Keyguard frames are used in two different ways – as a screen protector or as a rigid frame for easily and quickly swapping keyguards or flipping-up the keyguard.

Keyguard frames work in conjunction with a keyguard to fill the space of the case opening.  The keyguard fits within the keyguard frame.  The “mounting method” options apply to the keyguard frame (click on an image to enlarge it):

no mount
clip-on straps	shelf
slide-in tabs	raised tabs

The keyguard mounts within the frame using either snap-in tabs (for quickly inserting and swapping keyguards) or posts (for a flip-up keyguard) (click on an image to enlarge it):

snap-in tabs	posts

 

Screen Protectors

Tablet cases often include screen protectors.  Based on its name, you’d think the purpose of the screen protector is to protect the screen from scratches and breakage.  However, most tablet screens are very resistant to scratches, and any force strong enough to crack an “unprotected” screen will probably crack a “screen protected” screen.  What the screen protector is more effective at doing is preventing liquids that have dripped onto the case from reaching the electronics of the tablet inside.  This is done by sealing a thin sheet of transparent plastic to a thick, rigid frame.  The plastic sheet and frame act like a shallow bowl to hold any liquid dripped into it. 

Screen protectors have long been the bane of keyguards because the opening in the screen protector’s frame is often only slightly larger than the tablet screen. 

In order to expose as much of the screen as possible, the keyguard must have a very thin perimeter.  This makes the keyguard more fragile and greatly limits the mounting options.  The thin perimeter means there’s very little plastic for the attachment of micro-suction tape.  The rigid frame means that you can’t wedge the keyguard into place.  Finally, the clear plastic sheet is sealed to the frame, so you can’t insert slide-in tabs under the edge of the frame.  You’d first have to break the seal on the screen protector and that would void any implied warranty offered by the case manufacturer.

We’re going to look at how we might replace the screen protector that came with your case with a 3D-printed version where you can control the size of the case opening so that your keyguard can have a thicker perimeter.  And there might be additional benefits.

This method can also be used to create a screen protector for a case that didn’t come with one.  Either the case came with a rigid frame that doesn’t have a transparent sheet of plastic attached, or the case has no rigid frame at all.

The idea described on this page came from Felice Flowers.  She wondered if it would be possible to replace the screen protector with a 3D-printed version designed to accept a fitted keyguard.  And would it be possible to attach a sheet of transparent plastic to the underside of the custom screen protector? 

It turns out that you can – and the result is quite satisfactory.

The following example is for a particular case and screen protector combination.  Your screen protector may be very different in its design and you may need to take a different approach all together.

Taking a close look at a commercial screen protector

A screen protector normally attaches to the face of the tablet with some retainer clips built into the underside of the rigid frame:

Then the combination of screen protector and tablet slide into a rubbery case that protects the edges of the tablet if dropped.

There’s no way to replicate these clips reliably with a 3D-printed replacement so we’ll look at different methods to mount the keyguard frame to the tablet.

Designing the Screen Protector

Our screen protector needs to fit within the same opening as the original screen protector.  The most accurate way to get these measurements is to measure the original screen protector directly.  The outer edge of the rigid frame should match the opening in the rubbery part of the case, which includes the curvature at the corners:

Place these measurements in the “height of opening in case”, width of opening in case”, and “case opening corner radius” fields of the “Tablet Case” section:

These will be the outer measurements for the keyguard frame.

We’ll now set temporary dimensions for the keyguard that will snap into the keyguard frame.  We’ll use the internal measurements of the screen protector for this:

Enter these measurements as the “keyguard height, width, and corner radius” measurements in the “Keyguard Frame Info” section and set “have a keyguard frame” to “yes”:

The corner radius is hard to measure – it could be as small as 0 mm – but we’ll just set it to 1 mm for now.  We may need to adjust all these measures as we go along.

The keyguard now looks like this:

The “cross-like” thing on the bottom edge of the keyguard (actually on all edges) will snap into recesses in the keyguard frame.

We can see what the keyguard frame looks like at this moment by setting “generate” to “keyguard frame” in the “Special Actions and Settings” section:

This actually looks pretty good,  The home button opening and camera opening are well away from the edge of the opening for the snap-in keyguard.  That means there will be plenty of surface area in that region to securely attach the plastic sheet.

If the top and bottom edges are too thin or if you need to put more space between the opening for the keyguard and the camera and home button openings, just reduce the “keyguard width” and/or “keyguard height” settings in the “Keyguard Frame Info” section.

