Making a Plastic Composite Coffee Table
Coffee Table no. 1298 - The Finished Product
How I made a plastic composite Coffee Table
The following hubpage illustrates the steps I used to make a custom coffee table. I've tried to make it as informative as possible so anyone interested (or with enough time) can make one themselves.
The first step was to design the overall shape and hole pattern. I did the design layout in Adobe Illustrator. There are a total of 1298 holes (hence the name) which create the circular pattern on the top of the table. The shape is a modified rectangle, drawing inspiration from old-style Television sets and grainy pixelated resolution.
A free copy of the Illustrator file I created is available for download. If you have fairly new version of Illustrator for your computer, click here to download the .ai file.
I did not have access to a large bed CNC machine for the drilling, so I had to drill every hole myself. I had the design template printed out, full scale, on a large format printer at Kinko's. I then glued this printout onto a 3/4" thick piece of plexiglas that had been cut to size.
Drilling the Holes
Each of the 1298 holes had to be:
1. Center punched - this allows the drill point to find the center of the hole and not wander.
2. Drilled with a combination drill/countersink drill bit - this drill bit forms the larger, tapered counter-bore which will eventually be visible from the top of the table.
3. Drilled through with a 1/4" drill bit - after the combination drilling is done, the rest of the hole is cleared out with the 1/4" drill bit. Note: try to find a drill bit made specifically for plastics. This will help, especially when the bit breaks through the bottom of the plastic, preventing grabbing and tear-out.
So, in actuality, I had to mark the 1298 holes and then drill 2596 holes. It took me about a week and by the end, I was nearly going insane. If you are willing to try this, you might want to find a friend with a shop bot or some sort of CNC controlled machine to do the drilling.
After all the drilling was complete, I removed the protective paper from both sides of the drilled plexiglas and cleaned the plexiglas thoroughly. Compressed air works very well to blow out all the holes of remaining plastic bits and pieces. I cleaned both sides of the plexiglas with detergent and from there on only touched the plastic while wearing gloves.
Note: Oil and dirt from your hands and surroundings can interfere or inhibit the curing of the polyester resin.
Build the Mold Box
I used 3/4" melamine covered particle board to create my mold box, making sure the inside dimensions of the box were the exact dimensions of the drilled plexiglas piece. Before placing the plexiglas sheet into the box, make sure to heavily coat the inside of the box with a mold release agent. I used a silicone based spray to coat all the inside faces of the box. This step is critical and will greatly help the release of the cured resin from the mold box.
Mixing and Pouring the Resin
Mixing the resin is a key step. I used a Polyester Resin and color pigments purchased from Tapp Plastics. If you can afford it, I would highly suggest using an Epoxy resin instead. Polyester resins STINK really bad and also shrink quite a bit when they cure. The shrinkage can lead to cracking and inconsistent results. Epoxy resin has a much lower shrink factor, hardly stinks at all, but is MUCH more expensive. I also added a wax curing agent to the resin to seal the open surface of wet resin from air exposure. Since my mold box was open on one side, the exposed resin needed to be sealed off from air to help cure. The wax floats to the top of the poured resin and forms a membrane. This membrane prevents air from interacting with the resin and retarding the curing cycle. If you are going to use polyester resin, MAKE SURE to mix and cure the resin in an EXTREMELY well ventilated area. This is bad stuff and you don't want to breath it in or expose yourself to it for very long.
When mixing the resin, it is a good idea to use some sort of squirrel mixer to help speed up the mix and consistency. Add the pigment slowly and carefully to the resin, following the manufacturers instructions. Note: it is a good idea to add the pigments and fine tune the color before adding the curing agent (or part "B" of the resin mix). This gives you more time to before the curing cycle begins.
After mixing, bang the bucket many times on a hard floor to release any air bubbles that have been trapped inside the resin.
Pour the resin nice and slow to prevent any new air bubbles or pockets from forming. I let the resin flow all over the plexiglass sheet. Gravity will pull the resin down into all of the drilled holes. I helped push as much resin into the holes by sliding a plastic squeegee back and forth over the plexiglass sheet.
Cleanup and Sanding
After a full 24-48 hours of curing, I pulled the newly made plastic composite tabletop from the mold box and started the cleanup process. Resin had flowed everywhere and had to be removed and sanded away from both top and bottom sides of the tabletop. By using chisels, scrapers, files, and a portable belt sander, I got the tabletop to the rectangular condition as seen to the right. This cleanup step took about 2-3 days to complete.
Note: Again, it is very important to do this kind of work in a well ventilated area. Always wear a dust mask or respirator and wear eye protection as well. The sanded polyester resin powder is finer than flour and can easily get in your eyes, or even worse, lungs. Take care and be patient.
Cut to shape
Using the same Illustrator file as above, I printed out a second copy and used the outline to trace the final shape onto the rectangular tabletop. I used a vertical woodworking band-saw to cut away the outer shape of the table. After cutting, there were still band saw marks on the edges. I cleaned the cut marks with more sanding and filing. I then rounded all the edges, both top and bottom, with a 1/4" roundover bit with a hand router.
The next step in the finishing process is sanding and polishing. I progressively sanded the tabletop with sandpaper grits, starting at 180grit all the way up to 6000. I did most of the sanding with an electric palm sander and some portions by hand. The 1000-6000 grit papers are best used with water (wet sanding) and create a true glass, polished appearance. You can usually find the high grit sandpaper at automotive/autobody stores.
Note: the polyester resin is much softer than plexiglas and will sand down much faster. Use care when sanding to keep the resin layer flush and even with the plexiglas.
Forging the legs
The final step with the coffee table was creating the legs. I used 3/8" stainless steel rod to form the legs. This thickness offers plenty of strength and gives a lightweight yet solid visual appearance.
Making the Steel Legs
To create the forged legs, I tack welded several guide pieces down to a metal table to form a jig. I clamped the beginning of the rod to the top left edge of the jig. With an oxy/acetyl torch, I heated certain areas of the steel bar till red hot and bent and clamped them to the jig form. I started from one end of the jig and heated, bent, and clamped the bar until I was at the other end, creating a complete leg piece. Once completed, I cut the remaining bar off, sanded off the torch marks, and drilled and tapped holes for the tabletop hardware.
I assembled the legs to the tabletop using 1/4"-20 stainless steel screws. That's it!
If you are interested in some other projects I have worked on, you can see my portfolio here. Let me know if you have any questions, comments, or suggestions.