Introduction: Make a Durable, Plywood Coffee Table on the ShopBot, Quick, Easy, and Cheap
My wife and I just recently moved from San Diego to Pittsburgh. We donated a lot of our furniture back in California so we wouldn't have to schlep it 3,000 miles. This left us quite coffee table-less for the past few months. No longer! I made this sturdy plywood coffee table on the CNC router table at TechShop Pittsburgh and brought it home. I'll give you the files I used and any techniques I can impart. It's not super fancy -- Frank Lloyd Wright didn't design it. It's a cheap and easy DIY coffee table. It cost me $50 to make.
Things you need:
1) Access to a CNC router table, I made this one at TechShop on the ShopBot (techshop.ws)
2) Plywood, I bought mine for $50 at a home store
3) Files, you can make them yourself in CAD and CAM software or you can use mine
2) Tung Oil
Step 1: First We Need to Draw It
To use the ShopBot to cut something out you need to draw it first. To draw this table I used Adobe Illustrator because I've used it for a long time and I know it well, but any CAD program will work. The TechShop computers all have Illustrator, CorelDRAW, and Autodesk software that you could use to draw this up.
You can download the raw .AI file I made at the link below. I left this file unfinished so you can adjust the slots to accommodate whatever size plywood you buy. The plywood I used was .74 inch thick so I had to adjust the little slots for that tolerance. This .AI file is where you do that.
This is also the file where you can adjust any sizes and lengths. Want the coffee table a little shorter? This is the file. Want the top a bit longer? This is the file. Remember, if you monkey a lot of stuff around, you need to double check that it will all fit together when you assemble it.
Step 2: Cleaning Up the .AI File to Make One Clear Cutline
After you resize the tabs and slots to fit your sheet of plywood it's time to "merge" or "crop" your pieces together. This is to make one continuous cutline. You can see what I mean by "merged and cropped" in the image above. You'll have to take all of the "raw" pieces of this table (legs, top, bottom, bars, etc.) and do this for each of them in the .AI file. It may take you a minute to think about what gets cut out and what doesn't, but this will really get you associated with the work pieces and how they fit together.
If you don't want to do that yourself, you can download my .AI file below that I've already cleaned up. However, if your plywood is any thickness other than .74 I can't guarantee that the slots and tabs will fit together. If you want to chance it, here's my .AI file.
Step 3: Running It Through the CAM Software
Next thing we need to do is send our file through VCarve. The ShopBot doesn't know Illustrator. Illustrator doesn't have toolpaths (what size router bit, or "endmill," how fast to spin the router, what direction to cut on the lines, etc) so we have to set those in VCarve. This can be a bit daunting, but a DC should be able to help you out when you get stuck.
In VCarve we're setting two (one "inside cut" and one "outside cut") profile toolpaths, adding dogbone fillets, as well as saving endmill and plywood settings. If none of this rings a bell, you'll probably want to take TechShop's "CAD/CAM VCarve Pro and Cut 3D" class. After that you should recognize what we're talking about and again a DC can get you unstuck.
Tip!: The dogbone fillet tool in VCarve is a bit funky. If you're using a .25" endmill like I did in this project, use a .125" setting in the dogbone fillet tool. For some reason the .25" dogbones come out too big --the .125" is perfect.
Tip!: Always save your toolpaths in a file that your router table knows. In my case (TechShop Pittsburgh's ShopBot) I saved it as a "ShopBot Arc (inch) w/ Speed" (an .spb) file. If you save it as a Laguna or some other proprietary file type, the table's going to jump around like a backup dancer from "Thriller."
Tip!: Use plenty of tabs. If the parts break free from each other you could injure yourself or even worse you could ruin the cut and have to go get more plywood.
So here are my files. In the .ZIP you'll find:
1) VCarve file
2) .25" endmill setting for plywood
3) ShopBot Arc (inch) w/ Speed file
Step 4: Cutting It Out!
The time has arrived! It's time to cut.
1) Set your plywood on the ShopBot table and nail it down using the plastic brads. (That's how we do it in TechShop Pittsburgh. Other TechShop's have vacuum tables or if you're using a different type of CNC router table you might use clamps or something.)
2) Put your endmill in and start your spindle.
3) Zero your axes (X, Y, and Z). Zero the Z high, couple inches off the top of your plywood at least .
4) Load your file into the ShopBot software.
5) Do an air cut (standard practice in TSPGH). Make sure nothing wild happens. Watch for any bizarre behavior now while the business end of the ShopBot is a few inches above your material.
6) Then, using the Z-zero aluminum bar, zero your Z axis TO THE TOP OF THE MATERIAL. If you're using my files as they are in this Instructable, you need to zero to the top of your ply. If you zero to the table under the plywood, the router's going to drop .25" inch into ShopBot table itself and dig a nice long trench you'll have to pay for. If you do another project on the ShopBot, you may want to zero off the table then set in your material. That's fine. But this time, using these files, zero off the top. (It's how I have it set in VCarve.)
Step 5: Bang It Together
Once you get your pieces out of the waste material of the plywood (not shown) and sanded down the rough edges a bit, you assemble the table by smacking it together with a deadblow hammer. The pieces are (if you adjusted the files for the size of your plywood sheet) made to press fit together. You theoretically won't need nails of glue or anything to hold it together. However, if you notice one of the pieces wandering around you can glue or nail it down. I didn't need to.
Step 6: Step Back. Behold. Admire Your Own Cleverness.
You have conquered the mighty oak and relegated it to holding your drinks and supporting your stinky feet as you lounge, Master or Mistress of the Universe.
Step 7: Finishing (Optional)
Here are stages of finishing. I used some old stuff I had laying around. If you don't have old stains and paints, and you want to finish it, this stage will add another $25-30 to the bill.
What you'll need:
1) Paint. Any color. You can see I used red
2) Walnut colored stain
3) Tung oil for preservation
I painted the edges red and let those dry. Sanded the flat surfaces with fine sand paper. Did two coats of walnut stain and let those dry. Then I did two coats of tung oil and used "00" steel wool between those. Let it dry and viola!