on your 14″ bandsaw, you’ll
notice that it has a crown: the center is higher than the
edges. The crown exerts a pulling force, moving the blade
to the top of the wheel. In a well-tuned saw, both wheels and
their crowns are coplanar (in line with each other). This
allows the blade to run as straight as possible. If the wheels
aren’t in alignment, they compete with each other for control
of the blade. This isn’t a problem for narrow blades, but
aligned wheels improve the performance of wide blades,
such as those you’d use for resawing.

1) Unplug your saw. Remove the blade, then unbolt and
lift off the table (Photo 1).

2) Install a 1/2″ wide blade and tension it according to
the saw’s scale. Some authorities skip this step and align
the wheels without a blade. That isn’t correct, because the
saw has to be under tension when the wheels are aligned,
to simulate real running conditions. A wider blade requires
more tension than a narrow blade, and it’s best to align your
wheels under the most tension they’re likely to receive. On
most 14″ saws, the largest blade you’ll use is one that’s 1/2″
wide. Back off the upper and lower guides and thrust bearings
so they’re at least 1/8″ away from the blade.

3) Open both wheel covers and place a long straightedge
across the wheels (Photo 2). If the wheels aren’t parallel,
turn the tracking knob behind the saw to tilt the upper wheel
forward or backward. Once the wheels are parallel, you can
determine whether or not they’re coplanar (Figure 3).

4) If the wheels are not coplanar, determine how far one
wheel must be brought forward. Measure the gap between
the straightedge and the wheel. If the gap is less than 1/32″,
your wheels are sufficiently coplanar and you can skip
ahead to step 6. If the gap is greater than 1/32″, one wheel
should be adjusted.

5) To re-align a wheel, remove it from its axle and add
or subtract bushings (Photo 4). On most saws, you can
only remove one wheel, not both, without using specialized
tools. On Delta saws, the upper wheel comes off easily;
on most other brands, the
lower wheel comes off. The
bolt that secures the wheel
has a left-hand thread. Turn
it clockwise to loosen it. If
your wheel must be moved
in, and there are some bushings
behind it, simply remove one or two, corresponding to the gap you measured above.
Replace the wheel and you’re ready to move on. If your
wheel must be moved out, measure the axle’s diameter and
purchase a few machine bushings at the hardware store.
Standard washers work OK, but are about 1/16″ thick.
Machine bushings are thinner (about 1/32″ thick). Once
you’ve put the wheel back on, replace the saw’s table and
re-install the blade.

 

Track and tension

Before moving on to the next step, your blade must be
adjusted to run in the center of the wheels. This is called
tracking, and it’s a procedure you follow each time you
change blades. The correct method is to steadily increase
tension while you track your blade, so you’ll make both the
tracking and tensioning adjustments at the same time.

6) Unplug the saw. To begin, the blade should be under
very little or no tension. Rotate the upper wheel by hand
and slowly increase tension (Photo 5). After a few revolutions,
note where the blade sits on the upper wheel. Adjust
the tracking knob to move the blade in or out (Figure 6) as
you continue to rotate the wheel. Keep rotating the wheel
and adjusting the tracking knob until the blade is under full
tension and tracking in the middle of the wheel.

7) Check the blade’s tracking under power. Close the wheel
covers and plug in the saw. Turn the saw on for a second and
then turn it off again. Open the top door and see if the blade
still tracks in the wheel’s center. If it does not, make a minor
change in the tracking knob’s position, and check again.

 

The tension squabble

I wouldn’t be a bit surprised if you’re confused about blade
tension. A lot of misleading information has been published
about it, and I’d like to set the record straight.

Some folks claim that the tension gauge on your 14″ saw
is erroneous and that using its indicated settings doesn’t
deliver enough tension. They would have you replace an old
spring with a new one, replace a standard spring with a more
powerful one, or purchase an aftermarket tension gauge to
substitute for the one on the saw. None of this is necessary.

First, old springs don’t wear out, and don’t need to be
replaced. Second, most springs provide adequate tension.
The exception would be a spring that is fully compressed at
its highest tension setting. This spring should be replaced
with a more powerful one. Third, the scale on your saw
may not be perfect, but as a rough indicator, it’s adequate
for the purpose. According to my measurements using the
best aftermarket tension gauge available, these scales are
accurate enough.

