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  1. #1

    "Double-shot" SLA sort of

    I would like to make some custom size keycaps, and would like the legend to be embedded in the cap (not painted on).

    FDM printers can use two extruders, but I don't think they have the resolution. The Prusa i3 MK3S with multi-material might be able to do it with a 0.015mm nozzle.

    I am told that SLA or SLS is the way to go, but that gets me one color. Would it be possible to print a keycap with the a negative-space legend (not sure how to describe it). A hole left behind in the shape of the text.
    The idea being to manually pour a different resin in later? Would it even cure?

    Is there a better process?

    I'd like quality that approaches injection molding. And a legend that doesn't wear off easily.

  2. #2
    Your approach is sound. You won't find a 0.015 mm nozzle, but maybe a 0.15 mm nozzle, but it's still an FFF process. Resin will get you a decent resolution and maybe a bit of brittleness. SLS is going to be much stronger and more durable.

    Negative space (debossed text) with a resin fill is probably the right direction. If you mix the resin properly, it will cure without complications. I have UV curing glue that might be able to be tinted then cured with a UV light. It's astonishingly strong and durable.

    If the cap has a flat top and the debossed text is printed to match, each letter or shape could be inlaid with adhesive. It's likely to be tiny and difficult to manage, of course.

  3. #3
    Thanks for the prompt reply! I'm probably misreading things.

    Here is one source of information:
    I saw the table of nozzle sizes, and interpreted min layer height. I have no idea what the x-y resolution would be. The author mentions using a Prusa machine.

    But 20-50 micron resolution (if I read it correctly) sounds like a much nicer result.
    But I also read that FDM can be sanded and polished afterwards. With the amount of work I'm committing to, a bit of sanding doesn't sound bad.

    A translucent material for filling the debossed region might give me a nice effect with led backlight.

    I don't have a printer now, so am doing a lot of window shopping. I need to know what is possible before committing to a technology.
    I still haven't settled on FDM vs SLA vs SLS.

  4. #4
    Some readers here will recognize that I'm a proponent of the Prusa MK series. The kit is a joy to build, with documentation unparalleled in the world, supported by online resources to match. It's probably the most reliable printer I've ever used, in a public makerspace (public library) with wonderful flexibility in terms of material, mods and features.

    The link you provided was interesting reading, confirming the 0.15 mm nozzle size, associated with a minimum 0.04 mm layer thickness. If I had to print that thin, I'd certainly pick a Prusa MKx on which to do it. The x/y resolution is going to be between 1.5 and 2.0 times the nozzle diameter. Even at the 2x level 0.30 mm resolution is pretty good. I've printed a key cap at 0.10 mm layer thickness, probably 1.5 mm x/y resolution. I never heard back from the recipient regarding his satisfaction, nor regarding durability.

    ABS sands to a high sheen, fairly reflective as does PLA but one must be careful to not overheat the PLA. Wet sanding addresses that problem, of course. Micromesh is an amazing (and pricey) tool for that task. When it contacts one's thumbnail in the process, you have polished nails to match your local salon, although only one.

    For your selection of printing types, SLS is going to be farmed out, unless you want to invest mid-four-figures. I'm hoping to purchase a Prusa MK3 of my own in the not-so-near future, as I don't have a workspace on which to place it just yet. My current foray is in the world of MSLA, which is a bit more challenging than filament stuff. FDM is brand specific (Stratasys), while FFF is generic. Kleenex versus facial tissue. -Semantics.-

    A few types of filament and resins are nicely translucent and would perform as you suggest for internal lighting. The trick would be getting the debossed section open to the underside, which would create a non-manifold object impossible to print. Post-processing with removal tools may be the only option for that sort of result. Maybe add the translucent fill with a good adhesive or resin, cure it, then carve away the light-blocking portions.

  5. #5
    If was going to use FFF, I would use a dual extruder. Prusa has a multi-material upgrade for another $300, but I haven't heard much about how well it performs. What I have seen are huge purge blocks, with what seems to be 50% waste of material. I'll be looking hard at other options.

  6. #6
    Super Moderator curious aardvark's Avatar
    Join Date
    Jul 2014
    lol ask autowiz about the prusa mmu - 'total nightmare' would be how i describe his experience.

    forget sls - that's $10,000 absolute minimum.

    A resin machine using 'tough' or 'flexible' resin would be your easiest bet.

    depending on the file, wall thickness, text size etc.
    an IDEX fdm machine could probably do it.

    Using 0.15mm nozzles - not easy to use and be prepared for it to take 4-6 hours per key cap.
    personally I don't believe that any current fdm printer can reliably pull of sub 0.05mm layers.
    though if you were going to do it - then a teeny tiny nozzle diameter would probably help.

    what sort of actual sizes are you looking at ?

  7. #7
    Sizes are pretty normal 1u (around 18x22mm), 1.25, 1.5, 1.75, 6.

    I don't mind the time. I need 120 in various sizes, with different debossed text.

    IDEX printers are a bit spendy. Could a dual extruder match the quality if it took longer, and perhaps had something to wipe the nozzle with?

  8. #8
    I use a Sigma R16 IDEX printer, which has a silicone rubber nozzle scraper, but when printing in two colors, there's still some "dribble" to address. For that, I use what Simplify3D calls an ooze shield. The parameters are adjustable, but I'll use two nozzle widths, one for each color. Not much waste, especially compared to the purge tower, which is not warranted for an IDEX machine. I've printed 0.10 layer height, but would not attempt 0.005 with my current 0.4 mm nozzle diameter. If BCN3D wasn't so expensive for nozzle changes, it would be worth a try to use a smaller set.

  9. #9
    If it was my project I'd do it on my resin printer - I usually print at 0.05 on it but I -think- it will go lower than that. White resin and use a different UV resin for your embossing, with a UV pen to cure then post cure the whole lot together.

  10. #10
    Super Moderator curious aardvark's Avatar
    Join Date
    Jul 2014
    conventional side by side, dual extruder machines are just more trouble than they are worth.

    nozzle wiping is a bit pointless as it would always wipe both nozzles. removing filament from the one currently being used to extrude.

    And no matter how carefully you calibrate them - it doesn;t take much for the nozzle not in use to catch a part of the print.

    Since i switched to top mounted spool holders on the knp I just use the right nozzle.
    I can still have two filaments ready to go - I just feed both into the right nozzle when i want to change.

    But it's just an awful lot of hassle to use both on the same print.

    Given that a decent idex can be had for less than $500 and a decent dual extruder is going to be similiar oir more. Idex is now very much a good and viable alternative.

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