- Published: Friday, 22 March 2019
- Written by Jon Chandler
- Hits: 619
When you've designed a great new gadget, you may want to put it into an enclosure so it can easily be used and to protect it. There are many options to accomplish this, ranging from Altoid tins to commercial enclosures to custom designed and built enclosures. Let's briefly look at some options.
A quick Google search shows hundreds of projects built into Altoid tins. This can work well for small projects and people have accomplished some amazing feats cramming a lot of stuff into a small package. But sometimes you want something more professional looking.
Off the shelf enclosures come in not just rectangular boxes but in all kinds of shapes and sizes. The pictures show some pretty standard types for Pactec and the rather unusual Blob series from OKW. For a one-off, you may want to do the machining yourself, but the suppliers will be happy to do this for you if it's something you're going to make in bulk.
One important piece of advice - if you plan on using an off-the-shelf enclosure and put a circuit board of your design in it, decide on an enclosure before laying out the circuit board. This will ensure that your board will actually fit an available enclosure and mounting holes will be in the right locations to use mounting bosses and so forth. This diagram shows a circuit board to fit in a Hammond Engineering enclosure. I like to include the outline of the enclosure to aid in positioning connectors and switches.
As an alternative to off-the-shelf enclosures, laser-cut acrylic enclosures using slots and tabs may be machined to any size you like. There's a good tutorial here on laying out this type of enclosure. Many low-cost electronics modules from China feature enclosures of this type and they have elevated it to a high art form, incorporating laser-cut pieces to operate slide and pushbutton switches and other features. The picture shows a cheap oscilloscope module I purchased recently. If you have ever tried to put one of these puzzles together, you know how challenging it can be to get all the pieces in place while getting it screwed together!
Creating a Stylish Enclosure
*This article almost never happened. I got most of the artwork together on Sunday, including a picture of the Hexalithius blocks from the Elecrow website. Monday morning I was working on the text and went back to Elecrow to get a link to the blocks. Overnight, the price had been slashed by 90%, and Elecrow only had one block left! It appeared that all my efforts in designing the following enclosure were for nothing. Fortunately, after I finally reached someone at Elecrow, they were helpful and located an alternative block on Ali Express.
I was faced with the challenge of creating a desktop enclosure for my Wake Turbulence Timers for the FAA. These timers are designed to mount in a cutout in the console in control towers but a desktop unit was requested for use in training. I needed to accommodate the existing panel size as they already had the timers and nothing available off-the-shelf would achieve a professional result. I used
Elecrow's Hexalithus 10mm × 10mm × 10mm blocks and laser-cut acrylic to create a stylish custom enclosure. Similar blocks of 10mm × 10mm × 6mm are available from Ali Express which will work exactly the same with some slight hole repositioning (I think). This picture shows what I think the difference to be although I don't have any of the Ali Express blocks to be certain. The Elecrow blocks have a tapped hole in the center of each face, so the face of the block is 5mm from the hole. I believe the Ali Express block also has tapped holes in the center of each face so on the "front" face, it's 5mm to each side. On the "side" faces, the holes will only be 3mm from the side faces in the short dimension. It does make the layout a little more confusing.
A Hexalithus block is a 10mm metal cube with a 3mm hole tapped through each face. Using 8 blocks, you can secure panels to create an enclosure. The sides must meet orthogonally (i.e., at 90°), but this doesn't pose a limitation on creating a stylish enclosure. Follow me as I design an enclosure for the Wake Turbulence Timer, and I'll explain the key points along the way.
The timer panel is 6.5" x 4", with the happy circumstance of the mounting holes being located 5mm from each corner, with is perfect for the Hexalithus blocks. the panel is shown below.
Let's start by positioning a Hexalithus block at each corner of the panel. These will be located behind the panel but they are shown on top for clarity. We're going to start by building a rectangular box around the enclosure. The top, bottom and sides will extend past the sides of the panel to be flush with the front although they could extend further if desired to protect connectors or switches.
The next picture shows the top, bottom and sides of the enclosure. I'm using 6mm acrylic for these parts to give the enclosure strength and some heft. I want to cover as many cut edges as possible, so the top extends over the sides, and the bottom is covered by the sides. You must know the thickness of the material you're going to use to ensure proper overlap at the joining surfaces. In this case, you might make the top a little wider than needed to provide a small reveal and ensure the sides are covered. A couple notes about acrylic. First, it's usually 3mm or 6mm thick even though it may be called 1/8" or 1/4", but check to be sure. Second, there is some variation in thickness depending on the manufacturing process.
The sides run long in this picture. I want to angle the box that encloses the timer by 20 degrees to provide a nice viewing and operating angle when the timer is on a desktop. This is where we get to be creative. The sides will provide feet to support the timer at 20 degrees. The feet must extend in back of the enclosure far enough to prevent tipping when the buttons are pressed. Feet extending out about equal to the back top edge of the enclosure should be sufficient.