For example, maybe we’d like to see the top and bottom edges a bit wider.  We can make them a little wider – hopefully, without taking too much away from the keyguard by reducing the “keyguard height” to 120 mm.  There’s no hard and fast rule here.  The frame now looks like this:

When making these adjustments, go back to the view of the keyguard (set “generate” to “keyguard” in the “Special Actions and Settings” section), to ensure that you still have a viable keyguard design and you haven’t made the edges too thin.

Mounting the Keyguard Frame

One way to fit the frame into the case opening is to put a shelf around the outside of the frame.  Set “mounting method” to “Shelf” in the “Mounting Method” section:

You can control the thickness of the shelf and the depth of the shelf in the “Shelf Info” section of options.  You can take these measurements directly from the screen protector that came with the case (“shelf thickness” shown below):

There are several other options for mounting your keyguard frame to the case: slide-in tabs, raised tabs, and clip-on straps – but among these, you’ll probably go with slide-in tabs.

Set “mounting method” back to “Slide-in Tabs” as the mounting method in the “Mounting Method” section.  Use the settings in the “Slide-in Tabs Info” section to control where the tabs go, how wide they will be, how far apart they will be, and how thick they will be.  In this example, we’ve put tabs only on the vertical sides.  They’re 1 mm thick, 3 mm deep, and 96 mm wide.  By setting the distance between them to a negative 10 mm, we can make them overlap and behave as a single tab:

 

Both the shelf and the wide, slide-in tabs provide a good amount of surface area for attaching a transparent sheet of plastic to the underside of the frame.

Now set “generate” back to “keyguard” and design your keyguard as you normally would based on the app and grid layouts. 

Case Additions

You can put instructions into the “case_additions” data structure to add more plastic to the outside edge of your screen protector – or cut openings into the screen protector by putting instructions into the “case_openings” data structure. 

One thing to note is that the 0,0 location is now in the lower right corner of the raised part of the screen protector:

This case has a small “crescent moon” cut-out for the home button.  We want to fill in this space with plastic to protect the tablet as much as possible:

We’ve added the following instruction to the” case_additions” data structure:

Since we’re measuring relative to the lower left corner of the raised portion of the case opening protector, half-way up the left side is calculated as 127/2 = 63.5.  (The case opening – and keyguard frame – is 127 mm high.)

This instruction has the following impact on the perimeter of the screen protector:

You can learn more about adding case additions and case openings by following their respective links.

The keyguard frame is now ready to print, and the transparent film is attached.

Attaching the Plastic Sheet

Most rigid plastic sheets will probably work, though you should avoid films that are intended for putting in a laser or inkjet printer.  Such films have a coating to help the ink adhere, which reduces the transparency of the film.  Here’s one transparent plastic sheet that will work.

The attachment of the keyguard frame to the plastic sheet needs to be waterproof or your screen protector won’t achieve it’s primary function.  You could try using glues or silicon caulk, but spray adhesive works very well and is easier to apply.

Begin by putting masking tape around the keyguard opening in the frame.  Avoid putting any tape on the underside of the frame.

When spraying the underside of the keyguard frame, try to spray directly downward rather than at an angle.  That will limit the amount of adhesive that will get on the face of the frame.  

While the adhesive is still tacky, turn the screen protector over, and set it onto the sheet of plastic.  Place a book or other heavy item on top to ensure a good seal between the protector and the plastic sheet.  Allow the adhesive to dry.  When dry, you can remove the masking tape.

This video illustrates the process of mounting the screen protector to the plastic sheet:

Testing the Screen Protector

The following video follows a screen protector that has been assembled as described above and has had water (with a pink dye) poured onto its surface:

After 20 minutes, there is still no water leakage from around the edge of the screen protector.  If you dump any liquid off of the screen protector within a few minutes of the accident, your tablet should be perfectly safe.

Preparing the  Screen Protector for Mounting on the Tablet

Once you’re confident that the adhesive has dried, you can use scissors to cut along the edge of the screen protector to remove all the excess plastic sheeting.

It has to be possible to depress the Home button, so you’ll use a “sharp” utility knife to cut a circle in the plastic sheet around the Home button opening.

Our example screen protector doesn’t have any clips on the bottom so we’ll need to find a different way to mount the screen protector securely to the tablet.  Micro-suction tape does this job very well. 

You won’t be removing the screen protector from the tablet except very rarely, so you can feel free to add a generous amount of micro-suction tape.  Tape should be applied to all four sides of the screen protector bottom.:

The transparent film is still in place on the tape in this photo.

This is a good time to clean the glass of the tablet – while you still have easy access.

Note that the micro-suction tape holds VERY well so position the screen protector very carefully as you make the attachment.  Watch carefully as you mount the screen protector to the tablet – especially ensure that the camera is centered in the camera hole.

