Introduction: Plywood Sphere Table
I was asked by my parents to make a new table for the living room for my school product design project, they specifically asked for a table which was modern, quirky, stylish and had to be made using plywood as a feature. I never thought I could use ply as a feature for a table, but after an enormous amount of coursework and countless designs; I found the perfect use for plywood in a great looking table which has now become the centerpiece of our living room.
I decided I would share my method with you guys so that you could make your own :), (without all the folder-work and documenting!)
You Will Need...
- 1 x Sheet of plywood - (6'x8'x12mm)
- Table surface wood of your choice - I used Ash (you need enough to make a 650mm circle) So 3 pieces (700mmx250mmx32mm)
- Wooden dowel - (1 1/2", 40mm)
- Wood glue - (Or PVA)
- Danish oil - Used for finishing
- Biscuits - "Flat dowels" not actual biscuits!!
- Band saw - Preferably with a thin blade. A band saw will make it much easier to cut out the ply circles
- Band saw circle cutting attachment - This is very handy, it allows you to cut quick circles on the band saw easily, its not a must
- Jigsaw - Yes its a type of saw
- Pillar drill - A handheld drill will suffice
- Spade bit - (1 1/2", 40mm)
- Sand paper - A selection of grits
- Biscuit cutter
- G clamps
- Protractor, compass, ruler, pencil etc., the usual stuff...
The total cost to build this table was around £20. I do not own most of these tools so I used the machinery and tools provided by my school. I have created various documents and templates to assist with the project along the way, these can be downloaded by just clicking on the PDF icon at each step.
Step 1: Measuring and Cutting Rings
The leg of the table consists of a total 68 circles which make up 6 spheres, I have created a PDF with a table which shows the ID number and Diameter (in CM) of each of the circles needed to make the leg spheres. In order to save weight and reduce cost, the spheres are semi-hollow; each sphere has a solid center core which acts as the main support of the leg, and hollow rings in the outer layers build up to make a spherical shape.
See the "Circles layout" PDF I have included in this step, this shows you how to arrange the circles on the plywood, the tables show the diameters of each circle in CM. The circles have been arranged within each other where possible to save wood, as far as I know this is the most efficient way of cutting a sphere of plywood. Use a compass and pencil to draw the circles onto the wood, placing them closer together will reduce wastage. Make sure to add the ID number on shown on the layout file so you can assemble them easier in the next step, and mark a center point for later. When all circles have been drawn onto the wood, use a jigsaw to cut roughly around each cluster of circles.
Using the band saw, cut around the outer circle line on the plywood, this will need to be done for each piece. Once you have all clusters of circles cut on the outside edge, make two cuts from any point on the outside circle to about 1cm from the center point and cut out the piece in between; the two lines must be at minimum your band-saw length apart, see image above^^. This slot will allow the band-saw blade to be placed within the circle in order to cut each ring out, it also adds a unique spiral feature when we glue the pieces together later. Attach your circular cutting jig to your cutting bed. ( If you don't have a jig you will have to do the next part by hand )
Place the plywood into the jig with the center point lined up with the spinning clamp on the jig. Tighten the clamp so that the circle is held around the center point, this will be its axis of rotation when cutting. Align the edge of each circle with the band saw and turn it on, make sure to be wearing goggles and have a safety guard down on the saw. When pushing the plywood through the blade, the band saw jig will rotate around the center point creating a perfectly cut circle. If you do not have a band saw circle jig don't worry, circles are just as easy to cut by hand, but may take a while longer.
Repeat this process with all further rings of plywood. You should now have a total of 68 circles with a slot in them (they'll look a bit like a C), these will make up 4 spheres and 2 hemispheres. You can now stack the pieces of wood in alphabetical order and get a rough estimate of what the final table will look like! That's the most tedious bit over, next we need to glue the pieces together...
Step 2: Gluing the Rings Together
Now that you have cut all the rings out of plywood, they can be glued. It's a good idea to do a dry fit to see how they all fit together, each sphere/hemisphere is numbered 1-6 (from bottom to top) and each segment is in alphabetical order; this is the order in which they must be stacked to form a sphere. There should be an overlap of at least 12mm around the edge between each layer.
When gluing the pieces together, it is important to not line up the slots in each piece, doing so will affect the structural integrity of the spheres and they may fall apart. Placing the slots in a spun pattern creates an interesting spiral on each sphere, this also makes them stronger. Start by adding a small drizzle of wood glue to the edge of the rings (remember they each overlap by 12mm). spread the glue around the wood so it covers the edge and align the piece in the center of the next piece so that the slot is rotated around an inch from the previous slot (see image). Continue this process on all pieces except the solid center pieces, add glue to the whole surface of these pieces so they are stuck firmly together.
It is best to glue half a sphere at a time so they do not slide out of place. Clamp the pieces together using a G clamp and leave to dry overnight.
When the hemispheres have completely dried, draw a straight line across the underside of the solid circle, use the band saw to cut the whole hemisphere in half across this line, you may want to turn it up side down to get a better cut. WARNING this is quite dangerous as you may need the full height of the band saw blade to be visible and you may have to remove the safety guard, take your time on this as you do not want to break the blade, its cutting a lot of wood at once. If you prefer using a safer method you can cut the piece by hand but this will take a long time and may not be accurate. Once cut, the two half-semicircles can be flipped and glued in the opposite direction so that the plywood circles are now laying perpendicular to the flat edge.
