With a laser cutter and chipboard, we can make wood composite lasts to build custom shoes on.
Before we start building, you will need:
1. A CAD model of your last or other object you'd like to make. Designing a custom last is a bit out of the scope of this Instructable, but if you're comfortable with 3D modeling, you can start by using Autodesk's 123D Catch to scan your foot, and build a last model based on that.
2. Chipboard or other wood fiber composite (thinner materials will give you better part resolution).
3. Wood glue
4. [Optional] Small paint roller
5. [Optional] Paper or cardboard to cover your workspace.
6. [Optional] A fixture to register the parts of your last.
Step 1: Preparing a 3D Model for Cutting
Export your 3D model from your modeling program as a STL or OBJ file. Import it into Autodesk's 123D Make to be sliced. Since it's important for the last to be the correct dimensions, I set my initial slice width to the chipboard thickness, cut some parts and build a sample, measure the sample's width across slices and divide by the number of slices, and then re-enter that value in 123D Make. This ensures that my slice width includes the average thickness of the chipboard plus wood glue which I use to build the last. Here, I used 14-ply chipboard, which is nominally 0.05", but comes out to about 0.0523" after gluing. Export your cutting paths from 123D Make in whichever file format is convenient for you. I use DXF, do some post-processing in AutoCAD, and then generate cut files for my lasers from there, since AutoCAD can treat them as plotters.
While 123DMake has several nice alignment options like pinholes, etc. I prefer to create CAD for a separate part, called the carrier, which mates with the bottom surface of the last. This part also gets sliced - making sure to do so in the same direction as the last model so that the pieces are numbered in the same direction. By assembling the pieces in the opposite order, the same CAD file can produce either a right or a left foot last. Therefore, I cut two sets of the last part (for right and left), and one set of the carrier parts (which are used for both lasts).
Step 2: Interim - Decide How You Will Register Your Parts As You Stack Them
Because I use carrier parts, I need a fixture to register them in. I built this two-sided fixture to place the parts in.
Step 3: Sort Your Laser Cut Parts
After you've laser-cut your parts, sort them into the proper numeric order, and split the stacks in half. We'll build out from the middle so that the smallest parts are always on top.
Step 4: Begin Gluing Your Parts
Starting with one stack of parts, place the largest carrier part in the fixture, biasing its rectilinear edges against the two carrier walls.
Place the matching last part so that it nests with the carrier part.
Place the next carrier part on top of these parts in the fixture, again biasing its rectilinear edges against the two carrier walls.
Step 5: Adding Glue
Select the part that matches the previous carrier piece you placed in the fixture. Check which side will be facing down in the fixture (based on which way it nests in the carrier part).
Turn this surface up and apply glue to it. Using a paint roller or your finger, evenly spread the glue over the surface.
My dad always says, "A good glue bond should sweat but not drool..." so go light on the glue. What he means is if small beads of glue appear on the edge of your glue bond, that's good, but huge drips shouldn't pour out the sides.
Step 6: Align Part and Press
Taking your glue-prepared part, align it to its carrier in the fixture, and press it firmly down in place.
Step 7: Repeat....
Repeat the previous three steps until half of your last is glued up.
Place a spare piece of wood on top of your stack of parts in the fixture (it helps distribute the clamp's pressure), and use a bar clamp to clamp the stack for at least 15 minutes.
Step 8: Excavate Your Work So Far
Remove the stack of parts from the fixture and remove the half last from the carrier pieces.
Step 9: Build the Other Half of Your Last
Now turn to the other stack of parts - the other half of your last. Place the carrier for the largest part in the fixture, but make sure that it's facing the opposite way from the parts in the first half. For example, if the numbers etched into the parts to identify them (123D Make automatically adds these) were visible while assembling the first half, they should not be visible now.
Apply glue to the last part that matches the carrier part in the fixture, and repeat the assembly steps from the first half last.
Step 10: Excavate Your Second Half Last
Excavate your second half last, and set your carrier parts aside if you plan to build a second last.
Step 11: Glue the Two Halves Together
Apply glue to the largest face of one half last, align it by eye to the other half last, and clamp together. It's especially important that this glue surface not have too much glue, otherwise it will slide around as the clamp is tightened. Leave for at least 15 minutes.
Step 12: [Optional] Build Your Other Last
If you cut two sets of last parts, you can build a mate for your first shoe last by reusing the carrier pieces and following the original steps - as long as you are careful to assembly your parts in the opposite order. For example, if the numbers are visible on the instep of your first last, they should not be visible on the instep of your second last.
Step 13: [Optional] Build a Pair of Shoes on Your Lasts
Once you've built your lasts, you can wrap tape around one of them, sketch where you want seams to go, and then use an Exacto knife to cut along the seam lines to make flat patterns (the patterns can be flipped over to cut parts for the other shoe). Cut these patterns out of suede or fabric and sew them together to make the upper for a pair of custom shoes!
For extra points, you can build patterns from your original 3D CAD model. The shoes shown above were built on lasts assembled according to this Instructable with CAD models that were adjusted to a set of customer dimensions (image credit: SFT Climbing).