Making a jigsaw puzzle that has interlocking pieces is too ambitious for this book, but other types of jigsaw are possible. This project shows you how to build one that looks simple but is actually more difficult to assemble than the traditional type. And it’s a great way to become familiar with a wonderfully versatile material: plywood.

Where Plywood Comes From

When layers of wood are combined, we say that they are laminated. The concept of lamination stretches back even to the Egyptians, but plywood as we know it today is about 100 years old. It is manufactured now as it was then, by peeling layers of wood from a rotating log. Multiple layers are then glued together to create sheets.

Plywood is one of many wooden composites, meaning materials that are composed of small pieces or fragments, usually glued together. For additional details, see the Composites Fact Sheet on page 78.

The Strength of Plies

To see why plywood is so useful, I’d like you to do a little test. Start with a piece of scrap two-by-four, and cut a piece about ¾" long from the end of it. (The exact amount is not important.) Turn it so that the grain is facing upward, and clamp it to your work area as shown in Figure 6-1.

Saw a slice from this piece, across the grain, about ¹/₈" thick, as shown in Figure 6-2. Because this is a small slice, be especially careful about the saw jumping out. Keep your free hand away from the cut.

Take the slice between your fingers, as shown in Figure 6-3, and apply some bending pressure. You’ll find that the wood easily snaps in your fingers, as in Figure 6-4.

Now take one of the broken pieces and try to snap it in the other direction, along a line across the grain. You’ll have to use much more force, and you may have trouble breaking it at all.

The weakness of wood when it is stressed parallel with the grain can be a problem when structural strength is an issue. Furniture, for instance, has to be designed with this in mind. In addition, joining boards to make a large flat area is a time-consuming chore.

Plywood eliminates both of these problems. It is usually sold in sheets 48" x 96" (sometimes larger), and its layers, or plies, are glued at right angles to each other. Over any fixed distance, plywood should be equally strong in both directions.

Plywood is also relatively stable, meaning that it doesn’t tend to warp like a board or a beam. It comes in many different grades and thicknesses.

Figure 6-5 shows five samples. From top to bottom, they measure ¹/₈", ⁷/₃₂", ¼", ⁵/₁₆", and ³/₈" in thickness. The three pale-colored pieces are high-quality material from a crafts store. The piece second from the top came from a big-box hardware store and was their best-quality material in that thickness. The piece at the bottom, measuring ³/₈" thick, is the cheapest of the bunch, with only three plies and a rough surface of soft wood.

In Figure 6-6 you see a piece of high-quality ¾" plywood with nine plies and a birch surface. Again, this came from a crafts store. The type of ¾" plywood used in construction work usually has a rough finish and cannot be used for work on a small scale where the quality and detail of the finish are important.

I chose the ⁷/₃₂" plywood for the geometrical jigsaw. If you try to work with material that is thinner than this, you’ll have problems with it splintering. If you opt for thicker material, you’ll do more work sawing it. I think plywood that is no more than ¼" thick with a hardwood surface is an appropriate choice.

The Pattern

My plan for the jigsaw is shown in Figure 6-7. It looks simple, but you’ll find it is cunningly designed so that assembling the pieces is a challenge. Some of them have equal edge lengths, allowing them to fit together in many different ways, while others have edges that are not quite equal, to create confusion. I have also included a lot of 90-degree angles, so that it’s difficult to tell which pieces go in the corners.

I can think of three ways to transfer this pattern onto paper, so that you can then apply it to a sheet of wood. The simplest option is to photocopy the page from the printed version of this book, or copy-paste the image if you are viewing it on a computer screen. You can enlarge the image when you print or copy it, but it should not exceed 6" in the longest dimension, because you’ll have trouble making a longer cut with your tenon saw—as you will soon see.

Another option is to draw the pattern yourself, on graph paper. Stationery stores sell graph paper, or there are many web sites which allow you to download it free, after which you can print it.

A third option is to reproduce the pattern on a computer using vector-graphics software. I’m going to discuss that in detail, because this kind software is useful if you want to create designs of your own. And the application that I am recommending is free.

