Before reading this paper, I might suggest you look at Eugene Larson's 1981 paper entitled, CONSTRUCTING AND OPERATING A THICKNESS SANDER FOR SHIP MODEL BUILDERS, which will give you some background and reference, especially noting the two drawings of Eugene's machine.
At the 1982 Nautical Research Guild's fall gathering at Philadelphia, during Sunday morning's Round Table Discussions, I had the opportunity to see Eugene Larson's Thickness Sander, and the following year built my own machine.
This project may seem like an intimidating one for those of you with nothing but ship model making hand and small model maker's machine tools; but with some contracted assistance [as I used] from your local cabinet maker's shop and a machine shop, it can be readily accomplished with a reasonable investment, considering the most useful machine that you will end up with.
You should also compare the price of building your own machine to buying a commercially built ready-to-run Ship Model Maker's Thickness Sander; but it will not have a 3 inch thickness capacity under the sanding drum, the 10 inch sanding drum width, or in one case the drive motor horse power of the machine pictured and described in this paper. See the machine manufactured by Preac Tool Co., Inc.. Also Byrnes Model Machines Thickness Sander.
For the use of a Thickness Sander in ship model construction see Eugene Larson's 1987 paper, YOUR OWN LUMBER MILL FOR SHIP MODEL BUILDERS.
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| The author shown with the sander. |
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There are three machines that ideally should be used in some of the operations described below. They are a drill press, a router, and either a hand held power saber saw, a powered jig saw or a band saw. If you do not own these machines, I am sure most model shipwrights have a friend who does, or have some of the construction operations done by your local cabinet shop.
The machine was designed with a maximum 3" gap between the sanding table and the sanding drum. This allows me more than enough capacity to attach stock, with two faced tape or other means, to a 3/4" Birch faced plywood auxiliary table and pass it through the machine, e.g. sizing short pieces of thick or thin stock, sanding assembled hatch gratings or other assemblies to final thickness. You can also vertically clamp short thin pieces of stock, by installing a carpenter's miniature Bench Top Wedge Clamp on an auxiliary table, so you can square up their edge, reduce their width or taper them. For details of what I refer to as a Bench Top Wedge Clamp, see John Kopf's Timber Taper Tool.
The above are just some examples of how useful this machine can be, beside just for sizing long pieces of wood strip stock. Just let your imagination go to work for you !!!
For the above plywood parts, I went to my local cabinet maker's shop, who with precision and my parts sketches, supplied the plywood from his scrap pile, and cut all the parts to their envelope shape, and then dry assembled them with #0 wood biscuits. All done in 1982 for $32, which is say about $56 in today's dollars.
A wood biscuit joint between two pieces of plywood is made by a machine that cuts one or more matched circular bottomed slots in each piece. This allows you to insert in the slots, a special football shaped piece of compressed hardwood called a biscuit. The biscuit serving as a spline between the two pieces. These #0 wood biscuits are 1 3/8" long by 5/8" wide.
To me, having the machine's housing sides and it's base, the dust collector housing, and the pillow block mounting blocks dry assembled with wood biscuits - IS THE SECRET !! - of building this machine, because of the ease of pre-aligned assembly, and the strength of the final glued and wood screwed assemblies. When glued the biscuits swell, making a very strong and tight glue joint between two pieces of edge to face, wood screw assembled, plywood parts.
As to the machines adjustable sanding table … the Birch faced 5-ply type of plywood used, with a polyurethane finish on both sides, assures that it stays flat, and it's top work surface will not ware excessively fast. If, or when it ever starts to show ware, just lightly sand and re-finish it, before allowing it get down to bare wood.
An alternate sanding table work surface, is to face the plywood with a Formica type laminate material. Being sure to cover both the top and bottom of the table, so with humidity change and the difference in expansion of the table's materials, the laminate top and bottom will neutralize any warping or bowing of the table.