One addition we could easily make to to extend the front edge of the top to provide some shielding from overhead lights for the LED displays. The sides will taper from the edge of the edge of the extended top to meet the edge of the bottom panel. Applying some curses to the rough shape of the side will make a pleasing shape. The side I used is shown below. I finished the bottom with distinct feet from and back so the enclosure will not rock on non-perfectly flat surfaces and added a slight recess to accommodate 1/4" 3M Bumpon non-skid feet. The timer itself is contained in an orthogonal box, but the sides of the enclosure give it some character.
The back panel is 3mm thick like the from panel and positioned so the panel is flush the the sides, top and bottom. There's a hole for a full-size USB B connector and no other connectors, so the panel doesn't need to be recessed to protect any connectors.
This enclosure may be used in control towers, so it's desirable that the surfaces are non-reflective. I used P-95 acrylic material which has a matte surface on one side rather than the typical shiny surface of acrylic. Because only one side is finished, parts have a good side and a bad side. Non-symmetric parts like the sides therefore have a left-hand and right-hand part.
I draw my parts in Visio. One feature of Visio makes this very easy. The top is 6.5" wide plus 2 x 6mm to overlap the sides. The dimension box in Visio is smart enough to understand the dimension [6.5" + 12mm] so I don't need to do all the conversions and make the calculations. Be sure the screw holes take the overlaps and recesses into account. For example, the holes on the sides must be 5mm below the top edge (since the top overlaps the sides) and 5mm + 3mm from the front and back edges to allow for the thickness of the front and back panels. The drawing below has 2 sets of the pieces from the 6mm material, with sides flipped to provide left and right hand versions. This version adds a small shelf in the back to support a rechargeable USB battery so the timer won't need to be plugged into AC power. There is an extra bottom piece to modify one of my existing prototypes.
Assembling The Enclosure
The screws used to assemble the enclosure are critical to success. Screws will enter the block from 3 sides. If the screws are too long, they are going to crash in the middle of the block. Considering the Ali Express version, screws on the 6mm x 10mm faces must not extend into the hole coming from the front face, It's 5mm from the block face to the center of the block. The holes are tapped for 3mm screws, so the edge of tapped hole is about 3mm from the face of the block. For 3mm material, a screw length of 5mm or 6mm may be used. For 6mm material, a length of 8mm is the option, as 9mm length screws are not commonly available. A variety of head types may be used. I generally like the low provide look of button head screws. Truss head is another low-profile option. McMaster-Carr has a large variety of screws available if your local hardware store is lacking.
I start the assembly of the enclosure by fitting blocks to the four corners of opposite sides with the screws loosely tightened. The photo shows the blocks attached to the enclosure sides.
Next, attach the enclosure top and bottom to the sides. Notice how the top overlaps the sides, and the bottom fits between the sides. The closeup shows the overlap details. From these pictures, it looks like the top and bottom aren't parallel but they are.
Next, the back is put is put into position. Note how it fits inside the sides. This minimizes the cut edges visible and adds rigidity to the enclosure. If the device has connectors requiring protection, this panel could be recessed to provide protection to them. At this point, the top and sides can be slightly moved around due to the clearance of the screw holes to close the joint between side and top as much as possible. The process can be repeated with the front panel to minimize any gaps. Tighten the screws on the sides, top and bottom to complete the assembly. The enclosure is free-standing at this point; the front and back may be installed when it's convenient. This is one of the key points of using this method to create an enclosure - any panel may be removed without causing the enclosure to collapse. Opposite sides may even be removed without problem.
The photo below shows the foot detail of the side, showing the small recess for the Bumpon feet. Note the matte finish of the side thanks to the P-95 acrylic unlike the typical shiny surface of acrylic. This is important to prevent glare in the control tower.
To prevent the Wake Turbulence Timer from siding around or tipping when the buttons are pressed, I added a mass under the bottom of enclosure - there's no room inside the enclosure because the standard timer panel was used. The could be done with a piece of steel bar stock cut to length but I used an easier method. Simpson Strongtie sells what they call tie plates. These are 20 gauge steel plates available in a variety of sizes for joining lumber together. USP sells a similar product they call a mending plate. These two products appear to be identical, except for the position of the holes - this illustration is the Strongtie part, the photos show the USP part with the columns of holes swapped. The TP-15 or MP-15 is the prefect size for this enclosure - 5" x 1-13/16".
I created a mass by stacking up 8 of these plates, and covering the stack with a piece of 1.5" diameter heat shrink tubing. If the ends overhang the plates by the total thickness of the stack, the ends will be covered when the tubing is shrunk. I cut the tubing a little shorter than ideal in this case.
The mass mounts under the bottom panel of the enclosure with four 3mm screws. It's barely visible when looking at the enclosure from the normal position and makes the enclosure rock-solid on the desktop.
Here's the beauty shot of the completed enclosure with a Wake Turbulence Timer mounted in it. It portrays a quality product in a custom-made enclosure.
It is possible to create something more that a rectangular box using these mounting cubes - the resulting enclosure can be very stylish and fit the need perfectly.
This method isn't the cheapest way to make an enclosure. The cost of blocks, acrylic, laser cutting and hardware add up to around $75. The result is a nice enclosure like no other that exactly fits my needs.
For information about the Wake Turbulence Timers, please visit www.WakeTurbulenceTimers.com.