HOMEMADE THICKNESS SANDER
by Nicolas Hambas
You can’t beat a thickness sander for saving hours of elbow grease and frustration when trying to bring a piece of wood to its final sanding stage. A commercial thickness sander is a wonderful machine but it will set you back the price of a used Honda. Besides, my production output can’t justify the purchase of such an expensive tool. What else to do but make my own thickness sander?
Here are some photos of the finished sander, each worth a thousand words, but here are some more words, anyway.
I started out by sketching out a rectangular base and establishing some dimensions. I decided on a 36-inch height that would allow me to work standing up without bending at the waist.
Then I settled on a 15” drum with a 12” useful width. To that I added the dimensions of the pillow blocks and the thickness of the lumber which added up to a 19” wide frame. I arbitrarily set the length of the frame to 36". I thought that would be an adequate length for the pieces I work with. The sanding platen is about six inches narrower than the drum to allow for the sandpaper clamps. For my use, a 12-inch sanding surface is wide enough. The widest piece I ever expect to put through is one half of a guitar soundboard. If I later decide I need a longer drum, I can replace the four crosspieces, the bottom shelf and the drum shaft, and make a new drum.
The platen is hinged on one end and free on the other. If you can picture the drum rotating clockwise, the hinged end is at three o’clock. The work is fed downhill from the high end toward the hinged end -- and against the rotation of the drum.
POSITIONING THE DRUM
I positioned the drum closer to the feed end by about 20 percent. I allowed two inches maximum clearance between the bottom of the drum and the top of the platen. If I ever need more than that, I can increase the height of the wooden blocks on which the bearings -- called pillow blocks -- are attached.
I used a 22” piece of a ½” steel rod as the shaft. The rod is a standard hardware item.
I purchased two ½” bore pillow blocks from a surplus outlet on the Internet. I didn’t really worry about the blocks’ exact outside dimensions, as I would adapt my sander to them. The bearings are equipped with an eccentric ring, used to fix the shaft onto the bearing.
I used a 3-3/4” heavy cardboard shipping tube for the body of the drum. You may use PVC pipe, or cardboard tubes sold as concrete forms instead. Everything else being equal, a larger diameter drum will take more sandpaper, and will have a higher sanding speed. This may burn the work and, if you loose control, it will catapult it with great force against whatever stands in its way – possibly your stomach.
I turned on my midi lathe two disks from ¾” thick pine. The outside diameter of the disks was equal to the inside diameter of the tube. I carefully drilled a ½” hole in the center of each. I epoxied one disk at each end of the drum and fed the shaft through before the epoxy hardened, to make sure that the holes would end up in alignment.
When the epoxy had hardened, I slid the drum to its final position on the shaft. That was not a very critical step, as the shaft was several inches longer than necessary. To secure the drum onto the shaft, I drilled two ¼” holes, each passing through the side of each disk, making sure that the drill passed through the center of the hole, through the shaft and out the other end. I counterbored both ends of the hole and secured each disk with a ¼” carriage bolt.
ATTACHING PULLEY AND MOTOR
I fixed a common, 1725 RPM motor equipped with a 2” pulley on a rectangular wooden base. If your motor is not reversible, figure out on which side of the drum you should locate the pulleys so that the drum spins in the right direction. The drum should spin against the direction of the feed. You could use a motor from an old sump pump if you can devise a safe method of fastening it to the base.
One side of the base is attached to the bottom shelf through a hinge. This leaves the other end free to rise off the shelf. The belt is shorter than the distance between the two pulleys. That raises the motor slightly, so that its weight keeps the belt taught. If your belt is too long, you may increase the distance between the two pulleys by moving the motor sideways away from the shaft pulley. Obviously, the two pulleys must be on the same vertical plane so that the belt runs flat.
The platen consists of two rectangular pieces of ¾” plywood screwed together for added stiffness. The surface of the platen should be flat and smooth, preferably covered in formica. It just so happened that I already had a couple of finished pieces of oak veneer plywood, so I skipped the formica part. The size of my platen is 12-1/2” by 32”. The platen is hinged unto the horizontal crosspiece of the base with two 2” common hinges. Because common hinges are rather loose, I intentionally misaligned them slightly along the base to keep them tight around their pins. A piano hinge would be preferable. If the top of the platen doesn’t make contact along the entire bottom of the drum, you may raise the hinge on the low side by loosening the screws, and adding a piece of veneer underneath.
