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By: Eugene L. Larson
Copyright (c), 1981
Reproduced here in its original form and content.
INTRODUCTION
For many years I wondered how to produce wood
material comparable to the type and quality offered commercially by hobby
shops and mail order suppliers. Although the quality of commercial woods is
generally good, the variety is usually limited to walnut, cherry, bass, or
mahogany. This has posed a problem since I have wanted to experiment with
other types such as apple, pear, holly, poplar, box, ebony, dog, lime and
sycamore. Naturally, the solution is to prepare my own wood stock, but
sawing these woods on a standard table saw, a bandsaw,
or even a small 4 inch model saw left a rough and uneven finish which,
when sanded by hand, did not result in an accurate plank. A second problem
has been that from time to time I have encountered a thickness variation in
the hobby shop woods where a .031 inch (1/32 inch) board is actually .040 of an inch
thick. This variation is usually not critical except, for example, when
producing gratings using a .032 inch blade to cut the slots and finding that my 11.03111 inch commercial board was too thick to fit in the slots.
The solutions are either a wider saw blade (usually difficult to find odd
sizes) or a lot of careful hand sanding. We are all learning new and better
techniques every day as we build models. Some techniques are indeed new,
original, and significant breakthroughs whereas others are quite old but
had not crossed our paths before. Although the Thickness Sander falls into
the latter category, it is a significant advancement in my shop tools that
permits me to experiment. For example, a friend gave me a three-year old
black walnut log from his firewood pile, which I cut on my bandsaw and then finished into beautiful planks of
exact thickness in a matter of a few minutes. Using a bandsaw
to cut the wood close to the finished size and the Thickness Sander, it is
possible to maximize the utilization of wood and to minimize sawdust and
waste while producing accurate sizes.
BACKGROUND
I first learned of the practicality of
the Thickness Sander concept from Kent Wade of the Hampton Roads Ship Model
Society. He provided a demonstration of his unit during the annual, two-day
workshop in 1981 when the Tri-Societies (Washington, Richmond and Hampton Roads) met at Windmill Point, Virginia to "let the wood chips fly". Two of us
in the Washington Ship Model Society were so impressed with the sander's
simplicity and performance that we built our own. I constructed mine as an
attachment to my Shopsmith multi-purpose tool,
utilizing the lathe feature to turn the sanding drum, whereas Ken Dorr
constructed his as a stand-alone unit. The performance of both sanders was
outstanding, but the inconvenience of set-up and tear-down on the Shopsmith drove me to build the self-contained unit
described in this paper. I used my memory, the photos of Kent Wade's sander at the workshop, reference to the Ship
Modeler's Shop Notes of the Nautical Research Guild, and ideas from the
sander Ken Dorr built to construct this Thickness Sander.
BASIC CONSTRUCTION
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References:
A. Base Housing
B. Drive Motor
C. Drive Belt
D. Sanding Table
E. 3/4" Angle Iron
F. Piano Hinge
G. Sanding Drum
H. Pillow Block
I. Height Adjuster
J. "L" Bracket
K. 1/4" x 20 Nut
L. 1/4" x4" x 20 Bolt
M. Wing Nut
N. Cap Nut
O. Washer
P. Springs
Q. Dust Cover
R. Vacuum Attachment
S. Plastic Front & Back
T. Plastic Ends U. Friction Blocks
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References:
A. Base Housing
B. Drive Motor
C. Drive Belt
D. Sanding Table
E. 3/4" Angle Iron
F. Piano Hinge
G. Sanding Drum
H. Pillow Block
I. Height Adjuster
J. "L" Bracket
K. 1/4" x 20 Nut
L. 1/4" x4" x 20 Bolt
M. Wing Nut
N. Cap Nut
O. Washer
P. Springs
Q. Dust Cover
R. Vacuum Attachment
S. Plastic Front & Back
T. Plastic Ends U. Friction Blocks
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The Thickness Sander is built around a 1/6 horsepower
motor from a junked small bandsaw, which turns
at 1100 rpm. Any motor of adequate horsepower should be suitable. You
usually can find 1/4 horsepower motors at yard sales. Some motors, such
as the one I used, are end mounted. The mounting bolts were not long
enough to reach through the 3/4-inch side of the base. I purchased an
adapter for under $5.00, which provides a base mount for the motor (E.L. Walstedt Co., 11801 92nd
Avenue N., Osseo, MN
55369). I have the drum
turning at 1600 rpm, which is the speed I like to do the sanding. The
speed for any motor/drum assembly can be varied by the choice of
diameters of the pulleys. The smaller pulley goes on the sanding drum to
speed up its rotation. Use the equation:
Diameter of Motor Pulley =
Diameter of Sanding Drum Pulley x 1600 / Motor rpm
The construction begins with a
basic housing or box support structure (A) which has sufficient space to
accommodate the drive motor (B) and which will allow the drive shaft of
the motor to be far enough from the drum shaft so a standard drive belt
(C) can be used. The dimensions provided in the drawing are typical and
should be adjusted to your needs and hardware. The sanding table (D),
about I I inches by 15 inches, is a section of
3/4-inch shelving made from pre-glued pieces of clear pine purchased from
the local lumber company. A 3/4-inch angle iron strip (E) is placed
around the entire perimeter of the table to prevent warpage.
