print.md

Printing advice

Some parameters are intended to aid manufacturability. This includes the supported parameter, which is intended to reduce the need for building supports in slicing software.

Orientation

With single-head FDM printing in a material like PLA, a relatively simple way to get a good result is to print each key in an upright position, with supported. In general, a minimal-style cap with a tall top plate (hence a vaulted ceiling) should need no further support and no brim.

Consider the main alternative for FDM: Printing each key upside down. This will often give you a cleaner stem and skirt, but if the face of the key is not even (i.e. bowl-radii is not nil), cleaning up the print will be more difficult. In particular, even with fairly dense supports added by a slicer, you will probably find cavities behind the face to such a depth that a really good surface finish is hard to achieve. Still, if you intend to paint your prints anyway, or if you have a dual-head printer with a soluble support material, printing upside down may ultimately be a better option.

For SLA printing, try rotating the cap and adding supports in your slicer to drain excess resin away from the tip of the stem on the cap.

Cleanup

If you’re using supported and printing in an upright position, you will need to remove the supports. The recommended way to do this is with a pair of flush cutters, working gradually through a series of small snips.

Minor details of a bad FDM print can be improved with a soldering iron set to low heat. For PLA, try 150 °C (300 °F). Work in a well-ventilated area and do not waste good soldering tips on plastic; prefer tips that are already old and oxidized. Apply to narrow stems to strengthen layer adhesion or fine-tune dimensions. Apply to legends to clean up smudged contours.

For help sanding keycaps to the desired finish, use the jig mode.

Troubleshooting

Recommended solutions to common problems.

The stem is too thick

Check general printer settings and try running dmote-keycap with error compensation.

• For an :alps keycap where the stem is too thick to fit inside the the switch, run with --error-stem-positive 0.1 or more.
• For an :mx keyp that does not fit over the cross of the switch’s stem, run with --error-stem-negative -0.1 or less.
• For an :mx-rect keycap where the stem does not fit inside the switch as it descends on the spring, run with --error-stem-positive 0.1 or more.

The cap is too narrow when printed

Check general printer settings and make sure your prints are properly cleaned. If the first layer of the skirt has an inward lip to it, that means your nozzle was too close to the print bed; trim that lip with a hobby knife.

If the problem persists, there are two parameters you can tweak:

• --skirt-space puts the skirt further away from the switch and leaves it intact.
• --error-body-positive, when set to a negative value, creates a block of negative space around the body of the switch, following the shape of the switch itself more closely than --skirt-space.

The former parameter describes the ideal shape. The latter describes a common printer behaviour, not the ideal shape. The negative space created by the error parameter eats the skirt from the inside, specifically to compensate for printer inaccuracy.

The two parameters do not interact with one another, nor with --skirt-thickness. If --skirt-space is much larger than the error parameter, the error parameter will have no effect. If, on the other hand, the error parameter is set to such a negative value that it does have an effect on the skirt, you may need to compensate by raising --skirt-thickness. Notice that extra skirt thickness, in turn, can cause neighbouring keys to collide.

Finally, the two parameters work on different scales and in different directions. Decrementing --skirt-space by 1 brings skirt and switch 1 mm closer on every side, which decreases the width of the keycap by 2 mm on each side. Decrementing --error-body-positive by 1 removes 0.5 mm from the inside of the skirt, if there is no gap at all.

In general, if you want keycaps that are truly minimal, set --skirt-space to zero and --error-body-positive as close to zero as the quality of your printer will allow. If instead you prefer good-looking prints with even wall thickness, sacrificing key density, set --error-body-positive to zero and raise --skirt-space until your prints are no longer too narrow.

The cap shrinks after printing

If exposed to sunlight, even through a window, PLA can get hot enough for annealing to occur. This can warp a keycap, making it too thin in one dimension. Observe advice above for narrow caps, or print in a material that will not warp where you intend to use it.

The cap comes loose while printing

Use standard techniques for print bed adhesion with your printer and filament. For FDM this means e.g. glue stick, isopropyl alcohol, bed heating, precise z-offset tuning, extra first-layer height and extrusion width, brim etc.

If that does not help, or if the caps you are printing do not have the skirt and stem going to the exact same level, run with --supported or have your slicer generate supports.

If that still does not solve the problem, try nozzle lifting in your slicer. In PrusaSlicer v2.6.0, for example, go into “Printer settings” → “Extruder 1” → “Retraction” and set “Lift Z” to a positive value so that the printer lifts before moving between stem and body, reducing shear. If the setting is at zero, try 0.2 mm.

The stem bends while printing

Use standard techniques for print bed adhesion, and run with --supported.

Also try --horizontal-support-height 2 or more. This makes taller buttresses that stabilize the stem by connecting it more strongly to the skirt. You will need to snip these off with flush cutters, which gets harder the more you increase the value.

The top of the cap is not smooth and solid

For detailed but fairly solid objects like keycaps, it is important to trim in slicer settings for filling space. With a completely solid test model such as an 8 mm cube at 100% infill, check that your material’s extrusion multiplier, print line width (a.k.a. extrusion width) and infill-to-perimeter overlap all work together to produce a solid object without gaps or external blobs.

Use ironing in your slicer, with little or no extrusion, to smooth out each layer of the top face before adding the next.

Legends are hard to read

Nozzle size in FDM printing is a fundamental limitation to horizontal resolution. You can work around this a little bit by tweaking slicer settings. In particular:

• Use reduced extrusion width and ironing.
• Use variable layer height. Reduce the very top layers to the minimum your hardware can handle.

When you know what you can achieve this way, design your legends for your hardware or apply negative --error-top-negative/--error-side-negative. Make your figures thick enough that they survive slicing and printing with the amount of manual cleanup you want to do.