This project describes how to build a very rugged and elegant looking hard case for an electronic eReader of the Kindle variety. It can easily be adapted for other eReader sizes.
Electronic gadgets are very useful. Damage can occur with rough handling and transport, especially in a duffle bag or backpack. Making a container with sturdy sides will protect the contents during most transport events.
Envisioning the finished product :
Two-dimensional sheets can be stacked into a three-dimensional object to create a box with interlocking halves. The best way to describe the finished product is to characterize it in terms of a sandwich. If you stack multiple slices of bread on top of each other, cutting rectangles in the middle slices, you end up with a solid top, a solid bottom, and a protected area inside the middle rectangles. Make the slices big enough, and an eReader will fit inside.
When finished, all of the layers of this "sandwich" (rectangles) will have 0.50-inch radius rounded corners. This produces a very attractive and durable container. An edge-rounding router bit with 0.0625-inch radius eliminates any sharp edges on layers with outside edges.
Step 1: Shape, Size, Structure
The thickness of the laser cut kerfs allows the top and bottom halves of the container to fit snugly, but not too tightly.
Actual measurements on the Kindle with a cover that includes the LED light : Dimensions: 5 3/8 x 7 13/16 inches (5.3750” x 7.8125”)
Rectangle size, inside dimensions: 6 x 8 inches
Rectangle size, outside dimensions: 8 x 10 inches
Rectangle side width: 1 inch on each side and 0.50 inches on center layer sides
Rectangle corner radius: 0.50 inches
Acrylic sheet thickness: 0.220 inches nominal, 0.198 actual
All holes are 0.23 inches in diameter
Note the layout here:
First Image: The Center and 3x Middle layers.
Second Image: Top, Bottom and 2x Middle layers.
The 5 middle layers are identical.
The 2 top and bottom layers are identical.
There is only 1 Center layer.
These eight layers assemble as follows:
1. Top Layers 1-4 are 0.792 inches thick - Top half of container
4. Center This layer has two interlocking rectangles each 0.50 inches wide
8. Bottom Layers 4-8 are 0.99 inches thick - Bottom half of container
Layers 1-8 are 1.584 inches thick - Total container thickness
Layers 2-7 are 1.188 inches thick - Total space for eReader
Recall that each part is 0.198 inches actual thickness.
The cutouts from each layer consist of enough material to use in another project.
Step 2: Tools and Materials
- Understanding of CAD layout techniques.
- Someone with operational knowledge of laser cutters.
- Familiarity with routers or trimmers and cutting bits.
- As always, YOU are responsible for your own safety.
The eReader hard case project uses:
- CAD software (Corel Draw X4),
- A laser cutter,
- A router or trimmer with a round over router bit with 0.0625-inch radius (1/16”), and
- a flat head screwdriver.
2 sheets of Acrylic plastic (18 x 24 inches and 0.220 inches thick) $16 ea = $32
8 fasteners (post screws) ~$2 ea = $16 (if all holes are used you will need 16 fasteners , they were more expensive than I expected and so I only got 8)
1 hook and loop band (2 inches wide and 36 inches long) $8 for 2 straps (though you only use 1) = $8
Total approximate material cost: $56
Note that this is for materials only, and doesn't include the cost of laser time.
Step 3: Download CAD Files
- Add more layers if the material you buy is thinner
- Optimize the part layout for the size of material and laser cutter table size
Important Note :
The attached CAD files are in Corel Draw X4 format (.cdr); Also available are the .dxf files. If you own some other CAD program, importing a DXF file might not work properly since curves can sometimes cut 15 or 20 times. This condition is an error and a serious timewaster on the laser cutter. Consider making a new CAD drawing with the CAD program that you have on hand. In any case, make sure that the laser cutter will accept the format and output that you plan to use.
CAD Drawing notes :
Any CAD drawing simplified into a sequence that eliminates as much time-consuming effort as possible is worth the preparatory effort. This drawing began with the most complex part: the center layer. Once designed, duplication into different positions streamlined the process. Unneeded feature removal from successive copies produced the specific needed parts. This guaranteed identical placement of all holes, as well as other critical lines, curves, and dimensions.
