Jointers are simple machines with few moving parts, but the two beds,
the fence and the cutterhead all have to be in alignment for a jointer
to function properly. Few things are more frustrating or more common
than problems with jointers. This is especially true when you're trying
to get straight, square edges on your boards. I've come up with a
six-step tune-up that should set your jointer straight. It's easy to do
and will only take an hour or two, depending on how many problems you
unearth.
Jointers are supposed to cut straight, square edges, but all too often, they leave a sniped or a bowed edge (see
"Common Problems").
Snipe results whenever the top of the outfeed table dips below the
knife's top cutting arc. A bow cut results whenever the outfeed table
rises above the cutting arc. A cutterhead that's not parallel to the
outfeed table, or tables that are not parallel to each other, will make
it impossible to get the table height set just right for all fence
settings.
Common jointer problems result in a sniped or bowed edge. Adjusting the
outfeed table height usually cures the problem. However, if both tables
and the cutterhead are not in perfect alignment, the problem will
return when you move the fence. This tune-up procedure takes care of
all the possible misalignments that can cause jointer problems.
The Right Stuff
You will need a
few tools to perform this tune-up: A good straightedge, a set of feeler
gauges and machinist's metal shims are must-haves for this job. For
some steps, a dial indicator is easier to use than a straightedge.
The straightedge, shims and feeler gauge run about $80 total. The
optional dial indicator with a magnetic base and extension arms adds
another $33 and is well worth the cost. All these tools can also be
used to set and tune-up other shop equipment and to check your own work
for flatness (
see Sources, page 6).
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A precision straightedge is
essential. You can perform all the tune-up steps using this 50-in.
precision straightedge that costs $58. Unlike inexpensive
straightedges, this one has a precision-ground edge with a tolerance of
.003 in. along its entire length. Such a good straightedge is not
cheap, but it's a good investment for your shop. |
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A feeler gauge set is
used in tandem with a straightedge to measure very small gaps. If the
straightedge reveals a gap, you can measure that gap by finding the
feeler gauge that fits under the straightedge. |
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A dial indicator with
magnetic base and arm can't be beat for tool setups. A number of these
six tune-up procedures are best done using a dial indicator. Like the
straightedge, this tool is also useful for other machine setups. |
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Metal shims align jointer
parts. Variety packs are convenient and easy to use. A strip of
aluminum cut from a soda can is a quick substitute for a .005-in. shim.
That coupled with some .001-in. shim stock should cover all your
tune-up needs. Shims can be stacked to create any desired thickness. |
Fine-Tuning Your Jointer
Step 1: Check For Flat Tables and Fence
Check each table and the fence for flatness (
Photo 1).
The accuracy of later measurements depends on flat tables. Measure for
dips or a droop using the straightedge held parallel to the table bed.
Then, hold the straightedge diagonally across the table to check for
twist. The good news is that finding twist or dips in the table is
highly unlikely. The bad news is that if you do find things out of
whack, you can't do much about it. In extreme cases, a messed-up fence
or table may be reground at a machine shop. You'll have to weigh the
cost in time and money against simply buying a new jointer. If your
jointer is under warranty, talk to the manufacturer.
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PHOTO 1:
To start your tune-up,
check each table for flatness. Lay the straightedge on a table and use
the feeler gauge to check for gaps. A gap of .003 in. or less is
acceptable. 2Infeed and outfeed tables that are not in the same plane
across their widths need to be made coplanar. (With any luck, your
tables aren't this bad.) |
Step 2: Align Tables
It's not unusual for the two tables to be out of parallel across their widths (
Photo 2). It's easiest to check the tables for parallelism with a dial indicator (
Photo 3).
You can also do the check with a straightedge. Hold the straightedge
down on the middle of the infeed table so it extends over the outfeed
table. Set the infeed table to the exact same height as the outfeed
table. Slide the straightedge over to the fence side of the table and
use feeler gauges to check for gaps. Repeat with the straightedge on
the user side of the table.
Align your tables by shimming the outfeed table. Loosen the outfeed
table's gib nuts and lift the table so you can insert metal shims on
the side of the table that's low (
Photo 4). Shim the outfeed table only because it is moved very little and the shims are less likely to shift during table adjustments.
Recheck the tables and make any necessary shim adjustments until the tables measure in exact alignment.
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PHOTO 2:
Infeed and outfeed tables
that are not in the same plane across their widths need to be made
coplanar. (With any luck, your tables aren't this bad.) |
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PHOTO 3:
Check the tables for
parallelism across their widths. Bridge the dial indicator from the
center of the infeed table to the center of the outfeed table and zero
it. Slide the indicator across the width of the table to measure any
difference in height. |
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PHOTO 4:
Bring the tables into
alignment by inserting metal shims on the low side of the outfeed
table. Choose a shim thickness equal to the amount your table was off.
Loosen the gib nuts and lift the table while you insert the shim or
shims. Then retighten the gib nuts. |
Step 3: Fix Sagging Tables
Tables can also be out of alignment along their lengths (
Photo 5). Use the straightedge to see whether the table end dips below the infeed table (
Photo 6). Correct a dip by adding shims to the top or bottom of both gib ways on the outfeed table (
Photo 7).
