Home-made Thickness Sander
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- The concept of the thickness sander or abrasive planer has been around for several hundred years in one form or another according to R. E. Brune in an early Guild of American Lutherie publication. The following general directions for creating one were written because so many visitors to the shop expressed interest in the one I made about 10 years ago. It was loosely patterned after several designs from the early Data Sheets from the Guild of American Luthiers, now recompiled and improved in their first book publication, "Lutherie Tools". I do not in any way claim that the one shown on this webpage is the best, etc. but it has worked well for me and if one is patient in using it, results can be accurate to within .002-.003" or better.
- Before going much further, it is important to note that what results here is a real power tool, driven by a 1/3-1 HP motor that is capable of producing a variety of injuries very quickly if safe work habits are not observed. Since most folks tend to feed wood toward the drum which is rotating toward the user, a slip of the hands can result in the wood being ejected toward the user at injurious speeds! Don't use this when tired, under medication which causes drowsiness, etc. The author writes this article as a community service, but assumes no legal responsibility for the final functionality of this machine.
- The photo shows the object under discussion. No beauty prizes for this one, but it works. The construction is simple and robust. The framework is made up of half-lapped 2x4's glued and bolted together with 1/4" nuts and bolts. The framework is about 3' long, 3' high and 16" wide. The width of course is decided by what size instruments one is going to build. Since I was only making smaller instruments ten year ago, I made it this size. For guitars, it should probably be at least 24-30" across.
There are 2x4 cross-members top and bottom at each end and both sides, and a plywood sheet connects all four of the lower cross-members for stiffness. Note that there are two shelf brackets at the base of two of the legs to keep the sander from wandering. The upper cross-members at each end serve two purposes: on the end away from the operator, the cross-member supports a piano hinge which in turn connects to the planer table; On the operator end, the cross-member contains imbedded 5/8" nuts top and bottom through which a long 5/8" bolt with handle at the base goes in order to adjust the table height. The upper cross-members on each side support the pillow-block bearings for the rotating cylinder.
The hinged table is a pair of 3/4" thick, solid-core mahogany sheets measuring 1'x3', but remember this width is for smaller instruments. Consider the width of the instruments you plan to make and then add at least 3-4" to make the final table width. The upper surface is covered with Formica for its entire length in order to make pushing the wood against the rotating cylinder a more low friction process. On the operator end there is a piece of aluminum or iron angle bar that the end of the 5/8" bolt rests against. If the table were longer this
wouldn't be necessary, but some sort of small metal plate would be in order to reduce wear on the underside of the table surface. The longer the bolt the better since the length of the bolt and the placement of the cross-member at that end determines how thick a piece of wood can be sanded. I used the longest carriage bolt I could find for this one, but it's not really long enough for greater than 1" material. Threaded rod would produce a more flexible set of options and can be bought in lengths as long as 3' from most hardware stores. I suggest a useful rod length might be 15-18".
- Let's now go on to the drum and bearing mechanism. The bearings on either side which support the shaft are called "pillow blocks" for reasons which escape me. In any case they can be purchased from Maguire Bearing, MSC, Enco or any number of places dealing with machine tools and/or bearings. Installation instructions should come with the bearings, but it's fairly straightforward by inspection. Machine shops and/or retail ironworks dealers will sell smooth shaft material by the foot. Take the pillow block with you to be sure you get the right stuff. The shaft is usually permanently fixed to the pillow block with a pair of set screws which come with the block; exercise caution when making a temporary fit that you don't score the shaft. If the clearances are small, you may have difficulty removing the pillow block from the shaft because the deformed surface won't readily slide by some part of the bearing surface. My small sander has a 5/8" diameter shaft but a larger (wider) one may well need 3/4". I've never had problems with wobble or whatever, but it's probably better to be a little conservative here.
I actually counter-sunk and through-bolted a pair of 2x4's to the shaft, with each 2x4 having a snug-fit dado groove in it slightly shallower than 1/2 the diameter of the shaft. I used 4 pairs of 1/4" bolts to hold things on and ten years later no problems.
To round the pair of 2x4's to a cylinder, I treated the spinning shaft as though it were a lathe piece. IF YOU DO IT THIS WAY USE EXTREME CAUTION!!! With another 2x4 C-clamped across the frame as close as possible to the spinning piece, I slowly removed material with a sharp roughing lathe chisel, checking often for the nearness of the bolts to the surface. When I got as close as I was comfortable with, I removed the cross piece and placed a 1' wide piece of 80 grit sandpaper on the sanding table and holding firmly to the paper, slowly raised the table to contact the spinning cylinder using the 5/8" bolt adjuster. Considering various alternatives, this approach is a fairly safe way to make the cylinder surface parallel to the table face. If you try to hold the table by hand, the cylinder will have flat spots and rattle noisily at every speed.
Much dust is raised in this operation, and this is probably a good time to put the dust collector in place. You must use a dust collector of some sort because the amount of dust generated by this machine is incredible. Very thin-walled PVC pipe such as that used in gutter downspouts works well and can be cut with a fine-toothed blade on the bandsaw or with a
saber saw. I used a Shop Vac for a vacuum source for 6-7 years and hated it because it was soooooo noisy. I now have one of those high volume low pressure vacuum systems which would be fine for low noise levels if the bearings weren't wearing out on the cheap imported motor.
Attaching the sandpaper to the cylinder is an irksome problem. For this sander, I chiseled a groove 1/4" deep and 3/8" wide to fit a piece of aluminum strip that I had. The strip has 6 evenly spaced holes in it and holds sandpaper in place by friction. Wood screws work OK as do deck screws. When the holes become too large, I just put a few drops of superglue and several toothpicks to fill them up again. This is a very forgiving machine. Other folks use 2-3" wide cloth-backed sanding tape and affix it with screw tabs or contact cement. Another area for creativity here...
I now use a 1 HP motor left over from an imported belt sander whose bearings cratered after a year or so. Earlier I used a 1/3 HP motor for many years, but it did bog down pretty regularly. The pulley at the shaft is about twice the diameter of that at the motor, but I recommend that you buy the pulley with the three different diameters so that you can see for yourself what speed works best for you. The new motor on this sander is placed to the side of the framework rather than underneath on the plywood sheet either because the motor would only run in one direction (of course the wrong one) or because I was too dull-witted to figure out how to reverse it the day I installed it. The motor should be fixed to a sheet of 1/2-3/4" plywood and the plywood in turn connected to the framework base by a pair of hinges. An adjustment screw through the plywood board and framework base allow loosening or tightening of the tension on the V-belt connecting the motor and the sanding drum.
I've tried many kinds of sandpaper but for general roughing I've settled on 3M Resinite Floor Surfacing Paper, Type E 100 grit-2/0 roughness. 80 grit gouges horribly and 150 seems to wear out within a few minutes (although I'm probably asking too much from it at the time). It should be remembered that it's worth it to make the few final passes with a higher grit paper to avoid dealing with larger scratches later on.
The above does not pretend to be an exhaustive account of making and using the abrasive planer, yet sufficient details are present to make a pretty good stab at putting one in place in one's shop. I will be more than willing to do my poor best at answering questions by e-mail to anyone who attempts to build such a device for their
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