I added two pieces of 12" long 1" x 1" x 1/8" angle iron, fore and aft, on the bottom of the 11 1/8" wide x 16" long sanding table, not to keep the table flat, but to add 1.6 pounds of weight to keep it seated down in it's adjusted position, and to assure the machine's table has "no bounce" to it when the machine is in operation. Note: Angle iron is sometimes not really flat, so only snugly secure it to the table bottom with a wood screw at each end, using an oversize screw clearance holes in the angle, to avoid warping the tables' surface and provide for expansion differences. Note: Oil the table's piano hinge, so the table can move as freely as possible.
Round topped access ports were cut in the two housing sides, and a round cornered access port in the front, for access to the motor for drive belt tension adjustment, and to allow circulating air for the motor. The housing was then glued and screwed together, and to its base with #8 x 1 3/4" Flat Head wood screws, and finished with polyurethane. The housing is 13 1/4" wide x 14 1/4" deep x 11 3/8" tall, with the front and back faces set back 1/8" from the ends of the sides. The housing base is 15 1/4" wide x 16 1/4" deep; which is larger than the housing. The machine is bolted to a base cabinet, which in my case was a short depth [14"] two draw filing cabinet, purchased from a second hand office equipment dealer.
The motor is mounted on it's own plywood base, and to the machine's base with a piano hinge, so that there is a tension adjustment for the drive belt. When adjusted for the correct belt tension, the motor base was locked down, by putting a fitted wood shim under the motor base and locking it down with two wood screws. By fixing the motor in place, there is no excessive downward force exerted on the sanding drum shaft by the weight of the drive motor hanging from it, and as a result the machine probably runs smoother.
I had given to me, a pair of FAFNIR, PB 1/2" - 11-V, pillow block bearings, which are a tight slide fit on the drill rod drum shaft, are self-aligning, have sealed pre-lubricated bearings, with a shaft lock and a heavy stamped steel mounting frame. I would suggest shopping around at industrial suppliers, to see what is now available.
One source of pillow block bearings is Small Parts Inc., Miami Lakes FL., with a choice of bearings listed in their Catalog. Their product line, in general, is a great hard-to-find odds-and-ends source for model makers.
My preference for mounting the pillow blocks was mechanical fastenings for an installation like this. I used two pieces of the 3/4" Birch faced plywood 6 1/4" long by 1 1/8" wide, which were located on the top of the housing sides with a wood biscuit, and Epoxy glued and screwed in place. These mounting blocks were pre-drilled for 1/4-20 Hex Head bolts for mounting the pillow block bearings, and had 1/4-20 "T' Nuts countersunk into their bottom surface. "T" Nuts are readily available at your local hardware store, and are a machine-threaded insert with a round mounting flange, for use in wood where you wish to use a machine bolt fastener.
For the sanding drum wood stock, my local cabinet shop supplied me with two 1 5/8" x 3 1/4" x 10" pieces of maple. With a 1/2" dia. Core Box Pattern Bit [half round] in my router, I cut a half-round groove down the centerline of each piece and clamped them together, around the drum's steel shaft. Using a drill press, a countersunk [1/4" dia.] 3/32" hole was drilled through the longitudinal center of one of the half's and through the shaft into the other half, and a 1 1/2" long x 3/32" dia. hardened steel dowel pin was installed to insure that the maple drum would never spin free of the steel shaft. A hardened steel dowel pin should be available from your local machine shop.
To hold the two drum half's together, they were pre-drilled for countersunk [3/8" dia.] installation of six, 1 3/4', # 10 Flat Head wood screws, three screws on either side of the shaft, from opposite sides of the half's. Be sure to center the screws in the block for drum balance. Before un-clamping, pre-install the six screws, lubricated with soap or wax, which will speed up the final assembly when you glue the two drum half's together around the steel shaft.
The drum half's and shaft were then Epoxy glued, screwed and clamped together. The six countersunk wood screw holes and the countersunk shaft dowel pin hole were filled with glued in, face grained, maple plugs, supplied by my local cabinet shop. Six 3/8"dia. plugs for the screws, and 1/4" dia. for the dowel pin.
