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While researching information on building ukuleles I came across a discussion on shop made drum sanders. I contacted one of the participants regarding the sander and a ukulele builder from Hawaii contacted me and offered to send me a copy of the plans. I am in the beginning stages of easing into ukulele building so I thought I would take a crack at constructing the unit. I have seen plans for larger drum sanders that seemed very complicated. This plan is really basic and didn't seem like it would be a huge undertaking. The following information recaps the construction process including some of the problems I encountered.
MATERIALS
I was concerned about investing a significant amount of money into something that may or may not perform up to my expectations. Therefore, I chose to use kiln dried 2X4s instead of the hard maple that was called out in the plans. As a result, some modifications were necessary as I went along and if I were to build another one I would do some things differently. I will point these areas out as I step through the project.
Most of the materials can be found at your local home center or hardware store including the steel rod for the drum shaft. The plan called for a ¾ HP motor but I opted for a new 1 HP motor I purchased from Harbor Freight. The pillow block bearings were purchased at my local bearing supply store and the power switch was purchased from Rockler. The only unusual supplies were the velcro matting and sandpaper that I purchased from Woodmaster Tools.
The following is a list of costs I incurred for constructing the sander.
1 HP Motor - $90.67
Pillow Block Bearings - $49.35
Lumber & Bolts for Base - $33.46
Hinges/Shaft/Fasteners - $38.85
Paint and Casters - $10.55
Power Switch - $19.35
Velcro Matt and Sand Paper - $52.75
BASE and DRUM CONSTRUCTION
I started by working on the base and the discs for the drum. The lap joints for the base were cut on the radial arm saw and the discs were cut on the bandsaw from 3/4" plywood.
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The plan called for pinning the lap joints with dowels. I decided to go with a combination of lag bolts and hex bolts and nuts because I was afraid that the dowels wouldn't hold up over time due to the vibration. This way I can just tighten the bolts every now and then keeping the base from racking. An 8 degree bevel is sanded on the back support rail to provide clearance for the feed table when it is in the uppermost position. The bevel was a pain to make uniform with a belt sander. The bevel is not along the entire length of the piece and I didn't investigate a better way of doing it prior to assembling the base. And depending on the hinge type used to attach the feed table I am not all that sure that the bevel would be necessary and I will touch on that a bit later as well. Lastly, I installed some 2" rigid casters on the rear base assemblies and put a couple of coats of paint on it. I installed an eye bolt on the front cross member to hook onto to when moving it around the shop.
There is one other thing I want to mention regarding the base assembly. Using soft wood for the part of the frame where the pillow blocks attach would not have been a wise move. One of my aunts friends was visiting from Ohio and we started this project together while they were here. He suggested that we add a piece of hardwood on the top braces. I don't think I would have thought of this so my thanks to Howard for pointing it out to me. I ripped a piece of 1 x 1 ½ quartersawn oak and joined them to the 2X4s with biscuits. If I did it again with 2X4 construction I would also use hardwood for the three of the other rails where the table, motor mount and elevation controls attach.
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FEED TABLE and ELEVATION CONTROL ASSEMBLY
The feed table is constructed of 2 pieces of ¾" ply laminated together. I called a local cabinet maker I found in the yellow pages and he was more than happy to sell me some of his scrap laminate for a dollar a sheet. This works great as long as you are not picky about the color. I ended up with a mustard yellow color that looks just fine next to the green base. I used oak for the trim pieces and cut a recess to allow the table to elevate high enough for the drum to be just shy of reaching the table top.
I asked the ukulele maker that sent me the plan if there was anything he would do different if he was to build another sander. He said that the threaded rod for the elevation control was eating into the bottom of his feed table and suggested putting a piece of metal on the bottom of the table. That is probably what I would have done but my visitor friend, Howard, had a buddy that he was in the military with that lived up the road a couple of hours away. Howard went to visit him and took the threaded rod with him. His friend is a machinist. He put it on the lathe and turned the end down to about ¼" or so and made a brass bushing for the shoulder of the threaded rod to ride on. It works great. There is enough clearance to effectively work throughout the entire travel from the lowest table height to the highest without binding. The large shop made wing nut on the end of the threaded rod was 8" long according to the plan. The motor I chose had an on/off switch on the front of it. When I mounted the motor the wing nut hit the motor when raising or lowering the table. So I made a 3 ¼" hand wheel that would clear the motor.
Initially, I attached the feed table to the base according to the plan using 4" T-Hinges. I attached them to the underside of the table first and then set the table in place and, from underneath, marked and drilled the mounting holes. If I remember correctly, I think the table was about 2/3 of the way up when I attached the hinges to the base. When I raised the table to within about ¼" from the top it started to bind really bad. I also noticed that the T-Hinges had quite a bit of play in them and the table rocked back and forth. Not good. So, after beginning to shape the drum, I decided to do what Howard had suggested before he left and that was to use the leftover piano hinge (used to attach the motor mount to the base) for attaching the table. This time I raised the table all the way to the top before attaching the other side of the piano hinge to the base. This worked out perfect. The table is now rock solid and will travel up and down without binding. So, depending on how wide the piano hinge is it may be possible to raise the table all the way up and attach it without having to cut the 8 degree bevel in the first place. I have not confirmed this but it is a possibility.
