Introduction: CNC Wooden Car Toy
This instructable is inspired by Jimivandebeek’s awesome instructable for creating a Ford Mustang: https://www.instructables.com/id/Wooden-Toy-Car-F... as well as a number of other similar builds on the web. I loved the way that using plywood for the project added an extra dimension by showcasing the layers of laminations in the plywood, and how building up the body using multiple slices of wood allows you to create details in the exterior and interior of the toy.
Rather than using a scroll saw to cut out the slices, I thought this would be the perfect opportunity to learn how to use the CNC router at our local makerspace. Since the challenge with this kind of build is to make sure each slice aligns correctly, I figured that digitally controlling the cuts would be the easiest way to achieve identical pieces.
For the vehicle, I decided to make a toy of the Honda Element my mother owned, it has a quirky, recognizable shape and there’s lots of interior spaces that are interesting.
- 12mm (1/2 in) cabinet grade plywood
- 3mm (1/8 in) cabinet grade plywood
- 12mm (1/2 in) solid wood (maple / ash etc) for wheels
- Walnut veneer
- Woodworking glue
- Adobe Illustrator
Step 1: The System
The basic approach is that the body is made up of nine slices put together. The three slices that make up a seat section are all identical as are the outer and trim pieces. The middle piece has both separates the front seats, but also provides an opportunity to modify the profile to create some details on the inside of toy.
For example at the front of the toy the trim piece includes a cutout that looks like the signal light and the profile of the outer pieces is modified to suggest the headlights. The other example shows that by modifying the profile of the center piece you can create the center console which runs down the middle. So that’s the approach, here’s how we did it.
Step 2: Creating the Profile Outlines
Find a good illustration of your car, and import it into a layer in Illustrator. It’s a good idea to scale the image to the final size at this stage to avoid having to scale parts later in the process.
For the thickness of plywood that we are using here, 9 layers will create a toy that is roughly 4 - 4/12 inches wide, so it’s important to scale the size of the profiles so it’s roughly proportional to the real thing. This meant that for the Mustang it came out to be about 13 inches long, and for the Element it’s around 11 inches long.
Create the exterior profile first (black). We will use the first profile as a basis for subsequent profiles to make sure that they all match exactly.
Duplicate the layer with the exterior profile and lock the original layer so it doesn’t accidentally get modified. To make it easier to distinguish the layers change the color of the stroke (shown in red). Delete the paths around the windows and the tops. Delete the wheel arches and add some material around the axels. Add a small circle indicating the center of the wheel, it doesn’t matter the sizes it’s just there to mark where we will eventually drill the holes for the axels. Create a floor for the slice and a profile for the passenger footwell. I also modified the profile at the front to recess the front grill as detailed above.
Add a couple of seats and make sure the path is closed and continuous.
Add a profile for the roof section as well. Note you can generate the roof profile on a separate layer if you prefer to gang just the roof pieces for production.
Duplicate this layer and modify it to create the profile for the middle piece (shown in blue). For this piece I eliminated the front seat to create the gap between the two seats up front. Since the rear seat is basically a bench, I left that part of the profile in. In the front there is a console that houses the controls as well as a raised section between the seats, so the profile is modified to create these features.
The last profile is the optional trim piece on the exterior (shown in purple). There are cutouts at the front and rear which define the front and rear light lenses and there’s a cutout for the gas cap as well.
Then I made a quick profile for the tires (shown in green) to make sure the scale is appropriate. Looking at all the profiles together, you can start to get a sense of how everything will fit together.
Step 3: Save the Outlines
Save each path or layer as individual SVG files. For best results I copied/pasted each path into a new document and saved as an uncompressed .svg file.
Step 4: Create the 3D Parts - Importing the Profiles
I used Fusion360 to create the parts and the machine paths, and it’s a fairly straightforward process. There are a ton of great resources out there about how to use Fusion360 and I highly recommend it as an awesome (and free) maker resource that is worth spending some time learning. The following steps assume a basic understanding of Fusion360.
Note the process is the same for all the slices.
Create a new file and create a new sketch on the XY plane. From the insert menu select Insert SVG and select the file and place it in the drawing and click Finish Sketch.
Step 5: Create the 3D Parts - Extrude the Profile
Using the extrude tool extrude to the thickness of the material you will be making the slices from, in this case 12mm. Now you have the part created in 3D. Save the file as it's own slice.
Step 6: Create the Machine Paths - Setup
To create the machine paths, still in Fusion360, switch the workspace from Design to Manufacture. Then click the Setup button to create a new setup. You should see a bounding box appear, representing the minimum amount of stock the part takes up.
