Depending on the size of the build surface of your printer, you may have difficulty printing a keyguard for a larger tablet. keyguard.scad provides a way for you to break your keyguard design into two parts that you would print independently and then glue together. keyguard.scad tries to be smart about where it makes the cut but it also gives you the freedom to specify exactly where you’d like to make the cut.
Let’s say that you’ve designed a new keyguard and it looks like this:
Unfortunately, when you load the STL file into your slicer, you see that it is larger than your build surface – no matter how you rotate the model.
keyguard.scad can automatically cut a grid-based or hybrid keyguard design into two parts. It chooses a line as close to the center of the keyguard as possible, and between two columns (or between two rows if the keyguard is oriented in portrait mode) to leave you with the largest surface possible to apply your adhesive.
You perform the cut by first choosing, “first half of keyguard” from the “generate” pull-down of the “Special Actions and Settings” category.
A new image will appear that looks like this:
Go ahead and generate the STL file as you normally would.
Now choose “second half of keyguard” from the same menu and a different image will appear:
Again, generate the STL file.
You can also pick your own location to split your keyguard in two. You’ll have to place the split line by hand if you’ve designed a free-form keyguard (where you’ve set the number of columns and/or rows to zero).
You’ll find another option in the “Special Actions and Settings” category called “split line”:
The default value is 0 and can be changed to positive values by sliding the pointer to the right and negative values by sliding it to the left. The best way to understand the effect of changing this option is simply to choose “first half of keyguard” from the generate pull-down and start sliding the block back and forth and watch what happens to the image. If you set the value to zero again, and you’re splitting a grid-based or hybrid keyguard, keyguard.scad will choose a good split location for you.
With luck you’ll be able to fit each of these pieces within the build surface of your printer. Print them as you normally would and then get ready to glue them together. We prefer a two part epoxy for this purpose but you may have success with super glue.
Note that the thicker the keyguard, the more surface area you’ll be able to apply the glue to. Thin points like you might find at the top or bottom of the keyguard due to the exposure of message and command bars may be very difficult to glue and may never come together securely.
Joining Your Keyguard Halves with Dovetails
By default, keyguard.scad splits your keyguard with a simple straight cut resulting in two flat surfaces that can be glued together. As an alternative, you can chose “dovetails”:
Dovetails are often used to join two pieces of wood:
You can see that each part of the joint looks “kind of” like the tail of a bird. Dovetails are used in carpentry to create a very solid and strong joint. You can choose this option to create a strong joint between the two halves of your keyguard, as well:
Dovetail joints work best with rails that are at least 6 millimeters wide but can be used with rails as thin as 4 millimeters. If you choose to split your keyguard with dovetails, you’ll need to choose some additional options:
You can choose the approximate width of each dovetail and how tight or loose the joint will be. The smaller the dovetail gap the tighter the two halves will fit. You may not even need to use glue to attach the halves. On the other hand, you may need a looser joint if your printer over-extrudes a little or is a little less accurate. A looser joint also allows room for glue. Note that adjustments to the tightness affect only the first half of the keyguard so that’s the only part that you need to re-print if you make an adjustment.
The following video demonstrates the effect of these options and why you may need to adjust your app layout measurements when joining your keyguard with dovetails:
Note that in the video the “second half of the keyguard” is reprinted with a smaller gap. In reality, the “first half of the keyguard” will need to be reprinted if you change the dovetail gap.
How to Quickly Determine the Best Dovetail Joint Tightness
It would be slow and expensive if you had to repeatedly print your entire keyguard with different values for joint tightness until you get just the joint you want. You can shortcut the process by printing a small “test” keyguard instead. Follow these instructions:
- Set Tablet Case > have a case to yes
- Set Tablet Case > height of opening in case to 104
- Set Tablet Case > width of opening in case to 100
- Set Grid Layout > number of columns to 0
- Optionally, set Free-form and Hybrid Keyguard Openings > free form keyguard thickness to 4
- Set Special Actions and Settings > split line type to dovetails
- Set Special Actions and Settings > approx dovetail width to 4
- Set Special Actions and Settings > generate to second half of keyguard
- Render/Print
- Set Special Actions and Settings > generate to first half of keyguard
- Render/Print
- If the joint is just right, STOP! Use the current value for tightness of dovetail joint for your keyguard
or
If the joint is too tight, reduce the value of Special Actions and Settings > tightness of dovetail joint
or
If the joint is too loose, increase the value of Special Actions and Settings > tightness of dovetail joint - Go back to step 10