You’ve made a wonderful widget for all to enjoy. Now, where to put this breathtaking object? Well, you could put it on a shelf but that would require putting screw holes in the wall. Not an option? You could make a sculpture base! I know, it’s going to a gallery eventually and they’ll take care of that. In my experience they:
1) Don’t really have any sculpture bases. Who told you that?
2) Have bases, but they’re all being used by other artists.
3) Have bases but they are too tall/short/wide/narrow.
4) Don't have enough bases for your installation.
5) Have bases that are perfect. Unfortunately, they are also seriously mangled.
Let’s assume you’re with me and you need to build this base. How to proceed?
Step 1: Have a Good Plan
A base is likely the last thing that will come up and it often pops up unexpectedly. It’s tempting to sketch something on the back of an envelope and head to the table saw. Maybe that works for you, but I like to have a more deliberate approach. I use CAD for much of my other work so it natural for me to turn to this tool for help. Sound too involved? If you’ve ever used the parametric design features in CAD you’ll appreciate how much time this can save. Once the modeling is done, I can change the values in an excel spreadsheet and dimensions for my own custom base pop out. Cool. If you don’t already use CAD, go with the envelope. For me, it’s a huge time saver. I’ll attach Aultodesk Inventor files in case you want to give it a whirl.
I steer clear of complicated joints. I’d eliminate them altogether but some kind of simple joinery helps keep everything in place during glue-up. A rabbet joint (AKA single rabbet, overlap rabbet, *) does the job and is relatively fast and easy to cut. There are a number of ways to cut a rabbet on a panel. I prefer a table saw with a dado blade. My plan was to link to an instructable done by someone else on how to set this up but I’m not finding anything. Here’s some basic info I googled up:
* I’ve also heard these called “lap butt joints”. You’re on your own if you try and google that particular term.
Step 2: Rough Cut the Plywood
A full sheet of plywood is difficult (unsafe) to manage on a table saw. I start by rough cutting full 4X8 sheets into something more manageable – I cut them in half for this particular build. A panel saw would be nice. I didn’t have access to one this time so I used a circular saw.
Step 3: Dimension Panels
Now I run everything through the table saw to establish the overall dimensions of each piece. I’m making six bases in this build so that’s 12 side panels, 12 front/back panels, and 6 tops. I’m always careful about where I put panels after each cut. It’s easy to get confused and run something through the wrong setup. Going to the store to buy another piece of plywood will wreck your afternoon. I’m told brain surgeons go by the mantra “Slow is smooth and smooth is fast”. I try to live by that, with varying degrees of success.
Step 4: Cut the Rabbets
The rabbets only get cut on the front/back panels. Put the side panels waaay off to the side somewhere so that when you take that inevitable phone call you don’t inadvertently run the wrong panels through the saw. If you're keeping track, I'm making six bases so I've got 12 front/back panels. That's 24 rabbets to cut.
Oh, make sure you cut both rabbets on the same side of the panel, okay? You'll get another phone call in there somewhere and when you come back you'll accidentally push a panel through upside down. Much gnashing of teeth. Slow is smooth...
Step 5: Glue-up
This is where the dados pay off; they help keep everything in position when you’re gluing everything together. I like to keep a bowl of hot water and rag around so I can scrub off any glue that will inevitably squeeze out the joints. Ignore the cell phone if it rings during glueing. It’s surprising how fast things start to grab and there’s too much to loose now.
Step 6: Clamp and Nail
Clamps bring the freshly glued surfaces together and create a strong joint. Clamp everything together on one side and run down both edges with a brad nailer. The nails hold everything together while the glue dries so you can remove the clamps, flip the whole mess over, and repeat the glue/clamp/nail process on the other side.
Once you're done with the front/back/side panels you can stand the base upright and glue/nail the top on the box. No dados on the top. I always make it slightly oversized so the edge slightly overhangs (like 1/16 inch). Why the overhang? Good question. First lets move to the next step...
Step 7: Flush Trim
Building isn't perfect; there are always slight imperfections working their way into your final product. It's MUCH easier to trim the edges flush to the side of the panel once everything has dried. My design has all the dados cut 1/16 inch deeper than the thickness of the wood and the top has a 1/16 inch overhang all around. That gives you room to maneuver things during glueing without leaving too much to trim later. It's not a bad idea to run a bastard file over all the nailed edges to make sure all your brads are flush with the surface of your panels. There's always a couple brads that are slightly proud and they'll catch your router base. Once your ready, bust out the router and chuck-up a flush trim bit. These bits have a little bearing at the bottom that will follow the surface of the panel. Run this over all those 1/16 inch overhangs and you've got a perfect base.
Step 8: Chamfer
You’ve already got the router out and there’s a mess of sawdust everywhere, so why not add a little finishing touch to the base? A quarter inch chamfer give the base a finished look. It also helps prevent future damage. Sharp edges are more likely to get dinged when you’re loading and unloading for your exhibition. If you’ve never used a chamfering bit, it’s very similar to the flush trim bit used in the previous step. A little bearing at the base guides the bit along the edge of your base and creates a consistent chamfer along the edge.
Step 9: Spackle and Sand
Spackle all those little brad holes. I prefer this Dap Dry Dex because it's purple when it's wet but drys white. Putty the holes and when everything turns white sand everything flat with some 220 grit sandpaper wrapped around a flat piece of scrap. Why the block? It keeps the paper flat. If you back the paper with your hand you'll likely sand slightly below the surface of the panel. When you look along the side of the panned after it's painted you'll see little dips.
Step 10: Prime and Paint
Roll some primer on the base. Once that's dry, roll on a topcoat of flat white.and your done. Oh, keep some extra paint around so you can touch up later if someone carelessly kicks your beautiful base.