Several measurements are key to producing a keyguard that fits your case and app well. Primary among them are the width and height of the opening in your case. If you don’t get this measurement right, your keyguard will be too large and not lay tight against the glass or it will be too small and slide around on the app – never quite aligning with the images on the screen.
These measurements are notoriously hard to get right just using a ruler. You put one end of the ruler against the edge of the opening and you lay the other end on the top of the case:
Now you have to project the image of the ruler down on to the glass of the tablet and try to guess where the the actual case edge falls on the ruler. It would be better if you could set the entire ruler directly on the glass – a ruler that you could stretch or contract depending on the space it had to fit in.
Easy Measurement Tool (EMT for short) to the rescue!
The EMT is made up of a central compartment with two sliding arms and two bolts on top that can be used to secure the arms when you’re ready to take a measurement.
The STL model files for the EMT can be found here. You’ll also need two M5 x 20 mm screws and two M5 nuts. You can make your EMT even more valuable by putting some ruler tape on one side of the central compartment and something slightly sticky on the bottom (like a healthy coat of clear FlexSeal , a few lengths of electrical tape, some very thin strips of suction tape, etc.) to keep it from sliding on the glass as you pull out the arms. We like the electrical tape solution the best.
(from left to right: 2 layers of electrical tape, thin strips of suction tape, and a healthy layer of clear FlexSeal)
Also, a thin coat of Elmer’s glue helps hold the ruler tape down.
The following video shows you how to assemble your EMT:
Place your EMT on the surface of your tablet. Unscrew the bolts to loosen the arms and pull them out until they span across the opening in your case. Now lightly tighten the bolts until they hold the arms in place:
Next, carefully remove the EMT and place it along side a ruler with millimeter markings:
Look closely at where the far end aligns with the ruler:
You can easily see that the accurate measurement of the case’s opening width is 216 millimeters. You can repeat the process a couple of more times at other places along the length of the case opening. Now, repeat the process to measure the height of the opening.
By the way, I like these metal, metric rulers for taking these measurements and others for your keyguard as well.
There’s another simple measurement that the EMT can take. Each arm has two cuts in their paddles. One cut is a 5 mm chamfer and the other is a 10 mm chamfer. By holding each of these against the rounded corner of the case opening you can get a good idea what the radius of that rounded corner is. If the edges of the chamfer align with the point where the rounded corners become straight then the radius of the corner is the same as the amount of the chamfer:
Here the picture doesn’t do the concept justice but this case has rounded corners with 5 mm radii;
Finally, you can use the EMT to take the measurements of the app without removing your tablet from its case. Set one of the arms to align the “0 mm” edge of the center compartment with the left edge of the screen (or top/bottom edge of the screen):
The x-coordinate of any screen element that’s within 100 millimeters of the left edge of the screen can be read directly from the ruler tape on the side of the EMT:
The x-coordinate of the “came” circle above is 70 mm and the circle is 25 mm wide.
Screen elements further than 100 mm from the edge of the screen can be measured by extending the right arm and then comparing the EMT to a ruler just like you did for the case opening.
Don’t crank down too tightly on the bolts – the arms are just plastic after all – they only need a little pressure to hold securely.
The following video shows the EMT in action on an actual tablet and case:
One Thing to Note When You Print the EMT
The “top” of the EMT has two embedded nuts. If you have fast, dexterous fingers, you can probably get away with inserting the nuts while the part is printing. On the other hand, if your printer (and slicer program) allows it, you should insert a pause in the printing process just before the printer covers the pockets for the nuts:
According to our slicer, if you’re using a 0.2 mm layer height then the last layer (before the pockets get covered) is the 36th layer – at 7.20 mm on the Z axis.
If you to print several of these EMTs at the same time, it can be a difficult to insert the nuts while the printer is waiting for you. We’ve created a simple tool to aid in inserting the nuts and you can download the 3D-printable files from here.