Step 3: Fixing the Leg Together
The spheres are fixed together using thick wooden dowel. The angles of the dowels are shown in the image above. Using a protractor, measure these angles onto the wood and make a mark for where to drill a hole for the dowels. With a spade bit in your drill, drill a hole 8cm, 3 1/4" into the wood, whilst drilling, point the drill towards the center of each sphere to keep aligned. Make sure you are drilling into the center of the solid four layers of wood in each sphere. You might want to over compensate on the angles when you drill the last hole, try to make it slightly steep so when finished the weight of the table will pull the leg into shape and you will have a level surface.
Cut 5 lengths of dowel 16cm, 6 1/2", using a handsaw, cut small grooves into the dowel randomly, this will leave space for the glue and prevent twisting later. pour a small amount of glue into the hole and spread a thinner layer onto half of the dowel, press the dowel into the hole and using a small mallet, gently tap the dowel into the wood until you feel it has hit the bottom. Glue all the spheres together in this manner EXCEPT for the top hemisphere (No.6), this piece will be fitted to the table top before it is glued to the rest of the leg (it will make life easier this way) After gluing each of the pieces together add a weight yo the top piece so that that it dries in place. I used a few G clamps stacked on top of each other. Leave to dry for a couple of days just to be sure the glue has completely dried, in the mean time we can start on the table top...
Step 4: The Table Top
Typically, you can buy hardwood in long lengths in 300mm widths. For this project you will need 3 pieces, 700mmx250mmx32mm. These pieces will make up a 650mm circle when we join them together. If your wood is not already pre-planed, you will need to do this by hand, plane the sides, top and bottom of the wood to a roughly flat layer so it is easy to work with, the sides of the wood need to be particularly planed well as they will fit together, use a ruler to mark a line which you can plane to, and keep checking your surface is as flat as possible. If you lay out the 3 pieces so they are touching there should not be any gaps between them, the flatter you plane the sides, the better quality your table top. Once you are satisfied with your planing, it's time for biscuit cutting.
Lay the pieces out again and mark lines where you will want to place biscuits, draw a line across the pieces so they can be lined up again later, you may want to note the top or bottom too. Note that the shape will eventually be circular so you may need to account for this in your biscuit positioning, see image^^. Align the biscuit cutter so that the blade is centered in the middle of the wood, choose the depth setting on your cutter which matches the biscuits size number and cut each place where you have marked a line for a biscuit.
To glue the pieces together, simply drizzle some wood glue into the biscuit hole on each side and insert the biscuit, cover the rest of the face with a thin layer of glue wherever the wood will come in contact. Press the pieces together and clamp them firmly in place, clean up any glue that is pushed out and leave for two days. It is best to glue each piece of wood separately so you achieve the best results.
Once dry, remove the clamps from the wood, you should now have 1 large piece of wood, time to make it into a circle. If you do not have a compass large enough to draw a 650mm circle, you can easily make one from a scrap of long wood with a couple holes drilled in. Mark the center of your piece with an X in pencil, and draw one large circle of radius 325mm. Take this to the band was and slowly cut around this line, careful not to burn the wood by going too fast. Next, use the plain to go over all the surfaces of the table top, make the table as flat and even as possible on both sides.
After planing is complete the top hemisphere we saved from earlier can be fixed to the underside of the table top, pick the side of the wood which looks the least aesthetically pleasing and mark an X in its center, place the hemisphere atop the piece lined with the middle as much as possible. Hold the hemisphere firmly in place while marking the center of the top and bottom (in the direction of the plywood's grain). Remove the ply and measure 8cm from the marks towards the center of the table top, align your biscuit cutter perpendicularly to these points and cut a hole for a biscuit. Mare 8cm from the top and bottom of the hemisphere and do the same, you can do a test fit by sitting biscuits in the slots and putting the pieces together. Glue the hemisphere to the table top with the biscuits in place as we did earlier and leave to dry overnight.
Step 5: Finishing
Finishing is the mist fun part of the process, the plywood spheres will not need sanding as plywood has its own rough laminated finish, these can be left for now. Begin with a high grit sandpaper and sand the surface of the table, here you can round the sharp cut edges left by the band saw and clean up the sides circle if you had a messy cut. It is always best to give the underside of the tabletop a good sanding too (you only need to use a high grit for this). After you are satisfied with the flatness of the table top, move to a lower grit sandpaper, take your time and sand all over the top, the table should start to feel really smooth now. The longer you spend sanding, the better quality your table top will be.
Once sanding is complete, wood finishing oil can be applied to the wood, I chose danish oil because I like the slight dark tone it adds to the wood. Pour a small amount of oil onto a plate and using a piece of rag or cloth, rub the oil into the wood, do not go overboard with the oil as it may not all soak in and your table will begin to look shiny and wet. In small quantities firmly massage the oil into the wood,leave to soak in for a few minutes and repeat. Oil works particularly well on the cut edge of the plywood as it brings out all the colours in each layer. Give 3-4 coats of oil to the entire table (leg and top) until you are satisfied with the finish you have applied. The more layers of oil you apply, the darker the wood become and the more colours of wood will show, everyone has their preference of wood tone so see how many coats work best for you.
Finally, the table top and hemisphere can be glued into the sphere on the leg using the last piece of dowel and leave to dry overnight just as the previous step.
Congratulations! You have successfully finished making the table. This table is by far not strong enough for a person to sit on, but is more than strong enough to hold a vase, lamp, flower or drinks; it may hold whatever you so desire (as long as it is reasonably light).
Thank you for reading my Instructable, I hope you can take some ideas from my table or maybe make your own. I'd love to answer any questions you have, let me know if you make one of these tables or have any ideas on how I could improve my design, just leave a comment below.