HOW TO MAKE A CUSTOM PLASTIC ENCLOSURE REQUIRING A RASPBERRY PI USING THE TOOLLESS PROCESS
The purpose of the following is to explain the process Toolless uses to manufacture a custom plastic enclosure. To explain I will go through the process as if we were making an enclosure that will hold a Raspberry Pi 4–something a lot of our customers contact us about.
WHAT’S OUR PROCESS?
To begin, there are two important things to keep in mind as we go through the process. First, our process does not involve injection molding. All our enclosures start as flat pieces of plastic. Typically, a sheet measures 4’x6’ with a variety of thicknesses ranging from 2mm to half an inch. The ABS used in this case has a smooth side and a textured (horse-cell) side. We normally want the textured side on the outside of the enclosure because the smooth side is extremely susceptible to scratches. For this Pi enclosure, we used 3mm black ABS.
The second thing to remember is that we do not stock enclosures. If you order 50 enclosures, we make the 50. We do not have any that are waiting on a shelf for someone to order. Even customers who have been with us for 25 years do not have theirs on a shelf. You never know when a change or modification needs to occur and suddenly that enclosure is out of date. Every customer gets enclosures manufactured as they request more.
WHAT RASPBERRY PI MODEL IS IT BASED ON?
The Pi enclosure we are making here uses a design we call an EB200 (EB stands for Easy Box). We also refer to it as a “C” box because it will ultimately end up as two parts in C shapes that will snap together using a tongue-and-groove technique. Making a Raspberry Pi enclosure, whether for a Pi 3 or a Pi 4, is one of the least complex custom plastic enclosures that we manufacture. We do not require every operation or process for every enclosure that we make. However, I will walk you through each process — regardless of its completion for this enclosure — so that you can better understand the Toolless Way. The process includes seven steps: Design, milling or CNC (Computer Numerated Control), Saw, Printing, Bending, Assembly, and finally Shipping. I will briefly discuss each step and conclude with different options that are possible.
WHAT ARE THE DESIGN DETAILS AND CONSTRAINTS?
Once the Sales Department has worked out the financial details–the first step is CAD (Computer Assisted Drafting). A CAD Designer, who has been assigned to your project. They will contact you and work out the details of your custom plastic enclosure. While it is possible to buy an enclosure to house your Pi board, with Toolless Plastic Solutions your enclosure is custom-made to expose or conceal the components you choose. This allows for multiple options and a wide range of opportunities to ensure the enclosure has all the features you require.
In the example we use here, the customer wanted room for a fan and vents to improve airflow as well as access to all the components on the Raspberry Pi 4. The CAD designer’s goals are to provide you a functional enclosure, one you are pleased with aesthetically and can be easily manufactured repeatably. In other words, can we easily repeat the manufacturing process to produce quality enclosures in a time frame acceptable to the customer?
The CAD Designer will provide a 3D model or 2D drawings to finalize the design. Once the design has been approved by the customer the CAD Designer will use the model to program the CNC program and develop a Shop Traveler.
HOW DO WE MANUFACTURE THE CUSTOM PLASTIC ENCLOSURE?
The Shop Traveler is the manufacturing plan used by the shop to make the enclosure. It provides direction on the material to use, dimensional requirements, the CNC milling order, what bits to use, directions, and special requirements for the saw operator, printer, bend operator, assembly, and shipping. With the Shop Traveler printed, it goes to the CNC operator to begin Step 2.
The CNC operator selects a sheet of plastic based on the required color and thickness described and places it on one of our seven CNC machines. As much milling as possible happens on the smooth side of the plastic as possible. This helps to keep the textured side which is what a customer sees as crisp and clean as possible.
Let us say the first part that the Operators mills are the inside “C” or the bottom of the enclosure. The part has been programmed as a flat part which has the openings for the USBs and ethernet on one side and the opening for the SD card and two holes to see LEDs on that side of the board.
The inside dimension of this enclosure is 57mm wide, 83mm long and 47mm high. This will make the inside part, when flat, a rectangle measuring 183×59. The 183 is the inside height times two with an additional 1mm on each end for the feeders. It also includes 6 more mm’s (3mm each for two bend cuts). The 59 is the inside width plus 1mm feeders on each side. Very confusing on its own, but our CAD Designers, with the help of SolidWorks, are quite capable of creating the necessary programming needs for milling the correct parts.
First, The CNC Operators mills one part and evaluates the outcome. Then, a general observation is made to see if all the features on the Traveler match the milled part. At this time, a dimensional check is made of the length and width, hole diameter dimensions, and any depth of recesses as well as any other dimensions the CAD designer considers critical. If there is an error detected the CNC operator consults with the CAD Designer to resolve the issue. Once everything checks out the CNC operator will mill the required number of parts.