Colors other than red and line thickness bigger than hairline will produce raster engraving, not vector cutting. Different colors can be mapped to raster engrave with differing speed, power, and frequency settings to create reliefs at various depths.
This project relies on vector cutting to create each of the layers.
Step 4: Find a Laser Cutter
- A laser with 120 watts of power should cut through this Acrylic sheet thickness with settings as follows: Speed = 8% Power = 90% Frequency = 5000 Hz.
Make test cuts to be certain of cutting performance.
- Expect to cut somewhere around 7 inches per minute with the above settings.
Doing some rough calculations:
- Rectangles: eight parts with about 64 inches per part equals 512 inches. Dividing the inches by 7 ipm will require about 90 minutes for all the rectangles.
- Holes: There are 128 holes with diameter of 0.23 inches, Using the circumference formula (pi x diameter) we get (3.14159 x 0.23”) = 0.72256” per hole times 128 holes = 92.49 inches. Then divide by 7 ipm results in about 14 minutes for cutting all the holes.
Rounding up, it takes about 2 hours of cutting with these laser settings and this laser’s power and current condition. Also,
consider setup time for the laser.
Find out the laser cost per hour. Get a written quote.
Step 5: Purchase Materials
- Ace Hardware Hillman Item # 44740-E, Aluminum Screw Posts - Brass Plated ¾” long post with screw
- Ace Hardware Hillman Item # 44741-F, Aluminum Screw Posts - Brass Plated 1” long post with screw
- Ace Hardware Velcro Strap part # 90440 36 in x 2 in Velstrap® 2 pack Black 0-75967-90440-1
Alternates may be available depending on which store or chain you visit.
Step 6: Get Your Materials Ready for Assembly
If you're doing the laser setup, keep these things in mind :
- Never mismatch the CAD program canvas size with the laser driver size and expect the cutting to start anywhere except the most wasteful possible place.
- Consider test cutting cheap poster board before starting expensive material cutting.
- DON'T remove the protective plastic from the acrylic until after the next few steps (routing and cleaning).
- Router outside edges of finished parts
Using Amana Tool part # 49492: Router bit type: Radius round over 1/16th radius with ball bearing guide. Set the depth of the router bit so the result of trimming produces a clean round over without any new grooves on the edge being tested.
This does not mean every edge! Only exterior box edges need routing, not layer edges touching each other on same-size layers.
Eight edges need processing:
The top edge of layer 1,
followed by the outside bottom edge of layer 3,
followed by both inside and outside bottom edges of layer 4’s smaller rectangle,
followed by both inside and outside top edges of layer 4’s larger rectangle,
followed by the inside top edge of layer 5,
followed by the bottom edge of layer 8.
... The idea is that you soften the edges of the acrylic where it is exposed .
Wash and dry each part and remove protective film from all Acrylic parts
Step 7: Assembly
- The bottom half of the box using one-inch brass plated posts: layers 4 through 8 (Center, Middle, Middle, Middle, Bottom)
- The top half of the box using three-quarter inch brass plated posts: layers 1 through 3 (Top, Middle, Middle)
- Align all layers and tighten all screws
- Secure both box halves with hook and loop strap
Step 8: Enjoy!
Using one half of the case you can use it to prop open your eReader leather case (as a lap board).
Be sure to put your eReader in the case and close it using the strap to help prevent damage to your reader while it isn't being used.
Step 9: Other Options, and Lessons Learned
Consider cutting this project from very inexpensive Luan plywood for a first experience. Replacing aluminum posts with wood dowels will reduce cost. Test the material of choice for snug fit on the dowels and holes. Wood glue is effective for permanent dowel placement.
It is also possible to laser etch the layers with a raster graphic to customize your case more - add a name or design to make it more personalized.
o Everything has a learning curve.
o Everything always takes longer than you first think possible.
o Acrylic material is an exceptional choice for laser cutting projects.
o Never mismatch the CAD program canvas size with the laser driver size and expect the cutting to start anywhere except the most wasteful possible place.
o Consider test cutting cheap poster board before starting expensive material cutting.