Retighten the gib nuts and check the tables again. Make any necessary
adjustments until the tables lie in the exact same plane.
An hour
of your time
yields
a lifetime of
perfect
accuracy
from your
jointer.
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PHOTO 5:
Tables can be out of
parallel along their lengths. Typically, the tables sag on the ends.
This is especially true on older jointers that have worn gib ways. |
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PHOTO 6:
Check for table sag by
holding a straightedge tight against the infeed table. Set the infeed
table height so the straightedge just contacts the outfeed table. Then
use a feeler gauge to determine the amount of dip or rise in your
outfeed table. |
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PHOTO 7:
Correct a sagging table
by shimming the bottom end of the two dovetailed gib ways on the
outfeed table. A table that dips toward the cutterhead would be shimmed
at the top end of the gib ways. |
Step 4: Level The Cutterhead
With The Tables
Now that the tables are parallel to each other along their lengths and
widths, it's time to make sure the cutterhead is parallel to the
tables. If the cutterhead is not level with the tables, your cut will
be heavier on one side of the table than on the other. Jackscrew
cutterheads allow you to set the knives to compensate for this;
spring-loaded knives or a segmented carbide insert cutterhead do not.
The fix for this problem is so simple that I recommend leveling your
cutterhead no matter what type of knife holder you have.
Use a dial indicator or straightedge to check cutterhead alignment (
Photo 8).
If the cutterhead is off, measure the exact amount on the low side.
This equals the size of shim you'll need to raise the cutterhead (
Photos 9 and 10).
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PHOTO 8:
Check that the cutterhead
is parallel with the tables. Rotate the cutterhead so the knives are
below the table. Clamp a guide board parallel to the cutterhead. Set
the dial indicator against the guide board so the plunger contacts the
cutterhead. Zero your dial indicator; then slide it back and forth. |
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PHOTO 9:
I removed the cutterhead
here to illustrate how it is mounted. Two threaded rods attached to
pillow blocks run through holes in the base and are held in place by a
nut and a washer. Place shims between the pillow block and the jointer
bed casting. |
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PHOTO 10:
The cutterhead is easy
to shim. Remove the drive belt and loosen the bolts that hold the
cutterhead in place. Lift the low end of the cutterhead and insert
shims under the pillow block. Then retighten the bolts. |
Step 5: Set Proper Knife Height
To minimize kickback hazards, jointer knives should not project more
than .020 in. from the cutterhead. (Owners of spring-loaded cutterheads
have a knife-setting gauge that automatically sets the proper knife
projection.) A potential hazard exists with knives set parallel to the
outfeed table: It's easy to unintentionally set the knives so they
project too far.
A dial indicator is the best instrument for checking knife projection (
Photo 11), but you can make do with a straightedge and feeler gauge.
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PHOTO 11:
Proper knife projection
increases jointer safety by limiting the cut's aggressiveness. Use a
dial indicator set to zero on the cutterhead. With your hand on the
pulley, rotate the cutterhead backward. As the knife rides under the
dial indicator, it should read no more than .020 in. |
Step 6: Set Proper
Outfeed Table Height
Your knives should be set so that the very top of the cutting arc, also
referred to as top dead center, is the same height as your outfeed
table. We used the straightedge to accomplish this task (
Photo 12),
but a dial indicator is another option. To do this, set the dial
indicator on the outfeed table and zero it. Then set the plunger over
the cutterhead with the body of the indicator on the outfeed table.
Rock the cutterhead back and forth; the indicator should hit zero as
its highest mark. Check this at several points along the width of the
table. Repeat for all three sets of knives.
Edge-joint a couple of boards to test your jointer (
Photos 13 and 14).
In practice, it often takes a little tweaking of the outfeed table
height to get it just right. Often the table ends up set .001 or .002
in. below the cutterhead. Now your jointer is ready to go and should
create perfect edge joints every time.
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PHOTO 12:
To set the outfeed table
height, place a straightedge on the outfeed table so it projects over
the cutterhead. Rotate the cutterhead backward and raise or lower the
table until the knife barely kisses the straightedge when it's at top
dead center. |
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PHOTO 13:
Fine-tune the outfeed
table height by edge-jointing a couple of boards that are narrower than
the fence height and no longer than the infeed table. |
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PHOTO 14:
Put the newly jointed
edges together and hold the joint up to a light source. No light leaks
indicate a jointer that's perfectly tuned. If you are getting a snipe
at the end of your cut, raise the outfeed table a bit. If the jointer
puts a concave edge on your board, lower the table. Repeat the process
with the fence set at the far edges of the table. The results should be
the same, and that should put a smile on your face. |
Sources Lee Valley Tools, (800) 871-8158,
www.leevalley.com 50-in.
aluminum straightedge, #05N63.05, $58. Dial indicator and magnetic base
and arm, 88N31.20, $33. Feeler gauges, #86K99.01, $14. Brass sampler,
6-1/2 in. x 6 in., .001 to .010 thickness, #27K07.50, $7.