In the Setup options, set the operation type to Milling, and specify a co-ordinate system. This is key to making sure the tool head is oriented in the correct way. I’ve found the easiest way to do it is to choose the “Select X & Y axes” option and the select an edge on the model that represents the direction of the X axis, and then one that is in the Y axis. Finally select a Stock Box Point to define the origin. Typically I use the center point on the top surface of the model.
In the stock setup tab you can change a bunch of other parameters including different offsets to calculate the size of the material you need, but I tend to leave it set to the default settings.
Step 7: Create the Machine Paths - Cutting Tool Selection
Now that the the piece is oriented correctly, we need to define which tool to use. Note that Fusion360 comes with a large library of tools and holders pre-defined which you could search through to find one that matches your bit, but it’s very easy to add one to the library that matches the specs of the bit your using.
Click on Tool Library under the Manage icon to bring up the tool library. Click on Local/Library in the panel on the left to show any tools that are currently available in your local library. To add a tool click the New Tool icon in the toolbar:
Step 8: Create the Machine Paths - Defining the Paths
Once there is a tool saved in the library you can start defining the paths. There are two basic types of cuts used in this project - 2D Contour and 2D Pocket cuts. Use Pocket cuts to cut out holes in the material, and the Contour cut to cutout the exterior shapes. Note that the order that the the paths appear in the setup will be the order that they will be cut, so its best to cut out the pockets first and then the contour.
To define the first pocket, select 2D Pocket under the 2D toolbar.
In the options panel Tool tab click Select and choose the tool that you defined earlier. Click the Geometry tab Select the path at the bottom surface of the model to define the pocket.
Click the Clearances tab to set the various clearances for things like retraction etc. The screenshot above shows the settings that I’ve found work for me. Once you have set the depths click OK and you should see a visualization of the bit as well as the path that it will take.
Step 9: Create the Machine Paths - Preview & Export the Paths
You can also see an animation of the cut by clicking the Simulate button in the Actions toolbar, and click the Play button that appears at the bottom of the screen. This is not only fun to see but it will show where there are any potential collisions etc based on the current settings.
Continue creating any other pocket and contour paths needed to cut out the part. When you are done, click on the setup in the browser list and click the Simulate button to see how all the paths will be cut. If there are no collision warnings and everything looks good you are ready to create your .ns code for the CNC machine.
Click the Post Process button in the Actions section of the toolbar, and in the options panel select the correct post processor format for your CNC machine (the one I was using used generic Grbl format). Click OK to create the NC file, and save it to your computer.
Step 10: Cut Out the Parts
From this point, it's simply a matter of uploading the file to the CNC system, securing the stock to the base plate of the machine using double sided tape, zeroing the machine using the top of the stock as the zero reference, and running the code.
Unfortunately, I don’t have any photos or videos of the actual machining process, but it was very interesting and went well. A couple of things that I did learn:
You will likely only get one clean edge and that’s influenced by the type of cutting bit you have. An up cut bit will leave a clean edge at the bottom of the piece while a down cutting bit will leave a clean edge at the top of the piece. To minimize the rough edges at the bottom I also adjusted the bottom height parameter to 0.5mm below the bottom surface of the piece, since there was a sacrificial surface on top of the CNC bed. This helped but the other edge still requires a bit of finishing as you will see.
If I was to do it again, I would create two sets of NC codes where the second set is a mirror image of the first, allowing you to get nice finished edges on all the exposed sides.
Tape your pieces securely, and make sure that the pieces that are not waste are secured evenly. A couple of times I didn’t take this into account and there ended up not being any tape on one end of a part which would start to vibrate as it was getting close to being cut away which resulted in some slightly uneven edges.
Step 11: Sanding and Assembly Prep
As mentioned above, the parts come out nice and consistent, but they do require some cleanup needed. Here’s all the parts laid out after cutting, and you can see some of the rough edges.
Just like most woodworking projects, it’s all about sanding, sanding and more sanding. Start with 200 grit sandpaper to get rid of the tearout and clean up the edges. Using 200 and 400 grit go over the edges of the plywood until they are smooth. It’s much easier to do it at this stage rather than after the pieces are glued together.
Eventually, you get to the point where you are ready to assemble!
Step 12: Sub-assemblies
Gluing the pieces together in a staged approach works best and also allow you to do some finishing on the interior surfaces prior to final assembly. I started with the pieces for the roof. When gluing the pieces together, glue a piece at a time. On my first attempt, I had clamped all the pieces together at once and by the time it dried some of the pieces had shifted - it was only by a mm or two but it was enough to make it stand out visually and a real pain to sand. So what I did instead is for each slice, place a thin film of glue on one side and add it to the stack. Move it back and forth a little to help the glue set. The easiest way I found to match the contours is by touch - it’s much easier to tell when they are aligned perfectly. Hold it in place for a minute then add the next slice. Once you have the pieces together and aligned clamp to finish drying.
