Lithopane Lamp With Rotating Shade : 10 Steps (with Pictures)

I am not new to instructables but I tend to be more of an observer of all of the great ideas rather than present one. However, once I found out about the ShopBot challenge well, how I could refuse – this is definitely one contest I am very much interested in!

The project I would like to share is a custom designed lithopane lamp with a rotating shade. To keep within the Instructables spirit, this is a project that anyone with basic wood shop tools such as: a table saw, scroll saw, router, and some basic hand tools, can complete the project. I took it a step further to show how cool a CNC router can be – and I don’t have a CNC router with near the same capabilities as a ShopBot. My router is at best a worn out, low tolerance, entry level router with a 12” x 18” table, a Rotozip for a spindle, and powered by a HobbyCNC controller. The software I use is borrowed from my work (after hours of course) and is SolidWorks for design and BobCAD-CAM for the CAM which we use for networking product design and manufacturing assembly fixtures. I am not in the wood industry but do like wood working as a hobby. Should I be fortunate enough to win the ShopBot and AutoCAD software, I would like to design and build larger woodworking pieces such as kinetic sculptures and clocks - mostly moving wooden assemblies.

Step 1: A Brief Summary of the Design

The lamp was designed to incorporate several 2D and 3D features of the CNC software. Bobart (Art package within BobCad) allows tool-paths such as V-Carving and the creation of a lithopane from a picture. Other tool-paths in Bobcad such as profiling, pocketing, and 3D profiling are also used in this design but as mentioned prevously, the basic lamp can be made without a CNC router.

The lamp uses a fixed base and the lamp shade rotates slowly about the base so the pictures can be easily viewed. I am expecting a full rotation in ~3 minutes using a motor with gearhead running a 6 RPM and then geared down with wooden gears to approximately a 16 : 1 ratio.

I have provided full size drawings for all parts although some drawings may be too large for a standard printer so either you will need to have them printed at your local print shop, print several sheets and tape them together, or scale them and work off the dimensions. All the drawings are at the end of this Instructable along with a STEP file of the entire assembly that can be imported into most 3D CAD software.

The wood chosen for this project is fir – that’s right, 2x8” and 2x10” building lumber. Depending on where you would like to display the lamp, the variety of woods are plentiful. The cheaper softwoods like fir, knotty pine, and cedar work well with a country or rustic look. Poplar and clear pine are also good choices at a slightly higher cost and the more premium woods such as oak and walnut and exotics can also be used if elegance is what you are after. Given the amount of time you spend in the workshop, don’t let the initial cost scare you especially if the wood is correct for the setting.

Since I have a planer, any material thickness can be achieved however, all of the parts for this project are made from either ½” and ¾” thickness and these thicknesses are available for a few species at your local home improvement store. As an alternate, plywood can also be used and comes in ½” and ¾” thicknesses and is veneered with a fir, oak, birch, and others and is a more stable building material than solid woods so this may also be the better option for some of you. If you use plywood, the assembled lamp shows very few cut edges and these can be hidden using veener edging.

Step 2: Top Cover

The cover is made by laminating 4 pieces of 2x8 lumber. The lumber is glued and clamped making one large piece of material. When dried, I cut the lumber to an oversized length and width and planed it down to 2 ¾” tall. This thickness is not critical and is a result of the maximum z-height my CNC router could handle.

I designed the top cover to incorporate fan blades which I thought would be cool to give the impression that the spinning was the result of the heat produced by the light. In reality, the cover can be solid or have a 2D spoke type pattern made using a scroll saw letting the light out and creating shadows in the room as it rotates. The critical dimensions (so to speak) are the outer dimensions as shown on the drawing. The major difference that you may want to incorporate assuming you do not have a method to make a pocket is the ¼” wall thickness around the perimeter of the bottom of the part. For this, you will have the option to assemble the top cover directly to the top of the lithopane frames and place trim molding cut out in the arc shape if desired. The top cover is not a structural member of the lithopane frames so don’t be worried if you choose a simple install.

