Flaps for split flap displays
Generate your own flap set as PDF and 3MF in the Flap Maker.
The flaps are what makes a split flap display — split flap. Each module uses a full set of flaps mounted on a drum, flipped by the stepper motor to show the desired character.
There are three ways to get them, and they're all valid:
| Route | Material | Thickness | Good for |
|---|---|---|---|
| 3D print them | Multicolor PLA | 0.3–0.6 mm | Anyone with a multicolor printer. Free files below. |
| Have them printed | Plastic sheet, e.g. PP | 0.3–0.6 mm | Custom alphabets, other languages, larger runs, colour flaps |
| Buy a set | — | — | Getting going without a printer or a print shop |
Two things are fixed whichever route you take. Flaps are 44 × 30 mm plus material for the hinges, and they finish at 0.3–0.6 mm thick. The hardware design is built around both, and the thickness is what lets a flap flex.
Alphabet
Each standard set of flaps contains 43 characters, set in the typeface Oswald:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
€ 0 1 2 3 4 5 6 7 8 9 . ? ! - : [blank]
The last character is a blank flap — when the drum rotates to this position, the display appears empty.
How many flaps a drum needs
| Flaps | |
|---|---|
| Minimum for reliable operation | ~30 |
| Standard set | 43 |
| Maximum tested | 52 |
The minimum surprises people. The topmost flap needs pre-tension to fall cleanly, and it gets part of that from the other flaps being there. Below roughly 30 the mechanism becomes unreliable, so if your display only needs ten characters or six colours, repeat the set until you're above 30 rather than running a half-empty drum.
52 is the highest count I've built and tested. It can probably be pushed a bit further.
One alphabet for the whole display
It's tempting to give each module only the letters it needs. The third module only ever shows five different characters, so why print 43?
Don't. Identical alphabets make every module interchangeable: positions can be swapped, and a spare fits anywhere in the display. Give each module its own flap set and a failure means rebuilding that specific drum instead of swapping in the spare you keep in a drawer. The saving is small, the cost when something breaks isn't.
Custom alphabets
The firmware doesn't care what's on your flaps. Homing works by asking which character is currently visible, so any custom set works: other languages, symbol sets, logos, colours.
You can build and preview a custom alphabet on play.flipforward.de before committing to a print run. Alternative alphabets are supported there, and a virtual twin behaves exactly like a hardware display, so what you see in the browser is what you'll get on the wall. If you need the cut and print templates for a print shop, ask on Discord or by mail and I'll send them over.
Colour flaps and pixel displays
A module doesn't have to show characters. Fill the drum with solid colours and each module becomes one large mechanical pixel. A grid of them renders low-resolution images and animations.
Stay above the 30-flap minimum. With six colours, print each colour five times. The repetition isn't waste, it's what makes the mechanism work.
It also makes the display fast. With five copies of every colour spread evenly around the drum, the nearest instance of any colour is never far away, so a colour change lands in well under a second. A 43-character alphabet can't do that.
3D printing flaps
Flaps can be printed at home on any multicolor-capable 3D printer. I've used PLA and that worked very well so far. The files are split across three plates; each .3mf contains the geometry for multiple flaps. Make sure you import them as a multi-part object, not as separate objects — otherwise they'll just fall down to the build plate and not, well, work.
Filament Assignment
The .3mf files do not include filament presets — you need to assign the correct filament to each object in your slicer. Each flap consists of three parts:
| Object name | Filament |
|---|---|
*_base | Black |
*_front | White |
*_back | White |
In your slicer, each object will show up with a name like f00_base, f01_front, etc. — assign the filament slots accordingly.
Print Settings
Getting the right layer height is critical — each printed flap needs to end up at a total thickness of 0.3–0.6 mm. If the flaps are much thicker, they won't flex, and that will lead to poorer overall function. It's imperativ that the flaps are thin. If you have issues that the white is bleeding through black layers, try tuning your flow rate or changing the filament.
| Setting | Value |
|---|---|
| Layer height | 0.15 mm |
| Print type | Multicolor |
Make sure your first layer is well calibrated. Since the flaps are so thin, even small deviations in the first layer will have a noticeable effect on the total thickness.
Flaps from a print shop
If you need an alphabet the printed files don't cover (another language, a custom symbol set, brand colours) a print shop is the way to go. This is how the flaps on the finished displays are made.
Material and thickness
Polypropylene works well, at the same 0.3–0.6 mm as a printed flap.
Getting this wrong is the most common mistake. A 1 mm sheet feels reassuringly solid and is exactly wrong, because the flaps have to flex for the display to work reliably. Thin and slightly floppy is correct.
Printing method
UV printing and screen printing both work. The awkward part is the colour rather than the process: white on black is hard to source, and plenty of shops will quote for it and then struggle to deliver good opacity. Ask for a sample before ordering the full run. A scheme that runs dark on light is much easier.
Cutting
The outline trips up most quotes. Die punching is the traditional answer and gives clean hinge cutouts at volume, but tooling costs money and shops are often reluctant for small runs. Laser cutting works well for a one-off installation, and it's what I'd try first if a die punch stalls the schedule.
Send the shop the cut and print files rather than a description. Ask on Discord or by mail and I'll send them.
Budget the time
Flaps are the slowest manual step in a build. The module itself goes together quickly. Assembling and mounting a set of flaps takes roughly five minutes per module and doesn't get much faster with practice, so a 30-module display means a couple of hours of flap work. It's also the part with the longest lead time, so plan the print run early.