Glue the three slabs that make up the seats together first. Once it’s dried you can sand all the edges flush and get them ready for finishing. Once they are finished, glue the two seat sections to the center piece and clamp until dry
Step 13: Create the Holes for the Axels
Once the center block is completed, create the holes for the axels using a drill press and a 1/4” bit. It’s much easier doing this when all the layers are together vs trying to line up holes from the individual pieces and you’ll get a smoother hole for the axels. I used the depressions made in the profile as the guide to center the bit.
I used 3/16" dowels for the axles, so using the drill press I drilled a 3/16" hole in the middle of the wheels. If I were to do it again I would only mark the centre of the wheel when cutting it out rather than drilling the hole all the way through (or at least make the hole the correct diameter)
To finish the interior of the toy, I used a simple beeswax and mineral oil mixture (“wood butter”), wiping on a couple of coats and buffing with a cloth in between. Finish the inside surfaces of the outer slices and the roof then you are ready to assemble them together.
Step 14: Veneering Sections
I decided to cover the trim pieces with walnut veneer to create a color contrast on the side of the car. Cut out a piece of veneer big enough to fit over the pieces and glue them to the veneer, making sure that you flip one of the pieces so they are veneers on opposite sides. Because the veneer was curled quite a lot, I sandwiched the glue ups between two pieces of plywood and clamped them together to dry flat. Trim the veneer around the part with a sharp X-Acto knife, and use the blade to carefully trim the veneer flush to the part, and then smooth with the 220 and 400 grit sandpaper.
Working with veneer can be tricky especially when there are some small details, and some of the veneer did split off and needed to be repaired. I cut away a larger piece to Gove me both a straight edge as well as a reasonable amount of surface area, cut out a piece from a part of the veneer that matched it, and glued it in place. Trimming it as described above and it looked good as new.
Once the veneer is dry, glue the trim pieces to the outer slices of the car.
Step 15: Wheels and Tires
The wheels were cut out of a solid piece of stock, although there’s no reason that it couldn’t be made of the plywood as well. Once I had the wheel holes sized and mounted, I rounded over the edges with some sandpaper and decided to paint the tires black.
Masking off the face of the wheel with painters tape, I used a sharp knife to trim the tape on the inside corder of the recess, and put some tape around the axel right behind the wheel.
For the paint I just used some artists acrylic that I had laying around, but here’s a top tip: if you want your paint to look deep black, mix in some other color (blue / green / purple) as well. Pure black paint looks great when it’s wet, but can sometimes dry to a color that’s more like a really dark grey. So I mixed in a little purple and it came out great!
Once the paint is dry, peel off the painters tape and finish the tire with a bit of the wood butter and you are good to go.
Step 16: Made-by Sticker
I was making these cars for my nephew and niece, and was thinking about them as more of an heirloom piece so I wanted to make a sticker or decal on the car that was reminiscent of the manufacturer’s decals on some of the old tin toys I’ve collected.
I designed a label in Illustrator and printed it out at various sizes so I could see what was the right scale for the toy. Once I decided on a size and location, I used painters tape to mask out an area slightly larger than the size of the label. Using some Mod Podge® I painted it over the masked area and then centred the label on it and smoothed it out so there were no air bubbles underneath. After that layer dried, I came back and covered the entire are and label with 4 more coats letting it dry between coats. When I removed the tape, it looked like a decal with a clear edge.
Step 17: Finishing and Final Assembly
After the label was done, it was time to glue the outer slices, and to add the finish to the exterior of the car. Using the same wood butter as before, finish and buff the exterior of the car including the wheel well, and it’s time to assemble the wheels and axels.
When I cut the piece of dowel to hold the wheels, I made sure to cut it longer than the width of the car so I could later trim it to size. With the axel attached to one of the wheels, apply a little candle wax to the axel to lubricate it (I literally found a stick candle we had and rubbed it along the axel) and insert it into the car. Using the side of the car as a guide, cut off the excess axel dowel with a flush cutting saw. Ease the edge of the axel with some sanding, and then press the other wheel onto the axel, and rub a little wood butter onto the cut end of the axel. Repeat for the other axel and your toy is complete!
Step 18: Finished Toy
Step 19: SVG Files
If you are interested in giving this model a go, I've attached all of the profile drawings here. That are scaled and should be good to go. I've also included some mirror images of the profiles that are exposed on two sides so you can always have a profile with a clean top edge facing outwards. Have fun!
Runner Up in the
CNC Contest 2020