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In the photo above you can see the pieces of oak that were added to the top braces for mounting the pillow block bearings. If I would have mounted them to the soft wood they would have compressed the wood fibers, when tightening the bolts, and not been perpendicular to the shaft. This would have caused problems with the shaft binding even though the pillow block bearings are self-aligning.
My original intention was to get a receptacle and wire an extension cord to it for the power switch . I attended the Sacramento Woodworking Show a couple of weeks ago and the Rockler router table switch was on sale so I purchased it along with a link belt for the motor. One good thing about the link belt is that if you forget to put it on before assembling the drum in the pillow blocks (like I did) you don't have to take the assembly all apart to slip on the belt.
MOUNTING THE MOTOR
First, I propped the motor up on some wood blocks high enough for the piano hinge to rest against the rail that it attaches to. Using a straightedge I aligned the shaft pulley with the motor pulley and made a mark on the rail at the edge of the hinge. I found it much easier to lay the base on its side to install the motor mount hinge. I used a small quick clamp to clamp the feed table to the base to keep if from falling back. When it was on its side, again, I used wood to block it up so the mount and the hinge were at the same height. I aligned the hinge with my mark on the rail and installed the screws. For mounting the other side of the piano hinge to the motor mount I chose to use 10-24 machine screws with locking nuts due to the vibration factor. If I notice a problem over time with the screws in the rail I will just drill them out and use machine screws there as well.
SHAPING THE DRUM
It was during the shaping of the drum that the slop/play in the original T-Hinges became evident. As I pushed the feed board (covered in 60 Grit paper) under the drum it got very tight near the end as the table would flex up. I replaced the T-Hinges with the piano hinge and then completed the shaping of the drum with no presence of binding. The only other problem I noticed was that there were small ridges where the softwood ply met the hardwood ply. That is why I think MDF would have been a better choice for the drum discs. However, the ridges were not noticeable after the Velcro matting was applied.
MATTING AND SANDPAPER ANGLE
The folks at Woodmaster provided me the information for determining the proper angle needed on the ends of the matting and sandpaper. This process will ensure you get the proper angle for the specific size that your drum ends up being after final shaping. Simply take a piece of string and wrap it around the drum. Mark the string at precisely the location where they intersect. With the matting or paper laying on the bench, place the end of the string on a corner of the material and stretch the string out until the mark is at the opposite edge of the material and mark this point. That is the proper angle for your drum. Use a straightedge and utility knife and cut the angle. Then wrap the material around the drum (before taking off the backing in the case of the matting) and mark the other end where it meets the edge of the drum. Cut the same angle on that end and you are ready to install the material. Take your time with the matting because you can't have any bubbles and once it goes on it pretty much ruins it if you try to remove it.
FINE TUNING THE SANDER
To test the sander and fine tune it I ran a piece of scrap through the jointer and planer so it was nice and square and flat. I placed the board under the drum and raised the table until it barely touched the board. I slid it across the table checking the difference from the bottom of the drum to the top of the board. The left side was tighter and I had to lower the table to get the board all the way to the left end. So I decided to make some shims to place under the pillow blocks to raise that end of the drum. I had some sheet metal so I sandwiched it in-between two pieces of ply to keep it flat when drilling the holes for the pillow block bolts. I measured the distance between the bolt holes and marked this on the plywood. I used a couple of screws to sandwich and index the plywood together. I drilled the holes on the drill press and used the first shim as a template for the others. It took 3 shims to even out the two sides of the drum.
After running some pieces I am satisfied with the result. It is not going to provide the precision of a factor built machine with power feed capability. Results are largely based on the operator maintaining a consistent feedrate and it helps to turn the board end for end each time you run it through. This seems to even things out a bit. I don't know how much each rotation of the elevation control knob raises the table but a ¼ turn is about all that is needed between settings. Much more than that it will be too difficult to feed and may cause damage to the matting.
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GUARD AND DUST CHUTE
I completed the guard that will incorporates a dust port for hookup to my dust collector. I made the ends of the guard from some poplar that I had left over from a previous project. The plan called for a piece of stove pipe or 6" PVC to be cut in half and set into a radiused rabbit in the end pieces. Neither of these was readily available so I just made the end blocks square and used 3/8" plywood for the pieces that make up the guard. The hole for the dust collector was cut on the drill press with a fly cutter. The guard is attached via flathead machine bolts that screw into threaded inserts that I installed in the top of the base. Once I had the basic box constructed I attached it to the base and connected it to the dust collector to test it for effectiveness. The dust collection wasn't all that great because there was too much open space around the gaurd. I took a piece of 1/4 plexiglass and held it against the gaurd and slid it down below the plywood toward the table but above the path of the entering or exiting piece. The dust started to sort of cylcone and dissapeared up the dust collector hose. So I attached pieces of plexi on the front and back with toilet bolts and wing nuts that allow adjustment based on the height of the table and thickness of stock. So basically, the unit is complete with the exception of some paint that I may get to at some point.
UPDATE 10/24/2004 - I would be happy to answer any questions you may have regarding the process of building the sander. Just send me an EMAIL and I will respond as quickly as I can. Please put Drum Sander in the Subject line so my Spam Blocker won't delete your email. I now have the plan converted to an Acrobat pdf file. If you have Acrobat on your computer just click the PLAN link and print out the file. Otherwise, you can right click and save the file to your hard drive until you get a copy of Acrobat Reader installed on your computer. This was indeed an enjoyable project and a few weeks ago I completed my first tenor ukulele. I will get started on number 002 in the near future. Cheers!