Vector-Graphics Software

If you are using photo-editing software, and you enlarge the image, the pixels get bigger—unless you resample the image, in which case you lose detail. This kind of software is not appropriate for accurate line drawings.

In vector-graphics software, the image is saved as a set of numbers defining lines and curves. A rectangle of a specified size will be reproduced at exactly that size, because the numbers store that information. If you double the size, you won’t lose detail, because the software simply doubles all the numbers that describe the shape.

Many vector-graphics programs exist, but the one that I suggest is OpenOffice Draw, because it is freeware for Windows, Mac, and Linux.

Go to www.openoffice.org and click the Download tab. Be careful that you don’t visit a site that has a name similar to openoffice; there have been some spoof sites that add unwanted toolbars or search bars to your download.

You will have to download the whole OpenOffice suite of applications, but after that, if you wish, you can install just Draw.

When you complete the download, start the installer and answer the usual questions until you reach the option to do a typical install or a custom install. Choose custom.

Now you can select the Draw component, and you can deselect everything else—unless, of course, you want the other applications. Writer, for example, emulates Microsoft Word, while Calc emulates Microsoft Excel. These applications can read Microsoft files, and can save in Microsoft formats.

Using OpenOffice Draw

When you launch OpenOffice, you’ll be able to select the Drawing feature, and it will show you a blank document. Here are the basic functions that you need to know.

Begin by selecting View>Grid from the menu bar, and make sure that Display Grid and Snap to Grid are both selected (click the little icon beside the option for each one, to toggle it on and off).

You should now see a grid of dots on the screen. They are pale gray and not easily visible, but we can fix that in a moment.

Select Tools>Options from the menu bar, and in the dialog box that opens, double-click OpenOffice at the top of the list, then Appearance in the submenu that appears. Scroll down to Drawing/Presentation and you can change the grid color (although it won’t become visible yet).

Go back to the mini-menu on the left side of the dialog box, double-click General, and you can choose your units of measurement. (On some platforms, this option is under the OpenOffice Draw menu.) I’m assuming you will want inches, but you can select millimeters if you wish. Now double-click Grid in the submenu, and under Resolution, you can choose the horizontal and vertical spacing of the bold dots in the grid. You can also specify the number of subdivisions. The default may be 5 or 10 (again, it depends which version and which platform you are using), but either way, I suggest 16, to make your drawing compatible with your stainless-steel ruler. Click OK, and the page on your screen should change in accordance with your settings.

Now you can use the line tool, the rectangle tool, or the ellipse tool to draw shapes on the screen. These tools are located at the bottom-left corner. Click on any tool to activate it.

You create each shape by dragging the mouse. Hold down Shift to draw lines at preset angle increments, or to create a square instead of a rectangle, or a circle instead of an ellipse.

After you draw an object, it selects itself, with little handles that pop into view. Now you can change the line thickness, line color, and fill color using data-entry fields at the top-left of the screen. Also, if you right-click an object (option-click, on a Mac), you get a menu which allows you to modify the object in various ways. Select Position and Size, and you will find options to resize, move, or rotate the object by exact amounts.

The crucial thing to remember, when using this software, is that you must have one or more objects selected before you can do anything with them. The Arrow tool (at bottom left, on the screen) allows you to click on any object, or select multiple objects by stretching a marquee (dashed lines) around them.

The program defaults back to the Arrow tool after you create any new object.

Draw is not a very elegant program, and it lacks many of the features that you find in professional-level software such as Adobe Illustrator. We shouldn’t be too critical of it, though, because it will do as much as you need for the projects in this book, and it costs nothing at all.

Awl You Need

Assuming you have printed the pattern onto paper one way or another, your next step is to transfer it onto your plywood. You can’t just tape the paper to the wood and start sawing, because the saw will rip and mash the paper. You’ll have to use an awl.

Just prick through each corner of the pattern into the wood, as in Figure 6-8, then remove the paper and draw lines between the prick marks, as in Figure 6-9.

Cutting a Work Piece

Assuming that your plywood is substantially larger than the puzzle, you should cut roughly around the puzzle to obtain a work piece that will be easier to deal with. Leave a margin of about an inch.

