# How to Build a Cafe-Wall Illusion Coffee Table

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I wanted to see what I could pull off in the way of illusions, with fairly simple carpentry techniques. After some research, I settled on the cafe-wall illusion. With a repeating pattern of light and dark squares (yes, they are squares- all angles are 90 degrees), the illusion of bending appears.

I never think my projects are going to be interesting, so I don't take mid-project pictures. So I apologize if my intermediate steps are unclear due to lack of pictures. Feel free to drop me a line and I'll try to explain what I did in more detail.

I've entered this project to the Epilog contest, so please vote for me if you think I deserve it. As a university student, I'd probably drag it on-campus, and set it up to allow other students to use it for free/at cost for their projects, personal and professional. I know I've got a whole bunch of ideas I've been sitting on without the extra cash to burn on laser/CNC cutting; I'm sure others here do too.

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## Step 1: How It Works

The basis of this pattern is rows of alternating light and dark squares, each offset by about 1/2 square from the next. The rows alternate back and forth- forward two steps, backward two steps, repeat.

Also, a key aspect is an intermediate color (in my case, grey-ish) in between the squares.

## Step 2: What You Need

Materials:

For this table, I used three different woods. You can use whatever you want, but you need two with significantly different colors, and a third that is in-between. In my case, I went with white-black-grey. To get this, I used:
• (Black) Walnut
• Hard (White) Maple
• Ash (grey- I wandered the lumberyard and picked the grey-est board I could find)
• 1/4" MDF sheet, somewhat larger than the ultimately desired shape
I exclusively used 4/4 lumber (that's actually around 2 cm thick, for you non-americans), although some thicker wood would have been nice for the legs- I just laminated two pieces for those.

Tools:

I made every cut on my table saw, using a fence and a cross-cut sled (I won't go into all the details of how to make one-it's fairly self explanatory, and you can always look elsewhere for details). You can probably use a chop/miter saw instead of a cross-cut sled, but you'll still need a tablesaw to rip your boards into the right width. Given all the cuts you'll be making, I strongly advise you avoid hand-tools here.

You'll want a modest pile of woodworking clamps, as well as a pair of nice straight-edges to clamp across the whole row. A nice straight board will do well- I'd recommend giving it a layer of furniture wax to keep it from getting accidentally glued to the workpiece. you can always remove it later if you want to use the board in something.

If you don't have access to the power tools, you might be able to get someone to do the cuts for you; I think many woodworking stores (like the one I go to) have shops for doing custom jobs. If you're just getting started in woodworking, have no fear; this project is about as simple as things come- it's just lots of repetition. There's no fancy cuts anywhere.

## Step 3: Make Your Cuts!

I went with squares about 2 inches on a side; the size isn't critical. Clean up the sides (get rid of rough edges, ensure all sides are 90o from each-other), and rip all the walnut and maple boards to the width you've chosen. Also cut the ash boards into thin strips, maybe 1/8"-3/16" or so (I didn't really experiment here- just eyeballed something that seemed right relative to the size of the squares). You'll need several long strips of the intermediate wood, and lots of short ones, so make sure you've got enough.

Once everything is cut to the right width, set up your crosscut sled or miter saw with a stop so you can easily cut all your boards to the right length. Once you hit a rhythm, you should be able to churn out squares very fast- I also stacked the ash strips to cut them 3 or 4 at a time, although I don't know if that would work on a chop saw.

## Step 4: Glue It Up.

I tried to just glue them to eachother, but that failed miserably. So I used a thin sheet of MDF as a bottom, and glued them down to it, and to each-other. Lay up one row at a time, remembering to intersperse the thin spacing strips. Once the layer is completed, add a long strip on the side.

Then clamp it all together. I had the whole thing up against my tablesaw fence (nice and straight!), with a long straight-edge clamping against it. I had one long clamp across the whole row, and another straightedge across the top, clamping down the row. I allowed each row to set-up before I added the next one.

You'll have rows starting and stopping in different places; just make sure the surface is at least as big (or bigger) in every dimension as you want.

## Step 5: Clean Up the Tabletop, Fashion It Into a Table.

Once you've finished all the layers you want, put it back into the tablesaw. Trim the long edge(s) (you should have mdf overhanging on three sides if you went with my layup scheme). The short edges are a bit trickier- luckily, my tabletop just barely fit into the crosscut sled.

From here, you can go anywhere with this. I had initially planned to use it as a jumbo cutting board, but nixed that idea (confusing optical illusions, sharp knives, and fingers didn't seem like a good combination).

My minimalist coffee table is quite simple: I took some extra 2" wide maple, and dado'ed it lengthwise so the tabletop would fit snuggly inside. I made 4 pieces of this maple, for each side. For the legs, I took four pairs of 1-3/4" walnut boards and laminated them together (so I got 4 leg pieces with a square cross-section), and turned them into octagons using my jointer (you could just keep 'em square if you don't have one). I finally created a recess (I don't know the technical term) in the legs for the corner of the table to fit inside. I did this manually, using a hammer and chisel. There might be a better way, since I seemed to keep chipping off the top of the table-leg (the part that sticks out over surface of the table). It wasn't too bad, since I could just re-glue it, though.

Sand everything, and finish to your tastes. I used walnut oil, personally.

## Step 6: Conclusions

I think the optical illusion turned out very well, and the table's fairly sturdy- I can sit on it, although I wouldn't rough-house on it. Living in the desert, my main complaint with my table design is the sharp inside edges (where the maple edges and walnut legs meet the tabletop) tend to collect dust. I'd suggest either filling in this area with a custom sheet of glass, or sloping the border to avoid this nook.

