4.7 KiB
Brick Monorail
Parametric Lego-compatible monorail tracks, designed specifically for 3d printing.
Since the parts are made parametric, you can have any length or curve radius you want, but these are the original tracks you can replicate
As an overview, or why it's worth a try: They print rapidly on modern printers, and cost barely anything.
| Name | Material Cost | Print Time |
|---|---|---|
| C15 | ~10ct | 45m |
| C7 | ~5ct | 15m |
| S21 | ~12ct | 1h |
| S7 | ~5ct | 15m |
| S6 | ~5ct | 15m |
| Classic R28 90° Curve | ~25ct | 2h |
| Classic R28 45° Curve | ~12ct | 1h |
| Classic L32 Straight | ~20ct | 1.5h |
| Classic L16 Straight | ~10ct | 45m |
| Classic L8 Straight | ~5ct | 15m |
Todo: ramps, switches, train assembly
Design differences
Injection molding has vastly different requirements to 3d printing. Due to this the original rails print absolutely horribly due to the copious amounts of supports needed. Surfaces printed on supports just never look good.
Because of that, I decided to instead of having a support part on the bottom, I'd carve out space for a 1x2 plate, which you can fit there for the same effect.
The monorail tracks are also solid now, which is not something you can do in injection molding but leaves a really nice surface finish at the bottom of the rail for us.
For now, I also use non-baseplate aligned joints for curves. While this means you can't just snap the rails on a baseplate, it enables you to use straight rails at non-90 degree angles which I think is an absolute win over the original design since the 45 degree curves are useless outside of joining them with switches.
These are 3d printing optimized, compatible rails, not replicas. Replicas print horribly due to support.
Optional Differences
Operating on r25 instead of r28
What difference do these three studs make?
With this radius we can take advantage of the pythagorean triples 3/4/5 and 7/24/25 to stay on the stud
grid with turntables.
- Curve C15
- Curve C7
- Straight S21
- Straight S7
- Straight S6
Two C15 and one C7 make exactly a 90 degree turn, where every part stays on the stud grid.
An s-curve with C7 moves two studs, and can be extended by 1 stud with S7 or 3 studs with S21.
An s-curve with C15 moves over 20 studs, and can be extended by 8 studs with S6 or 28 studs with S21 straights.
Printing
To be compatible with standard bricks, the following print settings are strongly advised
- Nozzle: 0.4, this is equivalent to 1 LDU.
- Layer height: 0.2 will also do. Refrain from using 0.15, since that does not cleanly divides the LDU.
- Make sure your initial layer height is either 0.2 or 0.4!
- Supports: yes, normal, don't use tree supports. what you would call easy for the printer, so be on the lookout.
- Set your "Initial Layer Horizontal Expansion" to a value that works for you, for example -0.2mm to compensate for elephant's foot. Alternatively, you can trim the extra plastic off by hand.
My prints were done on a modified SecKit SK-Go2 running Klipper, with 10k acceleration and 150mm/s print speed for a good balance of speed and quality. A short rail will take about an hour to print.
Filament
| Color | RAL Color | Pantone | PLA Supplier | ABS Supplier |
|---|---|---|---|---|
| Light Bluish Gray | RAL 7040 |
dasfilament | ||
| Light Gray | RAL 7005 |
- None of these colors will be an exact match, just the texture of 3d printing it can make a huge difference, but usually fall close enough in the range.
- The original rails will be in Light Gray, not Light Bluish Gray, but since I barely own any pre- 2004 color change bricks I chose to match my other bricks instead.
Notes for newcomers:
- Most bricks are injection molded from ABS, however I find PLA to be much more easy and safe to handle.
- PLA starts to deform at 60°C, so don't leave it in the sun or in your car.
- PLA is brittle. While ABS deforms with force applied to it, PLA will just snap.
- ABS is harder to print, an enclosure is a must, and warping can be difficult to handle.
Printing Safety
In case you are new to 3D printing:
- Most filaments (including PLA) release toxic gases when burned
- FDM printing can cause fine particle emission
- ABS when heated to normal printing temperatures can release styrene fumes