PLATEN ADJUSTING MECHANISM
To control the distance between platen and drum, I used an 8-inch length of ½” threaded rod. On the top crossbar of the feed side, directly under the platen, I installed a 2-inch thick block of wood on which I had drilled an enlarged ½” hole for the rod to loosely fit through. I counterbored both sides of the hole to allow the installation of two ½” nuts. I fed the rod through both top and bottom nuts to align the threads and epoxied the nuts into the block. I fashioned a crank on the bottom end of the rod which I secured with two ½” nuts. At the point where the rod meets the platen, I attached a piece of metal so that the top of the rod wouldn’t eat through the wood. I also rounded the top of the rod on the grinder.
FINISHING THE DRUM
Now came the fun part. After I installed the pulley and motor, I slathered a ¼” thick layer of automobile body filler all over the drum. When that hardened, I placed a piece of straight lumber across the two horizontal pieces facing the cylinder, which I used as a tool rest for “turning” the drum. I switched the motor on and began to shape the drum with a rasp, one end resting on that piece of lumber. I continued refining the surface of the drum using a sharp chisel as my turning tool. So far, the job was mostly depended on eyeballing. When I had removed most of the high spots, I mixed a little more body filler and filled some obvious depressions.
There is no point in trying to make the drum as smooth as glass, because when it's wrapped in sandpaper any small depressions will be covered over. High spots, on the other hand, are totally unacceptable.
When the spotting filler hardened, I turned the drum again, using a sandpaper block. Finally, it was time to stop eyeballing and make sure that the job was true. I accomplished that by first attaching a piece of sandpaper onto the platen. Then I switched the motor on and slowly raised the platen. After stopping several times to move the sandpaper around, the surface of the drum looked nice and smooth, and the circumference of the drum became true to the platen.
The dust hood is the most important part of your machine because its main job is to keep your lungs and your shop free of dust. The hood also acts as a safety device in case the sanding tape breaks and starts flapping about.
Make a rectangular box that fits over the drum and rests on the blocks that support the pillow blocks. The box should be wide enough to allow room for the clamp screws to rotate freely. Add a square piece of ¾” plywood at the center of the top of the box, and drill a hole of a diameter equal to the OD of your favorite shop vacuum hose end. I used spare electrical parts from connection boxes to fashion clamps with which the box is attached to the base. You may use magnets, screws, clamps, eyehooks, weights; anything you can devise to hold the hood on top of the drum with the shop vacuum hose attached.
WRAPPING SANDPAPER ON THE DRUM
This machine uses aluminum oxide coated fabric tape sold in rolls at woodworking stores. In a pinch, you can use abrasive tape in rolls found in plumbers supply stores. It’s the same product, except it comes only in medium grit and narrow width.
To secure the tape onto the drum, you need two hose clamps of the right diameter. Insert both clamps and let them hang loosely onto the ends of the drum. Fasten the end of the abrasive tape underneath one clamp, at an angle to the drum. Turn the drum by hand and wrap the tape evenly around the drum. Make sure the edges of the tape don’t overlap. Cut the end of the tape from the roll. Keeping the tape taught, tighten the clamp to secure the tape.
That’s not an easy job to do, especially if you were born with only two hands, like most of us. A rubber band or a piece of masking tape may make the job of holding the end of the sanding tape easier. The direction of the wrap doesn’t make any difference.
When tightening the clamps, make sure that their fastening screws are placed at 180 degrees from each other to balance the weight of the spinning drum. Trim the protruding edges of the tape flush with the drum.
SURFACE SANDING ATTACHMENT
This attachment is a great timesaver. The pictures explain it best. I provided this attachment with baffles that stiffen the top and direct the airflow around the drum. The same mechanism that raises and lowers the platen is used to adjust the surface-sanding table. In using it, set the drum imperceptibly higher than the surface of the table. Do not lean on the work too hard. The rest is getting the knack of it.
You will notice in the pictures a bungee cord wrapped around the leg of the table and the height adjusting screw. This keeps the height adjusting screw from turning by itself while the sander is running. I’m sure there are more sophisticated contraptions for this purpose but the bungee cord works fine for me.
The machine is fairly light and attaching casters would make it unstable. Instead of casters, I fixed some nylon gliders on the feet of the sander. If your shop floor is uneven, you may have to reinforce the base so it doesn’t warp out of alignment as you move it around.
Work from the side of the sander. Start by pushing the work under the drum with one hand. Grab the piece as it exits from the other end with the other hand, and then finish the job by pulling the work through with both hands. By working from the side, if you lose control, the work will fly by, hopefully missing vital parts of your body.
Don’t try to remove too much material on one pass. Light sanding allows the machine to run easier and avoids burning the work.