This popup-book style paper mechanic involves pulling a tab and having a part of a scene move in a straight line in the same direction the tab is being pulled.
I used normal printer paper for this project, but the results will be more durable and will have smoother action if you use a heavier stock with a smooth surface. Quality, not thickness, is important when selecting an appropriate card stock. Construction paper, though thick, lacks the structural strength, and even the thinnest cardboard (think cereal box) seems to be thick enough that it just binds up.
Step 1: Sketch Out the Housing
There are two important measurements that must match up between the two pieces:
A) the height of the guide strip along which the item will travel
B) the length of the strip of paper along which the item will travel, plus a spacer between the end of the guide strip and the slot for the pull tab. Leave some space between the pull tab's slot and the edge of the paper in order for the pull tab to have somewhere to lay on the surface.
Sketch out the guide strip on the housing first. The strip should be fairly thick (A) in order to be rigid enough to keep the slider on-track, and the two sides need to be very straight and very parallel. When determining its length, Give it around an inch and a half of space on the side where you want the pull tab to be.
Just past the end of the guide strip, draw a line perpendicular to the strip. This strip should be slightly bigger than A in order to accomodate the full height of the tab, plus just a hair in order for it to slide without binding. The distance between the end of the guide strip and the slot can be as large as you want it to be, but you may be trading travel distance in order to do so, and that's absolutely fine.
You may have noticed that all of the cut lines that I've drawn have a slight curl at the end of them. This is to help prevent the housing from tearing as the slider hits each end of the guide strip, and the tab from tearing the corners of its slot. It both redirects the force of the blow a little bit, and also allows the slots to expand up away from the face of the paper, allowing multiple layers of paper to be pass through each other without tearing open. This is much more important when using thicker stock.
Step 2: Sketch Out the Slider
The height of the guide strip will be 'A', and should be slightly smaller than the pull tab. The pull tab should be slightly taller than the guide strip to help prevent it from buckling and pushing the guide strip up away from the plane of the paper when pushing the tab back into it's "home" position.
The length of the slider must be longer than B in order to have enough material to stick out past the vertical slot. The distance it extends past the slot will be the size of your pull-tab.
At the opposite end of slider than the pull tab, draw a flange above and below your slider, each with a height of 'A'. These flanges will stick through the slots on either side of the guide strip, and we will eventually glue these together creating a ring around the strip.
Note that the cuts for the flanges extend down to the 'A2' measurement of the slider, not to the height of the tab. This is where the transition between 'don't let the slider escape' transitions to 'the slider needs to be seen here'.
Step 3: Cut Out the Pieces
Cut along all the solid lines. You will need a hobby knife to cut the guide strip and slot for the tab on the housing. Don't cut in from the side to access them.
There is a third strip of paper in my sketch. This is an optional reinforcing piece that we will discuss later. Feel free to ignore it for now.
Step 4: Mesh the Slider and the Housing Together
Once you have the flanges through the housing, bend one flange so it completely overlaps the guide strip. If you bent one of the flanges when pulling the flanges up through the slots, use that same already-bent flange now.
Stick the pull tab up through its slot in the housing.
Arrange the two pieces so that the guide strip is snug up inside the bend of the bent flange.
Now bend the second flange over the first, using the slot of the guide strip to determine the exact location of the fold. It might be that your measurements were off when sketching, but if you adjust the fold location to match the slot, any error in measuring gets smoothed over.
Apply a sparse amount of glue between the two flanges and clamp them together (like weigh them down with a book). You must take special care that there is not so much glue that it will squeeze out and cause the flanges to become glued to the guide strip, or your project will be ruined. I've found that dropping one drop of white glue on a flange and spreading it around with a toothpick gives good coverage.
Step 5: Reinforce the Tab Slot (optional)
Remove the pull tab from its slot.
Cut a strip of paper the appropriate width. The strip of paper used to make this optional ring must not overlap either the guide strip or the pull tab slot. The length of the strip should be around three times the width of the tab (which is just slightly larger than our original A).
Fold the strip in a ring around the tab, similar to how the flanges got wrapped around the guide strip.
Once you have two folds, glue the strip to the BACK of the housing, between the tab slot and the guide strip.
Glue the two flaps together, closing the ring.
Once the glue has dried, slip the pull tab through the ring, and back through the tab slot so it is once again visible from the front of the housing.
Step 6: Close Up the Page
If you want a cover for your work, you can certainly add that as well. I intend to showcase additional mechanics moving forward, so you may want to hold off and make a book once you've gotten a couple more tricks up your sleeve!