Another option is to use masking tape to hold the screen protector/keyguard frame to the tablet.  You’ll need to add enough tape so you can wedge the pair into the case (which can be a struggle) without the two separating.

These small nylon pry bars can come in handy to work the shelf or tabs under the edge of the case opening!

Mounting the keyguard within the keyguard frame

By default your keyguard is mounted inside the keyguard frame by a set of snap-in tabs.  Using this approach, you can easy swap between several keyguard layouts as you switch between different tablet apps.  Under certain circumstances you may want to eliminate the snap-in tab from the top or bottom edges of the keyguard.

Alternatively, you can mount the keyguard using posts.  Using this approach, you can swing the keyguard out of the way temporarily to interact with your keyguard in a way that would have otherwise been hindered by the keyguard.

Snap-in Tabs

Your keyguard will include snap-in tabs on all sides that “snap” into recesses on the inside edges of your keyguard frame.  The tabs are designed to resist sliding the keyguard around on the tablet face, and to resist pulling the keyguard out.

snap-in tab on the outside edge of the keyguard	snap-in tab receiver on the inside edge of the keyguard frame

You will need to pull the keyguard away from the edge of the keyguard frame slightly when inserting and removing the keyguard.  You can follow the same process to easily swap keyguards designed to fit in the same frame.

If you have a keyguard design that doesn’t reach all the way to the top of the frame, you should set “snap in tab on top edge of keyguard” to “no” in the “Keyguard Frame Info” section.  If you don’t, you’ll have a free-floating snap-in tab in your model that you’ll have to remove in your slicer or you’ll have printing problems.

Every 3D printer is different.  Unless you’ve gone through a lot of work to tune your printer, it may under or overextrude plastic.  If the keyguard is too difficult to squeeze into the keyguard frame or it’s too loose and slips out of the frame too easily, you can make small adjustments to the overall size of the keyguard.  There are two sliders in the “Special Actions and Settings” section called “keyguard horizontal tightness of fit” and “keyguard vertical tightness of fit”.  A value of 10 increases the horizontal or vertical size of the keyguard by 1 mm.  A value of minus 15 decreases the size of the keyguard by 1.5 mm.

Posts

Mounting your keyguard to the frame with posts will allow you to flip the keyguard up and out of the way temporarily and then flip it back into place:

This is controlled by two options that are also in the Keyguard Frame Info section.

If you set the “mount keyguard with” option to “posts”, your keyguard design will be modified automatically.  It will be trimmed down at the top to the bottom of the upper command bar and a pair of posts will be added.

Slots for these posts will be created on the underside of the keyguard frame to accept these posts.  The diameter of the posts and the diameter of the slots will match the thickness of the keyguard.  If the keyguard and the keyguard frame have the same thickness, the slot will break through to the top surface of the frame.  If that should happen, just increase the thickness of the frame or decrease the thickness of the keyguard:

5 mm frame and 3 mm keyguard	5 mm frame and 4 mm keyguard
5 mm frame and 5 mm keyguard	6 mm frame and 5 mm keyguard

The ease of rotating the keyguard within the frame will depend on the tightness of the fit between the posts and the slots.  This is difficult to predict, given the large variance in different 3D-printers and slicer settings.  If you don’t like the amount of force required to rotate the keyguard or if you’d like more friction to keep the keyguard up in the air, change the value of the “post tightness of fit” option.  Larger values make the fit tighter, and lower values loosens the fit.

Splitting Your Keyguard Frame

You may find that you can’t fit the keyguard frame on your printer.  In that case, you can split your keyguard frame into two parts by choosing “keyguard frame – split” from the “generate” pull-down in “Keyguard Basics”.  The two parts will automatically be relocated to fit as tightly together as possible:

If you move the split line to the left or right, you may be able to use dovetails to split the keyguard and join the two parts more easily:

You set the location of the split and the type of split by setting the values of “split line location” and “split line type” in “Special Actions and Settings”.

The two parts of the keyguard frame will be arranged to accommodate the relative length of each part.

Mounting Your Keyguard Frame and Keyguard

Slide the screen protector and tablet into the case, add the keyguard, and test it out…

Repeating what I’ve said already…  These small nylon pry bars can come in handy to work the shelf or tabs under the edge of the case opening!

Some Screen Protectors can’t be Replaced.

You may come across a case with a screen protector like this one:

The light blue screen protector of this case is critical to holding the entire case together by clipping to other parts of the case.  As mentioned earlier, there’s no way to recreate these critical clips using 3D-printing.