I used a hand plane to do most of the smoothing of the table, and I hit a snag I made for myself; I shuffled all the squares in the course of cutting them, so all the grain ended up being randomized. I think it would probably look a lot nicer if you kept track of all the pieces relative positions (even better, make all the squares from one piece of walnut and one piece of maple, if possible, and keep them all in the same relative position). It would also make smoothing and finishing it easier.

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## 23 Discussions

To cut down on the dust collection, perhaps self leveling acrylic poured level with the outside edge of the coffee table.

Let us know next November if it survived the year without self-destructing due to the effects of wood movement.

UPDATE:

Not quite november yet, but it's still in great shape (my friends' beer spills notwithstanding).

Granted, I live in the desert in southern AZ where it never gets that humid, so I can probably get away with worse sins than others.

Hey, im building this in woodshop and i have everything layed out but the thing is i was wondering what the best way to clamp them onto the bottom table top while the glue is drying?
(pic if you want http://gyazo.com/c5e7996b4ab0e5e121521cc52947cbc1)

2 replies

That looks awesome!

I tried to glue them up just to each other at first, and couldn't get them to come out straight- so I glued them down to a piece of MDF, while I was gluing them to each other.

To clamp horizontally, I clamped a straight board across the work table, and used a second board to press the new row (I only glued up one row+spacer at a time) against it.

To clamp vertically, I just used another long, straight board across the row, which I clamped down against the worktable on each end.

This worked for me, but since I could only get two clamps on vertically, the better thing to do would probably be to use a slightly curved caul (e.g. http://www.leevalley.com/US/wood/page.aspx?p=67309&cat=1,43838) to apply pressure across the whole row.

Sorry for the super late reply but you helped me out a lot there and I just finished it. http://fav.me/d577itu
If you have a DA and want me to put that name in the description just send me a message.

Very cool! I think I want to use this pattern for my electronics workbench...

Very cool man! I think you just inspired me enough to finally try making a coffee table, haha. Did you find any other "decently easy" optical illusions that you may try after this one?

2 replies

Personally, I think this may be the best of the easy-to-make illusions. I've been looking at a good decent list of illusions at http://www.michaelbach.de/ot/ .

Other possibilities are the Munker illusion (3 colors look like 4)

http://www.michaelbach.de/ot/col_Munker/index.html
and
http://www.michaelbach.de/ot/lum_white/index.html

you might also be able to make the sine illusion

http://www.michaelbach.de/ot/sze_sineIllusion/index.html

finally, the "bulging checkerboard" illusion might be possible if you could use small circles instead of the little squares (make the checkerboard, drill a hole, use maple/walnut dowels to fill)

Here's a follow-up:

RE the "bulging checkerboard" pattern I found here: http://www.michaelbach.de/ot/geom_KitaokaBulge/index.html

you might be able to make the illusion as pictured with a square mortising machine, but I don't own one (no way you could do all that by hand). I made a mock-up of the pattern with circles rather than squares in GIMP, and the illusion remains, although it doesn't seem as impressive.

It also seems like it only works at certain scales; try zooming in and out on the image. when it's a thumbnail, it looks great; when it's full-screen, it looks lousy.

Very nice job HD :-)
Something to keep in mind when making chopping boards is that its important to only have end-grain showing. If you were to cut across the grain, you'd cut the wood fibres into short sections leading to small splinters coming free from the choppng board, not to mention blunting your knife. Check out the big chopping blocks at a butcher shop, although manufactured from smaller sized pieces of timber stuck together, they look like a huge square tree stump.

Chopping boards are relatively easy to make in the same fasion a your coffee table (which looks great btw) where you start with square timber and simply cut slices off it at whatever thickness you want your board / table. If I was going to make this coffee table, and I think I will cos its a great effect, thats probably how I'll go about it.

I loved your concernes about sharp knives, optical illusions and fingers! lol.

I am probably never going to build this but it looks great. Well done.

I was wondering if this method would be easier. In my head it makes sense but I dunno about to everyone else.
What if:
You rip the 3 maple boards and 3 walnut boards to width.
Then cut 5 strips of ash.
Glue the wood going maple, ash, walnut, ash, maple, ash, walnut, ash, maple, ash, walnut.
Cut the glued boards into long strips on the radial arm saw.
put the freshly cut wood on a piece of mdf and stagger them.
Then put strips of ash between each piece of wood.

Would that work or am I going crazy.

Yes, that should work. You'd probably have more luck with it if you had your long dimension running in the opposite direction as mine (my rows are super long). I'm not sure if that would make the illusion better or worse. Get a picture, crop it both ways, and compare!

The table is really cool, but I'm definitely gonna build my own cross-cutting sled! A rather simple solution for getting ungainly pieces cut.

Did you get a steel bar from and particular source? Presumably you just need something that fits snugly in the groves on your table saw.

2 replies

Shop-made tools are enormously useful, and can be deviously clever; I don't presume to be an expert in any way. If you'd like some details on how to make them, I'd recommend Mathias Wandel's writeup, from whom I admit to stealing the idea: http://woodgears.ca/delta_saw/sled.html

There are plenty of online retailers who sell steel stock; you probably want cold-rolled steel (I used stainless, but mild steel is probably also OK). I got mine from smallparts.com through amazon, if I recall correctly. onlinemetals.com is also a good source.

I agree -- The table is truly impressive, and you should put up an 'ible for the sled as well! Nice work.

This looks really cool. One question. Are the intermediate strips necessary?
Is it a structural thing or is it part of the optical illusion, or just an aesthetic preference? Thanks!