Build a surface sander that's every bit as smooth on your budget as it is on a board.
Chances are, if you're only an occasional woodworker, you'll never really need a surface sander. But if you do a fair amount of woodcrafting, this 12 inch homebuilt surface sander tool will make a nice addition to your shop.
The framework is made of 16-gauge (about .070 inch), 1 inch-square tubular steel stock . . . which can be replaced with a heavier-walled material if necessary. The table is a 3 foot-long section of 3/4 inch plywood cut from a cabinet door; that 7-ply birch panel was an excellent choice because it's resistant to warp and has an extremely smooth finish. The sanding drum and feed rollers were fabricated from hardwood disks and dowels, respectively. The drum is spiral-wrapped with 1 inch aluminum oxide machinist's cloth held with adhesive, and the rollers are covered with 1-1/2 inch reinforced rubber hose sections.
To keep the surface sander design uncomplicated, the drum is powered, but the feed rollers operate manually with a hand crank. The infeed and outfeed rollers turn in unison, since they're connected with a V-belt. As you might imagine, drum sanding requires appreciable horsepower, even for a benchtop unit like this. Our sander performed satisfactorily coupled to a 1-HP, 1,750-RPM capacitor-start motor, though a split-phase type would work just as well because starting torque requirements aren't that critical. By using a 5 inch drive pulley, we were able to achieve about 3,000 RPM at the sanding drum . . . the equivalent of 3,450 surface feet of sanding per minute.
The sander's depth of cut is adjusted by raising or lowering the table, which is mounted on a bed hinged to the base to form a parallelogram. A length of threaded rod fastened between two clevis shafts on the base and table bed sets the table height. Any irregularities in the surface of the workpiece are taken up by spring-loaded pinion guides, which allow the rollers' axle shafts to rise up slightly under pressure from below.
We've provided both an exploded illustration identifying the machine's parts and dimensioned plan views to aid you in putting together your own sander. Furthermore, we've gleaned a few tips from our research shop that should help you make the transition from paper to project as pleasant as possible.
Probably the most intimidating component is the drum, which must be assembled carefully, since it'll be exposed to a good deal of stress when the tool's in operation. The 12 inch long wooden cylinder is composed of a dozen 1 inch by 4-3/8 inch disks glued together and pinned to a 1/2 inch steel axle. Though the pieces-or the whole drum — could be turned on a lathe, we used a 4-1/2 inch fly cutter bit in a drill press to cut the hardwood circles. (A band saw, scroll saw, or carefully wielded coping saw could be used as well.)
With the disks cut and 1/2 inch holes drilled in their centers, an aliphatic carpenter's glue or a plastic resin can be applied to cement the pieces together on the shaft. For extra insurance, you should pin the last disk (opposite the pulley) through the axle . . . which will then serve as a locator for positioning the entire drum. To be certain, trial-fit the axle and mark the hole before actually gluing the disks in place. Once the drum's fully cured, true it on a lathe or mount it in the pillow blocks and drive it with the pulley so you'll be able to cut it to a true 4-3/8 inch diameter with a chisel and temporary tool rest.
The feed rollers also require some attention, though their precision isn't as critical because they don't turn at high speed. Each is made from an 11-7/8 inch section of 1-1/2 inch banister dowel (or hardwood turned to that dimension), but instead of having straight-through axles, they use pinion shafts made from 1/2 inch lag screws. It's important that these pinions be centered in the rollers, so mark your starter holes very carefully before drilling the 11/32 inch pilot holes, especially when setting up the longer 6 inch lag bores at the pulley ends.
Once the pinions are secured, you can cut off the heads and true the rollers as you did the drum. Don't remove too much stock, though, because the rubber hose sleeves must fit snugly over the rollers, even though each gets pinned at the pulley end.
When setting up the table frame, remember that it must remain level as it's raised and lowered. The best way to guarantee this is to be sure the holes in the hinge posts are exactly the same distance apart in each piece, and that the hinge pins in the bed and base are spaced equidistant as well.
The control mechanism simply uses the threads on the rod to hold the table at the desired height. The shorter, base-mounted clevis shaft is cross-bored and tapped for 5/16-18 thread, while the bed-mounted piece gets a full 5/16 inch hole to allow the rod to rotate freely (it's captured with locking nuts on both sides of the shaft). Both clevis shafts are end-drilled and tapped to accept the 1/4-20 machine bolts that serve as mounting pivots.
In preparation for using the sander, it's important that you set it up correctly. The roller frame must first be leveled by adjusting the nuts on the four 1/2 inch stanchions, and the tension on the pinion guides set so the rollers distribute equal (but not too much) pressure on the work. When wrapping the sanding belt around the drum, do it in a spiral, or "barber pole," pattern, and use a contact adhesive so you'll be able to change the belt easily. Since the drum must rotate toward the workpiece as it's being fed, wrap the belt in that direction, so it'll tend to tighten rather than loosen as it spins. (If necessary, secure the ends of the belt with staples sunk near the drum's edges.)
And, for safety's sake, never operate the sander without its drum and belt guard attached, and don't stand directly in front of the work as you crank it in, since it could kick back on you. Also, make a habit of using closed coat sanding belts, which are made to handle high drum speeds.
Even an occasionally used project is worth building right; take the time to make this one worthwhile, and its performance will reflect your extra effort.
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