For most work, you’ll get good results with the tension
gauge set at the mark corresponding to the blade’s thickness.
But if the blade isn’t sharp, or the workpiece is especially
thick, increase the tension one mark. In any case, no saw will
perform well unless it’s tuned up first.

 

Square the table

It’s easy to understand why your bandsaw table should be set
at 90° to the side of the blade, but did you ever check whether
it was also square to the back of the blade? This is important
for advanced joinery techniques such as cutting tenons or
dovetails. It will also help in the next alignment check, squaring
the guidepost.

8) Raise the guidepost as high as it will go. Remove the
throatplate if it sits proud of the table (it should be exactly even,
or, better yet, a little low in front and high in back). Loosen
the trunnion bolts and tilt the table side to side until it rests solidly
on its 90° stop (the stop is usually a bolt located under the
table’s left side). Tighten the trunnion bolts.

9) Place an accurate square alongside the blade. If the table
isn’t square, adjust the stop.

10) Place the square behind the blade (Photo 7). If the table
isn’t square in this axis, shim the front or back trunnion (Photo
8). You can use any hard material for shims, including a cut-up
soda can. This can be tedious, but it’s not difficult. The screws
that fasten the trunnion to the table may be hard to access. If
so, remove the table from the saw. You will lose the trunnion’s
position when you loosen all of its screws (it must align properly
with the lower trunnion), but the correct position isn’t hard to
regain. After inserting the shims, loosely tighten the screws and
return the table to the saw. Tighten the trunnion bolt, which
will pull the upper trunnion into position, then tighten the
trunnion screws.

 

Adjust the guide post

On a well-tuned saw, the guide post runs parallel to the blade.
When you raise or lower the guidepost to accommodate material
of different thickness, the blade guides and thrust bearing are
always in the correct position relative to the blade. If the guide
post doesn’t run parallel to the blade, you’ll have to readjust the
positions of the side guides and thrust bearing each time you
move the guidepost up or down to saw wood of different thickness.
That’s a situation you can live with, but you don’t have to.

11) To check your guide post, the blade must be tracked and
tensioned, and the table must be square to the blade. There are
two ways to proceed. The easiest method is to lower the guidepost
as far as it will go and plane a short stick, of minimum thickness,
to fit between the post and a 12″ square (Photo 9). Or you can
remove the lower guide assembly from the guide post and place
the square directly against the guidepost.

12) To re-align the guide post, you must tilt the entire upper
casting of the saw. First, remove the blade. Next, loosen the bolt
that connects the saw’s upper and lower sections. Place brass
shim material in the joint to tilt the guide post front-to-back
or side-to-side (Photo 10). It takes trial and error to find shims
of the correct thickness. Tighten the joint before checking the
guide post. Once the guide post is square, go back to the start
of the alignment checks (Step 1) and check that the wheels are
still sufficiently coplanar.

 

Round the blade

Rounding the blade
protects the thrust
bearings. This is an optional step, but it increases the life of your blade
and thrust bearings. The rounder the back, the less likely the
blade will crack. The stone also smoothes over the welded
portion of the blade, so it can’t scar the thrust bearings.

13) Turn on the bandsaw and round the back of the blade
with a stone (Photo 11 and Source, below). It will take about
five minutes. Begin with the corners, then round the rest of
the blade’s back.

 

Adjust the guides

Many of the procedures above are one-time only adjustments,
but every time you put a new blade in your saw you’ll have to
reset the guides and thrust bearings. Here’s how to do it right.

14) Back off the thrust bearings above and below the table.
Adjust the side guides, above and below the table, so they
don’t touch the blade. Track the blade in the center of the
upper wheel.

15) Position the guide assembly about 1/4″ above your
workpiece. Adjust both thrust bearings so they’re about
.015″ behind the blade (Photo 12). That’s equivalent to
four thicknesses of a dollar bill, or four pieces of standard
weight (20 lb.) printer paper. Whatever system of measurement
you use, it’s important that both bearings sit an equal
distance behind the blade.

16) Adjust the side guides forward or backward until
their leading edge is about .015″ behind the blade’s gullet
(Photo 13). Be sure to adjust the guides below the table,
too. When you cut, the blade will bend backwards and ride
against the thrust bearings, but the blade’s teeth shouldn’t
contact the side guides. The narrower the blade, the more
care you should invest in getting this setup just right.