After milling of the inside “C”, the outside “C” (or the top of the box) starts the milling process. In this case, it will have cutouts for the USBC, Micro HDMIs, audio jack, and a slot that runs near the outside perimeter this will accept the feeder to hold the enclosure together. The outside C will also have the milling operation on the smooth side of the plastic. CNC has been programmed to make a frame that will accept the milled part and enable the operator to mill on the other side. This will make the recess for the HDMIs and the USBC. It also adds a couple of decorative grooves across the top. Upon completion of the milling operation, both parts are put in a bin with labels and move to the next operation.
The number of parts milled will always be more than the order requires. For instance, if you ordered 25 enclosures, the CNC operator will look at the number of operations which will follow the first milling and increase the number of parts. This is to compensate for tests and machine set up in the operations to follow, more on this to follow. In this example, we could expect the CNC operator to make 6 extra parts.
Step 3 is the saw which normally does two kinds of cuts: feeders and bend cuts. We have three large table saws with the blades mounted from below. To start, the saw operator will take a scrap piece of plastic that is the same thickness as the part and place it on the table. The operator refers to the dimensions on the traveler. Next, the saw operator will adjust the saw as required and cut the scrap. After making necessary adjustments he will cut his first part. This is where the extra parts are sometimes required. If the cut is not within tolerance, then we have one less part to use.
Normally the first saw blade used will be a 90-degree blade to make the “bend groove.” The width of the bending groove is normally the same as the thickness of the material. So, for this case, it would be 3mm.
The other blade normally used is a flat blade to cut the feeder. Once again, the saw operator will make several test cuts on scrap and then use the parts milled by CNC. The saw operator tests the fit of the two pieces and makes several dimensional checks to ensure the parts are within tolerance. Once saw has finished the parts they move to the next operation. The shop traveler indicates the order of operation. Typically, after the saw operation a part will go to printing if necessary or bending. However, occasionally a part will go to assembly or shipping after saw. It is dependent on the enclosure and its needs.
Step 4 is printing. We have three printers that we use to print on parts. Sometimes a customer wishes for their logo printed. Other times, the customers wants labels (on/off, HDMI, input, output, etc.) for the different cutouts and slots. We use UV solvent ink with our printers and can print multiple parts at a time depending on the size of the part. Upon completion, the printed parts move on to the next operation, which is typically bending.
This is where the parts will really begin to take the “C “shape of the custom plastic enclosure. We have several bending machines which operate on the same technique. First, the operator sets up the bending table to match the size of the part. Next, the tables will then heat the area along the bend cuts while adding pressure on the parts. Finally, once the pressure exceeds the plastics’ ability to remain flat it will bend the parts to a 90-degree angle. Each of the two parts for the Pi box will need two bend operations. The bending operator will also make dimensional checks after the parts take shape as well as a test fit. The two “C” parts will then move to the designated assembly area.
Assembly is an optional operation, which depends on the customer’s needs. Here is where we install any accessories needed in the enclosure. Each type of plastic has a special bonding procedure required to optimize the security of accessories. Accessories that we can add include standoffs, inserts, light pipes, screws, acrylic windows, tabs, and more. When a shop traveler first comes to assembly, the assembly lead will create a setup box. In other words, this is the complete enclosure with all operations and accessories. The CAD Designers review the setup box for initial approval and dimension checks. Upon approval of the setup box, the remaining parts go through assembly. Parts that require bonding or glue remain in the assembly area until they cure properly before moving on to shipping.
The Shipping section has two responsibilities. They are the final operation to ensure the custom plastic enclosure is a quality product. Shipping cleans and inspects for fit and form. They check the traveler to see if there are any specific instructions for testing or quality checks.
The final stage is packing the enclosures to prevent damage during transportation and finally addressed and shipped to the correct address using the best method.
The custom plastic enclosure used in this example secures the board in place by using internal slots and the inside of the enclosure to hold it in place. But what if you did not want access to the SD card? We would have to move the board away from the inside surface. In that case, we would use circular standoffs (sometimes called bosses or spacers). We use a soldering iron to melt brass threaded inserts into the standoff. There are circular recesses milled into the bottom for alignment and gluing.
The list of options is almost endless. There is color and thickness of the plastic as well as types of texture. You can also decide which components need to have exposure, reversing the “C”, adding flanges for mounting, or securing the enclosure together with tabs.
It all starts with the CAD Designer to discuss the way you want your enclosure to look.