The drum/shaft assembly was then taken to my local cabinet shop, where they planed off the corners of the drum blank till it was 3 1/4" hex shaped, and then set it up on a wood lathe, using the pre-machined turning centers in the shaft. Fortunately their industrial duplicator wood lathe had a traveling tool carriage which assured the drum had the same diameter throughout its length, and they turned the drum down to a 3" diameter. They used a dead center in the head stock spindle, a live center in the tail stock, and using a faceplate they dogged the drum shaft to the faceplate. At the very most, less than one hour of chargeable shop time.
If I built another machine, I think I would extend the run-out portion of the table, say another 3 or 4 inches, for better support of long stock exiting the machine. This would require a small bevel on the top of the back housing piece, when the table is in the maximum up position.
When assembling the sanding table's .040 x 1 1/4"(open dimension) steel piano hinge to the back inside face of the housing, I first temporarily removed the two angle iron weights from the bottom of the table. Then the piano hinge was first secured even with the bottom back edge of the sanding table, and then loosely secured with it's bottom even with the top of the inside edge of the back face of the housing, with only one screw in the center of the piano hinge, allowing the table to pivot on the screw.
The table was then held up against the sanding drum and fixed in place, using two 1 1/2" square x 12" long blocks of wood, which were held up against the bottom outside edges of the table and up against the inside of the housing sides, and clamped in place to the housing sides. Then the rest of the screws were installed in the piano hinge, and the clamping blocks removed. This set up a very close parallel alignment between the sanding drum face and the table top, which only required some fine tuning as described next. On my machine the initial misalignment was only about plus or minus 1/64".
To assist in running the abrasive faced plywood back and fourth under the drum, I glued wooden handles to the top face of both ends. I should note that I had my local cabinet shop run the 11" x 18 " piece of plywood through their thickness sander to assure it's two faces were parallel.
Both ends of the 10 degree angled abrasive tape are trimmed parallel with the ends of the drum, making the ends of the tape taper to about 3/4" wide. I have a permanent metal template for marking the end taper of the tape for trimming.
We all know what extreme humidity can do to sandpaper in the summer, but with this method if the abrasive strip expands, you simply loosen one end and snug up the spiraled abrasive strip and refasten it with a new piece of two faced tape. Note: There is a smooth polyurethane finish on the drum, so two faced tape will readily adhere to it.
For "two-faced tape", a roll of 3M Co., Scotch Brand #467 is used. This tape is about .0035 or so thick, of solid sheet adhesive [no core], 1/2" wide, on a waxed paper carrier tape. This strip of adhesive is impervious to normally incurred heat and cold, will not creep, has a seemingly endless applied life, and the adhesive is extremely aggressive. It is a commercial product that can be found at Industrial Suppliers who carry 3M Co. products, and I find many uses for it in my shop. #467 tape was originally developed for use in paper making plants, for connecting rolls of paper as they were processed through the manufacturing machinery.
For me, the 120 grit abrasive tape gives a suitably smooth sanded surface and the abrasive surface does not seem to load up excessively fast, and can be readily cleaned with a gum rubber cleaning bar. Check with a Woodworking Machine supplier for the availability of rolls of abrasive cloth backed tape in other grits and widths. As an option, you can always mount two different grits of tape on the drum at the same time, which opens up the possibility of designing the machine with a slightly longer sanding drum.
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| Details of the adjusting mechanism. |
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Two brass 3/8-16 hex nuts were used to guide the threaded rod as it is run up and down, and are mounted to two pieces of 1 1/4" x 5/8" x 1/8" aluminum angle which are bolted to the housing's 8 1/8" high front face. The nuts were riveted to the angles using three #18 gauge brass escutcheon pins, trimmed to an appropriate length for riveting. So the threaded rod would turn easily and smoothly in this assembly, it was run in with some valve-grinding compound. With the threaded rod lightly oiled, the resulting sanding table height adjustment mechanism has a smooth running and very solid feel to it.
To act as a thrust bearing for the table's height adjusting screw, a 3/8"-16 Cap Nut is installed on the top end of the threaded shaft, with it's rounded cap running in the center hole of a flat steel washer on the bottom of the sanding table. This 7/16" inside diameter washer is fastened to the table with three #18 x 3/8" brass escutcheon pins [nails].