To add a rounded look to the top cover, use a hand plane and sander to shape the wood.

Step 3: Lithopane Frames

There are 5 lithopane frames and you do not need to create a lithopane to make your lamp. The intent of the frame it to hold a translucent/diffuser material to let the light out. My frames are made for 2x10 fir planned down to ¾” thick. The lumber is cut to length and on your table saw, cut a 36 degree angle on each side. To make the elliptical opening, print off the drawing and adhere it to the wood surface and use your scroll saw or similar to follow the line and try to make all 5 frames the same. Use a ½” round over router bit to create the rounded surface of the ellipse. To make the pocket on the back side, you can remove the material with your router using a flat bit and an edge guide. If you do not have an edge guide, there is enough clearance to mount the diffuser material directly to the back of the frame.

I added a step which incorporates some basic V-carving on the frame to give it more decoration. V-carving is different from engraving where you use a 60 or 90 degree bit (typically) and the v-carving software will add more depth to pocket areas and less depth to line areas. The 'picture' is a vector file, usually a .dxf. If you have the skills and don’t have a CNC router, you can try carving or wood burning those areas to create a decorative look but this is certainly not required.

Step 4: Frame Support and Gear Train Mount

The frame support (2 pcs) is the structure that helps hold the frames together and provides an accurate angle. These have the same outside spacing as the inside spacing of the frames when fully assembled. Use your table saw to cut the 5 edges and your scroll saw to cut out the circle.

The motor and gear mount is cut from a flat sheet and is mounted on 2 small rectangle posts. The outer dimensions of the mount are not critical however, the hole relationship is as these locate the gears to each other. The rectangle posts are intended to be small to keep the internal shadows of the lamp to a minimum.

Step 5: Gears

To keep it simple, I assigned 3 large gears and 3 small gears all with the same number of teeth and size. The large gear is a 15 tooth and the small gear is a 6 tooth. The ratio for the entire gear train beginning at the motor is 15.65 rotations of the motor to 1 rotation of the lamp shade. The actual ratio and speed at which the lamp rotates is not critical. I simply wanted the lamp to rotate slowly so that you can view the pictures without being distracted by a fast spinning motion.

Print off the drawing for both gears and adhere it to ½” thick wood material. Plywood is better than solid woods for making gears with a scroll saw and Baltic birch is least likely to chip. With a CNC router, this is less of an issue. I have found that wooden gears can be easily cut in a variety of wood materials using a 2 flute ball nose end mill with small depth steps ~0.040” per pass. A finish pass is not needed (or wanted) as the finish pass will end-up chipping the gear teeth due to the minimal retention of wood grain supporting structure.

Note: that I placed a 1/2" diameter plastic insert into 5 of the 6 gears. One of the 6 tooth gears uses a 3/16 hole size so it can be friction fit on the 5mm motor shaft. All others use bolts as an axle.

Step 6: Lithopanes and Light Shades

My lithopanes were created using a feature in BobArt where a picture is imported and BobArt converts that picture into a 3D model. Sound simple?- it actually is. As with everything, better results can be had by importing the picture into photoshop or similar and cleaning it up a bit. The 3D features are based on colors which represent the height, white being the lowest feature and black being the highest feature (when light shines through the translucent material, it passes more easily at the thinnest features and is blocked more by the thickest features creating the depth illusion).

For my lithopanes, I chose 0.236" translucent white polycarbonate. I am told that the best material to use is Corian, since it is more rigid and has a higher melting tempature than plastic. Unfortunately, Corian in the sizes I wanted is expensive and hard to find. The 'photos' I used are shown in the pics below which I found on-line and cropped them using the oval shape of the Litho Frame opening. Of course they can be actual photos as well, these were someone's paintings but they were of the approximate shape I needed.