The sanding table is attached to the base housing at the front by a piano
hinge (F).
The sides of the base housing
are raised to provide the proper height for the sanding drum (G). This
height is determined by the drum diameter, bearing dimensions, and
maximum sanding thickness (I used about I inch). Pillow block bearings
(H) are laced on these raised sections. The type I used are ball bearing and cost approximately 910.00 each.
Cheaper sleeve bearings can be used, but I like these since they provide
good self-adjusting alignment and shaft securing features. I used
seven-ply 3/4-inch plywood for the base housing, and, therefore, used
dowels for plugs to accept the bearing screws to avoid weakening the
plywood. I did not want the screws coming loose during operation.
SANDING DRUM
The sanding drum (G) is
approximately 3 inches
in diameter and 10 inches
long and will just accommodate a standard sheet of abrasive paper such as
garnet or aluminum oxide. It has a 1/2-inch cold rolled steel shaft
inserted in the wood stock prior to turning to a cylinder. With this
method it is not necessary to drill the shaft hole on a finished drum,
which usually results in a centerline error. A 3 1/2 inch or 4 inch square stock should
provide sufficient wood during the turning of the drum to remove any
errors, which occur in drilling the shaft hole in the pre-turned wood. I
used an 18-inch x 1/2-inch drill and it came out 1/4 inch off center on
the square stock. If a long drill is not available, the drum could be cut
into sections.
Prior to turning the drum on
the lathe, holes were drilled in the wood along the shaft centerline and
through the shaft. The holes were just large enough to accommodate nails
with the heads cut off. The nails were placed in the holes, driven into
the wood on the other side of the shaft (using a second nail to reach
into the hole), and epoxied in place. This
keeps the drum from turning on the shaft. Be sure the nails are well
within the diameter of the final drum.
Next the drum is turned with
the steel shaft installed. The drive end of my Shopsmith
has a drill chuck attachment, so that was easy. For the other end of the
shaft, I drilled a 1/2-inch diameter hole I inch deep in a block of wood
1 1/2-inches square on the sides and 2-inches long (put the hole in the 1
1/2-inch square face). This piece of wood was placed on the shaft and
centered on the lathe tail-stock. The drum was turned to as close a
dimension as possible, but I wasn't worried about inaccuracies since they
would be taken out later. The abrasive paper must be installed later.
FINAL ASSEMBLY
The base housing, as shown in
the drawings, turns out to be a completely closed box with four sides, a bottom
with the motor mounted on it, and a "table" top. The base
housing should provide for the proper ventilation of the motor. There
are, of course, many variations on the size and shape of the housing
depending on personal requirements and preferences.
After the base (A) is
constructed, the sequence of assembly starts with the installation of the
motor (B) in a manner which allows movement up and down to loosen or
tighten the drive belt (C). Once the separation of shafts is determined,
a permanent spacer can be installed between the motor and the base to
make a rigid assembly. Next install the pillow block bearings (H),
sanding drum (G), and drive belt (C). Be sure the drum rotation is such
that the bottom of the drum comes toward the work you are sanding,
otherwise the wood will fly out the other side. The table (D) is last
since it is easier to do the prior assembly with it removed. Attach the
table to the base with a piano hinge (F) at the front. You could choose
to place the hinge at the rear which results in sanding down the incline.
This is more awkward for me, but does place the height adjuster at the
front. Ken Dorr's approach was to make the rear about I inch higher than
the front and he placed the height adjuster at the front. Therefore,
there is a built in upward slope to the table which reduces to nearly
level as the table is raised for thinner cuts.
HEIGHT ADJUSTER
The height adjuster (1) is
installed on the end of the table opposite the hinge. I used a simple
mechanism consisting of a cut off "L" bracket (corner brace)
(J) purchased at a hardware store, and a 1/4-inch, 20 threads per inch
nut (K) silver soldered to it at the inner screw hole of one leg. A
1/4-inch by 4-inches long, 20 threads per inch bolt (L) with a wing nut
(M) soldered at the head is then threaded into the nut, and a cap nut (N)
is placed on the top. The cap nut rides in the hole of a washer (0)
secured to the bottom of the table. (You might have to drill out a little
wood in the table above the hole in the washer so the cap nut seats
properly.) Finally, two light duty springs (P) are installed between the
bottom of the table and the base providing tension to prevent the table
from bouncing.