Note in the pictures of my machine there is a vertical calibrated scale that shows me the rough distance between the sanding drum and the table. For the table's fine height adjustment, I know that turning the hand wheel so many degrees, raises or lowers the table a certain distance. Note the degree markings on what I call the hand wheel, which came out of my odds and ends box. One source of these Engraved Drum Dials is ALLIED DEVICES, Baldwin NY.
A simple 3" diameter hardwood disk, say 1/2" thick, sandwiched between two washers and jam nuts on the lower end of the threaded rod, could serve as a hand wheel. With radial marks on its top outside edge, at say every five degrees; would give you a reasonable adjustment reference. I still continually measure the stock thickness with a micrometer dial caliper during a stock sizing operation, so I know exactly what the machine is doing.
The clear face parts of my dust collector housing were made from Lexan, so if ever the cloth abrasive strip gets loose from the sanding drum, or a small piece of hardwood stock gets loose from an auxiliary table, they will not shatter the 1/8" thick Lexan, as say acrylic plastic might shatter. The bottom of the front and back Lexon faces of the dust collector align within 1/8" of the bottom surface of the sanding drum and the table, with the table in it's maximum up position. This keeps your fingers and knuckles away from the sanding drum - a most important safety factor ! Remember this is a powerful machine, and as such demands the usual respect.
For the four Lexan parts, find a plastic fabricator or window glass shop, and have them supply the material and cut the parts for you, to their envelope shape. After trimming the front and back pieces, permanently screw them to the dust collector housing. Have the two Lexan end pieces initially cut slightly wider so they can be trimmed to fit snugly between the between the two Lexan faces after they are screwed to the housing. Then scrape the end surfaces smooth and bond the four joints to the face pieces using a thin cyanoacrylate glue [Instant Glue].
I felt I wanted to mechanically fasten the dust collector housing to the machine's sides, since the housing is also serving as a very important Safety Guard, can be bumped easily and dislodged while operating the machine, and that the shop vacuum hose is already exerting a backwards force on the housing. I was also aware that I would continually be removing the housing to clean the sanding surface of the drum, so I should be able to do this with a minimum of effort.
To accomplish this, I drilled clearance holes for two 1/4-20 Thumb Screws, down through two diagonally opposite ears of the dust collector housing's plywood ends. I had already pre-drilled two matching holes in the pillow block bearing mounting blocks, and installed 1/4-20 "T" Nuts, countersunk into the bottom of the blocks. A 1/4" inside diameter steel washer is used under the head of the thumbscrews, so they do not chew up the plywood.
When I started the machine back up, I neglected to also turn the shop vacuum back on, and was unaware of this due to the sound of the machine's drive motor. With the first piece of polar half way through the machine, "I glanced up", and there was a large cloud of very fine poplar sanding dust starting to form in my shop.
Right then and there, I took the time to install an electrical outlet box on the side of the machine for the shop vacuum's power source, with the box wired in between the machine's on/off switch and the drive motor. Since then, when the machine is turned on, the shop vacuum is also turned on - No more unexpected sanding dust clouds !!
I hope my thoughts about the design and building of this machine, will prompt the reader to build his own Thickness Sander. As a model shipwright, you will wonder how you ever got along without one ... and as I have previously said, it will not cost you an arm and leg. There is also nothing like the personal satisfaction of building, and then operating a most useful machine !
Surely I was not the first, or was I the last one, to build a Model Shipwright's Thickness Sander, so I can not help but think of the late John Shed of Model Shipways Co.; who use to remind us - that there is always another and possibly better way to build a mouse trap.
Sometimes in John Shed's old ship model kit catalogs he use to insert a cartoon character of a mouse standing on his hind legs dressed in an ancient seaman's clothes and a brimmed hat, with a "buckled leather pant's belt" draped over his fore leg. The cartoon's caption read:
Text and photographs:
Copyright © Arthur R. Herrick, Jr. – Westmoreland NH - October 2002
{Art Herrick}
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