17) Adjust each set of side guides close to the blade
(Photo 14). The gap should be very small, but not so close
that the blade contacts the guides when it’s not cutting
wood. If you have bearing guides, rather than blocks, make
sure that the guides are rotated in such a way that their
high points are directly opposite one another. The lower
guides on some saws are hard to access. You may find that
tilting the table makes them easier to get to through the
throatplate opening.

Source

(Note: Product availability and costs are subject to change since original publication date.)

Highland Woodworking, highlandwoodworking.com, 888-241-6748, Blade
Rounding Stone, 486031.

 

 

 

This story originally appeared in American Woodworker January 2008, issue #133.

Purchase this back issue.

Click any image to view a larger version.

A Visual Guide to Your Bandsaw

Tune Your Bandsaw_visual guide

Tune Your Bandsaw_1

1. Begin aligning
your saw
by removing the
table. It’s easy
to do. Take off
the blade, then
unscrew and
remove the knobs
under the trunnions.
The table
just lifts off.

Tune Your Bandsaw_2

2. The first alignment check is to see if the saw’s wheels are
coplanar (lying in the same plane). Tension the blade,
then place a long straightedge across both wheels. Tilt the
top wheel so that it’s parallel with the bottom wheel.

Tune Your Bandsaw_3

3. Here’s what you
may find
using
the straightedge test.
In A, the straightedge
touches at four
points. The wheels
are coplanar, and
you’re all set. In B,
the wheels are parallel,
but don’t lie
in the same plane.
Measure the gap
behind the straightedge.
In C, the top
wheel must be tilted
before you can determine
whether the
wheels are coplanar.

Tune Your Bandsaw_4

4. The fix for wheels
that are out of
alignment
isn’t hard.
You simply pull
off one wheel and
remove or install a
machine bushing or
washer to act as a
shim. Some wheels
can’t easily be
removed, however,
so you may have to
live with a misalignment
problem.

Tune Your Bandsaw_5

5. To prepare
for the next
step
you have
to re-install the
blade and track
it in the center of
the wheel. Slowly
bring the blade up
to tension as you
rotate the upper
wheel by hand.

Tune Your Bandsaw_6

6. Adjust the tracking knob to center the blade (A).
Turning the knob counterclockwise (B) tilts the upper
wheel and moves the blade forward. Turning the knob
clockwise (C) tilts the wheel in the opposite direction and
moves the blade backward.

Tune Your Bandsaw_7

7. After centering
the blade
on
the upper wheel,
place a 6″ square
behind the blade. If
there’s a gap at the
top or bottom, the
table isn’t square
to the blade.
Measure the gap
with shim stock.

Tune Your Bandsaw_8

8. Shim one of
the trunnions

to adjust the
table. Remove the
table to access
the trunnion’s
mounting screws.
To start, insert
shims that are the
same thickness
as the gap you
measured above,
in Photo 7.

Tune Your Bandsaw_9

9. The third alignment
check
is
to see if the guide
post is square to
the table, front-toback
and side-toside.
Place a wood
spacer between
your square and the
guidepost to get an
accurate reading.

Tune Your Bandsaw_10

10. Align your
guide post

by shimming the
saw’s column.
Loosen the bolt
between the saw’s
upper and lower
sections. Place
shims in the joint
to tilt the column
and guide post.

Tune Your Bandsaw_11

11. Now that
your saw
is aligned
, turn
your attention
to the blade. It’s
a good idea to
round the back of
a new blade with
a dry oilstone.
Removing the
back’s sharp
corners will
extend the
blade’s life.

Caution: This operation causes
sparks. Disconnect your dust collection
system from the bandsaw.

Tune Your Bandsaw_12

12. Adjust the
upper and
lower thrust bearings

about .015″
behind the blade.
That’s equivalent
to the thickness
of a dollar bill
folded twice,
making four layers.
Remove the
guard to make
this measurement
easier to see.

Tune Your Bandsaw_13

13. Adjust the
forward
position
of the
upper and lower
guides. The
front edge of the
guides should be
slightly behind
the bottom of the
blade’s gullet.

Tune Your Bandsaw_14

14. Adjust the
clearance

between each
guide and the
blade. The gap
should be about
.004″, which is
the same as the
thickness of a
dollar bill. You’re
all set to saw.