This is a rough cut, so you don’t have to worry about its exact position or quality. In fact, you would have difficulty putting sacrificial wood under the plywood, because the saw would have to cut through it. See Figure 6-10.

The rib along the top of the tenon saw makes it less than ideal for this long saw cut, but it can do the job.

In Figure 6-11, you see what happens to the underside of plywood when you don’t bother to reduce splintering. In this case, it doesn’t matter, as this edge won’t be used in the puzzle pieces.

Start With Some Stain

Thinking ahead, I want the top surface of the jigsaw to look different from the bottom surface, because if someone doesn’t know which way up the pieces are supposed to be, the puzzle will become almost impossible to solve.

The easiest way to make the underside look different is by staining it. Wood stain is easy to apply and dries very fast, but there are some aspects you should bear in mind.

• ■ Stain will be difficult to remove from hands, clothing, and work surfaces. Wear disposable gloves, dress appropriately, and protect the area where you are working.
• ■ Shake the can vigorously before opening it, and use a stirrer from time to time while the can is open, to make sure that sludge doesn’t accumulate at the bottom of the can.
• ■ Some types of stain are available in oil-based and water-based versions. I prefer the oil-based, but it must be used with good ventilation. Also, it is a fire hazard; you should not accumulate rags or paper towels with oil-based stain on them inside your house.
• ■ The color of the stain will be affected by the color of the wood that you use it on.
• ■ Check the label on the can carefully for additional cautions.

In Figure 6-12 you see how a paper towel can rub stain over the wood. Stain penetrates into the grain, and the longer you leave it, the darker it will get. After allowing it to soak in, you should remove any surplus from the surface by rubbing it with a clean piece of towel. Ten minutes later, more or less, you may be able to handle the wood without getting stain on your fingers.

The Cut Sequence

Now you’re ready to cut the actual pieces of the jigsaw. Does it matter which pieces you cut first? Absolutely! In Figure 6-13, I have lettered the cuts in alphabetical sequence. The rough edges indicate the rough cuts that you made to extract this piece from your larger plywood sheet.

The reason that the sequence is important is that each cut must go all the way from edge to edge of the piece you are cutting. Where you have a T-shaped intersection of cuts, the sacrificial piece that you are going to put underneath the plywood makes it virtually impossible to cut the vertical stroke of a T first. You have to begin with the stroke from edge to edge. Then you can do the vertical stroke, from edge to edge of the smaller piece. Figure 6-14 illustrates this.

Accurate Cutting

Accuracy is important in this project, because the pieces of the jigsaw have to fit together. Therefore, you will need a guide piece on top of the plywood, as well as a sacrificial piece below it. (I described these concepts back in Chapter 3. See page 27.)

Figure 6-15 shows the setup, and Figure 6-16 shows the first accurate cut in progress, along the edge of the jigsaw rectangle. Note that in this project you must cut on the lines, not beside the lines. This is because many of the cuts pass between the puzzle pieces, and you want to remove an equal amount of wood from each piece.

The saw has to tilt at a slight angle, because if you try to use it horizontally, it will tend to skate around instead of digging into the wood. The angle of the saw inevitably means that it will cut a groove in the sacrificial piece. That’s what the sacrificial piece is for, but it does mean a bit of extra work for you.

In Figure 6-17, the job has progressed to the cut marked E in Figure 6-13. In Figure 6-18, the last few cuts are being made, and are short enough to allow your guide piece and sacrificial piece to be turned around.

Finishing

Figure 6-19 shows the finished puzzle pieces. But wouldn’t it be better if you enclosed them in a frame, as you did with the sliding block puzzle in Chapter 1? Since you already learned how to make a mitered frame, this shouldn’t take long. The frame I built is in Figure 6-20. I added a back to it, using the remainder of the plywood.

If you ask someone to fit the pieces into the frame, I guarantee they’ll have a hard time—unless they realize that they can match the grain on the pieces, like the picture on a conventional jigsaw. Maybe you should prevent this?

The obvious way would be to cover up the grain with paint. On the other hand, maybe you would prefer to leave the grain visible, to provide a clue for solving the puzzle—in which case, you could polyurethane the pieces. I left my version unfinished. You can choose how to finish yours.