How to design and fabricate a coffee table made out of coffee.
Step 1: Design of a Coffee Table Made From Coffee Part 1
So what does a coffee table made out of coffee look like? This is a very interesting question in that we don't really have anything to compare it to. There are plenty of designs for coffee tables, but no precedents for using coffee as a material. I began by breaking down the necessary elements for a coffee table; a top surface for placing cups and objects as well as legs to hold up this surface. In order to challenge myself, and to rethink the form and function of the traditional coffee table, I chose the form of rectangular surface with only three legs. The least and essential number of legs to hold the table surface. I chose a typical size for the table, 42" wide by 18" deep and 16"-18" tall. In this fashion, the coffee table would still be recognizable for what it is. As well as function properly. In order to challenge myself, and to rethink the form and function of the traditional coffee table, I chose the form of rectangular surface with only three legs. The least and essential number of legs to hold the table surface.
To achieve the challenge of three legs, I 3D printed couple iterations to see which configuration was most stable and aesthetically pleasing. Using three legs, I noticed that staggering them long wise seemed to be most stable and so I chose this configuration with a wider stance and 15 degree legs.
Step 2: Design of a Coffee Table Made From Coffee Part 2
Next came the task of figuring out the form of the top surface and the legs.
I wanted to play with the relationship between the surface and legs. I noticed by looking at coffee tables that we often don't see their underside and wanted to find a formal tension between what is underneath and above. In this sense, I imagined a surface in which the legs would try to reveal themselves by leaving their imprints on the top surface. I set out to make a Grasshopper script which divided the surface into a series of lines, and then displaced them based upon a point of my choosing - a point which represented each leg hidden underneath. The point would then displace each line in its area of attraction in all directions (X, Y and Z) based upon its vicinity to the line. The lines where then piped, using a marching cubes script, to recreate the table surface.
The legs largely resulted from a structural necessity in form. I had already identified the location of each leg and angle which best supported the table surface, so the rest was mostly a result of the process.I made another Grasshopper script which took the area of attraction around each point and lofted it to the floor in a series of rotated and scaled sequences. The result was a form which looked as though the objects on the surface above were pulled down through the table surface on to the floor in a firmly supported fashion. Thus achieving a formal language and relationship between the legs and surface of the coffee table.
Step 3: Casting Used Coffee Grounds
Casting used coffee ground is a process which is actually harder than it appears. It is important to take into consideration factors such as grounds vs. casting medium ratio, moisture of grounds, size of grounds, form work, thickness of cast, etc.
For my mixture I use a casting resin, 7132 Resin and 2001 Hardener, from a local arts supply called Douglass and Sturgess, but most two part Epoxy Resins will work well. As a note, I prefer using Epoxy Resins rather than Polyester Resins to avoid the smell as well as for the increased strength. The ratio of coffee grounds to resin is extremely important - I would suggest using a 60% coffee ground to 40% percent resin ratio by weight. The resultant mixture should be gooey like fudge and still be able to compact and set when adding vibration. It is also important to use dry grounds otherwise the moisture within the grounds will interfere with the resin as it cures.
Next, it is important to use form work that the resin will not adhere to. Try and avoid porous materials such as wood and foam. I find it works best If you can line your form work with acrylic and apply a simple mold release. Otherwise using Minwax or any other sort of Butchers wax to seal wood also seems to work well, however it can leave imprints on the cast. I designed my form work to only cast as little material as possible and to allow for pours that were 2"-3" thick at a time. This meant building cavities to displace areas which would only add significant time to my CNC milling time and waste material. Keep in mind the more space you have to cast, the more Resin you inevitably need to mix, and the more expensive your casting will be.
Step 4: Milling Used Coffee Grounds
This was the fun part! Milling took a total of two days - about 7 hours for the top and 6 hours for the bottom - and used a method of flip milling to completely cut the stock coffee ground material. This involved fabricating a base to hold each face of the stock material. I planned on this before hand and organized my casting/milling process so that I would have standard and regular depths to hold my stock material for each side. I simply screwed some 2x4s and other standard lumber, to frame out and secure my stock, into a spoiler board and clamped that to the bed of the 5 Axis DMS router at Autodesk's Pier 9.
After the first side was finished milling I took another spoiler board, framed up in a similar fashion as my first board to hold the stock, and placed it on top of my piece. This meant my piece was sandwich between both framed up spoiler boards so that all I had to do was apply some pressure with a clamp while I literally flipped the sandwiched assembly. As mentioned before, the spoiler board was framed up to support my stock material so now what was sandwhich on top became my new fixture to support my stock material and mill the other side.
Over all milling went well, the router cuts through the mixture of used coffee grounds and resin like butter. It left the room smelling like coffee! Also, its important to save the left over chips as this is great material to cast again.
Step 5: Finishing Used Coffee Grounds
Once the stock material was milled on each side, the coffee coffee table top was fabricated and ready. However like most materials, there was still plenty of post processing and finishing to properly seal and make sure the material has a beautiful finish.
I started off by mixing a small batch of left over coffee chips from the milling process with some resin to patch in any small cracks or holes. I then brushed on a light layer of resin to let set and fill in any micro cracks. Once this was dry, I then took a sander and used a 100 grit to finish flush and imperfections or bumps created from the previous layer of resin used for finishing. I then applied an even lighter coat of resin, just to wet the surface, and let the coffee material really pop! Next I flipped the piece over, using my previous spoiler board fixture sandwiching technique and repeated the same process on the opposite side.
Step 6: 3D Printing Used Coffee Grounds
Perhaps one of the most interesting and difficult applications in reuse of coffee grounds, 3D powder printing is a process which works great for fabrication. I previously mentioned this process in another instructable “How to Reuse Your Old Coffee Grounds for Fabrication”, so I won’t go into the details but please check it out to learn more! This application of 3D printing was slightly different in that instead of creating a panelized structure, I wanted to make each leg as a 3D printed element.
The hard part was fitting each leg inside the build bed of the printer. The leg was about 14” long and my build bed dimensions are 8”x8”x10” which meant I needed to print each leg as two separate parts. I decided to logically break up each leg into the upper half, which had more curvature and help distribute the loads from the table downward, and the lower half or “feet”, which are a straight run making contact with the floor. I carefully modeled out a basic mortis and tenon which followed the curvature of each plane where I sectioned the feet off. Additionally I made the upper half of the leg hollow, with a ribbed structure, and tested out some new grasshopper scripts I found in making lattice structures to cut down on material consumption while still maintaining structure in the lower half of the leg.
After the prints were done, I applied a layer of resin for finishing and used some super strong fast drying epoxies I found at my local hardware store to glue the mortise and tenon together. Once the legs were assembled, I repeated the process to attach them onto the CNC routed table surface. And voila! A Coffee Coffee Table.