TURNING THE DRUM
Now comes the "moment of
truth" when you find out how nearly round and straight you turned
the drum. If the drum is not round you will have an undesirable but
"pretty" ripple effect on your finished wood. If the drum is
not turned straight one side of the wood being sized will be thicker than
the other. These inaccuracies are easily taken out of the drum by: (1)
laying a piece of abrasive paper on the table, sanding side up, (2)
starting the motor, and (3) slowly raising the table. As the table with
the abrasive paper laying on it reaches the drum you will hear a "thump-thump-thump"
as the high points are sanded off. Continue
raising the table until a perfect match is obtained between the drum and
the table. Be sure to move the abrasive paper around on the table as the
sanding action progresses. As a last step, put pencil marks on the drum
and when they are removed evenly the drum is finished. Apply a light coat
of sanding sealer on the drum. When dry, sand lightly and apply contact
cement to the drum and to the abrasive paper you will use on the drum. (I
used a number 100 grit, but you could put a
coarse grit on half the drum and a fire grit on the other half.) Attach
the abrasive paper to the drum and trim the excess length with a straight
edge and razor.
CALIBRATION
In calibrating the
approximate planing ability of the sander, the
following method is used. If the drum is located close to half way
between the hinge point and the height adjuster, as in this design, then
for every inch the height adjuster is raised, the sander will remove 1/2
inch. (However, do not try that much at one time!) Therefore, one turn of
the bolt is 1/20 inch or .050
inch, which will remove .025 of an inch of wood.
It follows that 1/4 turn of the bolt will remove .006 of an inch. If you
reference a clock, 5 minutes of turn (1/12 turn) will remove
approximately .002 of an inch of wood, which is pretty good control. This
can be summarized in a table:
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Fraction of
Turn
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Clock
Reference
(minutes)
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Removes
(inch)
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1/12
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5
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.002
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1/6
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10
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.004
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1/4
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15
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.006
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1/2
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30
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.125
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1
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60
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.025
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You could calibrate the
height adjuster for the actual thickness, but the accuracy will vary as
the abrasive paper wears. It is easier to use a micrometer to obtain
the desired thickness.
USE
The Thickness Sander is now
finished. The only thing to remember is to always feed the wood against
the rotation of the drum to prevent it from becoming a missile. To
avoid damaging the table when sanding a very thin piece of wood, place
the wood to be sized on another, thicker piece which has already been
run through the Thickness Sander which insures it has a constant
thickness. You can sand down to .005 of an inch or so, if the wood will
hold together. Do not expect to take off 1/8 inch on each pass, instead each pass through the sander should
remove a small amount of wood. Your original rough cut wood should be
quite close to the final dimension to save wood and to prolong the life
of the abrasive paper. Woodworking suppliers sell an excellent
rubber-like bar, which keeps the abrasive paper clear of clogs and
extends its life so that frequent replacement is not necessary.
There are many potential
uses of the sander in addition to planing
wood sheets to the proper thickness. One is to sand the edges of planks
such as 1/16 inch by 1/4 inch. This can be done by gluing a fence on a
separate board, lining up the planks to be sanded against the fence,
and pushing the entire assembly through the sander. Gratings can be
made perfectly flat after assembly by passing them through the Thickness
Sander several times, removing a little wood at a time to avoid tearing
them up.
DUSTCATCHER OPTION
As a
added feature to keep you shop cleaner and to avoid fine dust
everywhere, a cover (Q) can be made to f it over the top of the drum.
As can be seen in the drawing, the combination wood and plastic cover
is made to fit snugly on the base. I like the plastic because I can see
and control the actions better. On top of the cover is an adapter (R)
to fit a shop vacuum. If the plastic pieces surrounding the drum are
given a clearance of about 1/4 of an inch, very little dust escapes.
The sides and top of the catcher are wood. The front and back (S) are
1/8 inch plastic screwed to the wood, and come to within 1/4 inch of
the table in the fully raised position. End pieces of plastic (T), with
close cutouts for the shaft, are cemented between the front and back
plastic very close to the drum. The dust cover is held on the base by
friction (snug fit) utilizing pieces of wood (U) attached to the ends,
thereby allowing easy removal.
VARIATIONS
The Thickness Sander
principle can be adapted to various tools for motive power. As
mentioned at the beginning of this paper, I used a Shopsmith
to turn the drum of approximately the same size. This was highly
successful except for the inconvenience I noted. The Ship Modeler's
Shop Notes of the Nautical Research Guild describes mounting the table
on a metal lathe. A Unimat lathe would be a
good source for power and would provide a bed for the table; however,
the drum would have to be smaller. With some ingenuity a Dremel tool could be adapted to do the job, as one
of our club members has done.
Have fun working with new woods!
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For
some updates and some revisions to consider see Art
Herrick's notes on the Seaways FAQ.
There is also a shop note on a thickness sander
using a drill press in The Nautical Research Journal Volume 43,
Issue Number 1, March 1998, page 62.
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