Possible to laser engrave PBT keycaps?

[Erik Olson]

There are 2 methods used to make letters on keycaps: engraving + infilling, and UV marking.

Industry uses a UV laser to alter the color on keycaps.

Video of production line Lasering the keycap labels:  http://i.imgur.com/goLoYFh.gifv

This WIKI on all the processes doesn't say much about engraving

https://www.reddit.com/r/MechanicalKeyboards/wiki/keyboard_and_key_manufacturing#wiki_lasering_printing

Question is: is PBT safe to engrave on our CO2 laser?

(PBT is the common keycap material)

[José Hiram Soltren]

So, I'm a keyboard guy, not a laser guy. Matt Mancuso should chime in here. I've not used the ATXHS lasers but I've used other lasers.

My answer is "it's probably safe but I don't want to sign off on it." Usually when we can't laser something it's because of some particularly toxic or corrosive side product. Like PVC (chlorine) or ABS (cyanide).

Given that PBT, "polybutylene terephthalate", is just a long chain of carbon, hydrogen, and nitrogen, it ought to be safe. Of course I can't speak to any additives. https://en.wikipedia.org/wiki/Polybutylene_terephthalate

PBT isn't on this list: http://atxhackerspace.org/wiki/Laser_Cutter_Materials

Trotec specifically says PBT is okay. https://www.troteclaser.com/en-us/knowledge/faqs/laserable-materials/. But they say the same thing about ABS...

This discussion implies that PBT is a widely laser etched material: https://www.sciencedirect.com/topics/materials-science/laser-marking (links to paid content).

This manufacturer lists PBT as a safe to etch plastic along with POM and others: https://www.ensingerplastics.com/en-us/shapes/plastic-material-selection/laser-marking

A keyboard manufacturing friend tells me that PBT is safe to etch but that you need additives in the plastic to control the color of the etching (darker, lighter, etc).

I post as "XMIT" on some of the keyboard forums (deskthority.net, geekhack.org, keebtalk.com, reddit.com/r/mechanicalkeyboards).

--José

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[José Hiram Soltren]

Oh: assuming it's okay, then I'd worry about fixturing, and dealing
with the fact that many key caps have tops that curve in one if not
two dimensions by up to about 4mm. Is this within the focal range of
the red and blue lasers?

I made this stand ages ago but can't find the files. D'oh! It's just
two sheets of acrylic, about 30 minutes on the laser. This would be
great for fixturing the PBT keys of your choice.

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[Isaac B]

If you're doing SA rows 3? or DSA caps they will at least be fairly flat in the center.

You can mount them to switches on a switch tester or mod station as a fixture, example below.

If you don't have one, then you can make one of these out of acrylic with the laser. :)

I'm having trouble finding info about laser safety of PBT plastic, though.

When we find out the answer, get sign off from Danny/Rob and please add it to the wiki.

http://atxhackerspace.org/wiki/Laser_Cutter_Materials

Absolutely DO NOT DO THIS with ABS caps.

Isaac

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<IMG_20191127_103641.jpg>

[José Hiram Soltren]

From this MSDS: http://www.aectra.com/wp-content/uploads/2015/08/PBT-SDS-rev3-05_2015.pdf

10.6. Hazardous decomposition products:
Thermal decomposition will yield oxides of carbon and/or acetic acid and aldehydes.

So, CO, CO2, vinegar, and ... maybe formaldehyde?

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[Matt C.M.]

I'm not sure about pbt, if Danny oks it for use on the laser, some testing for sure should be done. Some materials just don't behave well under lasers of the wrong frequency. I wouldn't be too worried about the curvature, though if you're doing angled top keys, it would be worth making a jig to hold them so the top is flat. The focal length of the laser lenses is 2", a difference of a couple mm isn't the end of the world for engraving.

[José Hiram Soltren]

I chatted with a friend who runs a keyboard company. He recommends
against lasering PBT since you don't always know what additives are in
there. Says industrial PBT lasering is often done on fiber lasers.

It's helpful to get an MSDS for the exact material you're using so you
can tell what the combustion byproducts are. This is equally true for
POM, which is generally a laser etch friendly material.

I reached out to Universal directly, haven't heard back yet. Maybe
I'll hear back next week?

On Thu, Nov 28, 2019 at 7:42 PM Matt C.M. <mcma...@gmail.com> wrote:
>
> I'm not sure about pbt, if Danny oks it for use on the laser, some testing for sure should be done. Some materials just don't behave well under lasers of the wrong frequency. I wouldn't be too worried about the curvature, though if you're doing angled top keys, it would be worth making a jig to hold them so the top is flat. The focal length of the laser lenses is 2", a difference of a couple mm isn't the end of the world for engraving.
>

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[Martin Bogomolni]

I would recommend against the engraving of PBT unless you know it is pure and free of additives.  Keycaps tend to have all sorts of colorants, hardeners, and other additives... 

A fiber laser would be a better choice for this type of work and marking.

YMMV

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