To machine polycarbonate, I used a 0.062" carbide ball-mill and programmed a rough cut set to a maximum machining depth at 0.130" with a 0.02" stepover and a 45 degree zig-zag angle across the material. Using the same bit, I set the finish at a maximum depth of 0.160" with a 0.010" stepover and a 45 degree zig-zag across the material. To give the litho a finished look, I engraved an oval around the picture using a 1/4" ball-mill, 0.170" deep. Just as an FYI, several software brands are available that can do lithopanes. One of the cheaper 'stand alone' programs is made by Vectric called "PhotoVCarve". You can download a demo and try it for yourself. Even if you don't have a cnc router, it will display an image representing the final machined part.
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Step 7: Spindle, Base, Trim, and Mount Support

The spindle can be made or bought. I found my spindle in the Curtain rod section of the hardware store and there are many to choose from, especially if you plan to paint your lamp since several are plastic and intended to be painted to match a home.

The other parts are simple and hopefully self explanatory. Nothing special here. Please refer to the pictures below and the drawing to review the dimensions and other details.

Step 8: Assembly Summary and Tips

To add a few pointers:

Pre-sand all your parts.

Lamp Shade:
I used wood glue primarily to hold the parts together. When required, I also used brads to help aid in the assembly of the 5 pieces to keep them in place. 2 straps were also used to go around the entire shade to hold everything tight. If your lamp frame part is not a perfect fit cut it to size accordingly. The frame will assist in making sure all 5 sides are the same instead of relying on the mitered anges from each litho frame. Once the glue is dry, attach the trim molding around the bottom of the shade. The top-cap can also be glued to the top of the shade. - The spindle can now be installed to the top-cap. Install the lithopanes or diffuser material in the recess of the litho frame and secure with a small bead of hot glue.

Gear Train:
The gear train assembly may look complicated but it is relatively straight forward assuming you cut out the gear moount correctly, every thing should line-up. To begin, press in the 1/2" plastic spacer into the 1/2" center holes in 5 of the 6 gears. The sixth gear should have a 3/16" hole to press onto the motor. Glue one 6 tooth gear to one15tooth gear so you will have two gears joined together. In the picture below showing the bolts thru 2 gears, the bolts are only used to keep the gears concentric.

The bolts for the gear train are to be used with washers and held in place on the opposite side with a washer and nut. The height of the seconday nuts (and washers) that stand off the gears should be approximatly 1/2" apart but you can easily adjust as needed. these are in place so the gears do not rub against each other while turning.

Base assembly:
Attach the 'mount suppor't parts to the base using the #8 wood screws. Once secure, remove the gears from the 'gear train mount' and attach the 'gear train mount' to the opposite end of the 'mount supports' using the same type of screws. replace the gears and if you have not done so yet, apply the friction gasket to the top most gear using a spray adhesive.

Wiring:
The electrical design is to use a lamp power cord with a rotating switch or similar and wire both the light bulb housing and the wall wart to the power cord, this way both the light bulb will light and the lamp will rotate without the need for separate switches or 2 power cords going to the lamp. Install the lamp hardware and secure the bulb socket to the top. Feed the wire thru the extension and attach another short wire that will go to the wall wart. The bulb socket should have screw terminals where both wires will attach. The wire to the wall wart will need to be soldered to the terminals. The wire from the wall wart can be secured to one of the mount supports and hot glued at a few places to keep the wire secure. Cut the wire to the proper length and solder to the motor. The motor can run forward or backwards so decide which direction you want the shade to spin. Ensure both lamp, motor and switch works.

Choosing the right finish:
Hardwoods accept transparant stains better than softwoods whereas softwoods look better natural or painted - maybe a solid stain or whitewash. For this lamp, I chose to keep it natural and used a wax with orange oil (found in the staining section of the hardwood store).

Almost done:
The lamp shade can now be installed onto the base. You may need to balance your shade - do so by placing nuts or bolts on the inside frame support next to the diffusers. Enjoy.