Laser Etching Painted Plastic


#61

Possibly but that is really not the problem here. The Zing has plenty of power/speed range to adjust things down to get it to just engraving through the Black. I wouldn’t spend much time trying to increase reflectivity of the White layer because that probably also means a reduction in light transmission through the white paint. That (and getting a good even coat to avoid spackling) is where the real problem has been.

The first step is to experiment with the White paint layer using various degrees of thinning, # of layers, spray nozzle, etc. and then see what it looks like when illuminated from the back. When I find the right combination to get even and proper illumination, then I can move on to tweaking the Laser engraving power/speed settings to just engrave through the black.


#62

Yes it is an exercise in trial and error. Have you tried using the gradient feature with the laser to narrow down the power range that’ll shave off the black but leave the white layer behind?


#63

No I haven’t. However, like I said, the laser engraving is not a problem. The Zing does this very nicely and produces good results. I don’t see a need to try to tweak what is not really broken. The real problem I’m having is painting the clear acrylic (after bead blasting to give it a frosted look) of the Light Plate with the White Acrylic paint (suitably thinned) so that when it is back lit, there isn’t a spackled, grainy appearance and I can get an even 1 -2 Lumens light through the plastic.

That is where all of my experimentation needs to take place. In other words, I’m dealing with a paint/painting/light transmission problem here and not really a laser engraving problem. And just to be clear, the paint and techniques I’ve used in the past produce good results for 95% of most peoples needs. I’m just a perfectionist and I’m trying to come close to the MIL-SPEC LPs.


#64

Very informative, thanks for the info!

A few questions if I may.

Why must you paint the bottom of the acrylic white also?

How does the copper heat sink work exactly? I don’t understand why such a small piece of of thin copper makes any difference.

What is the purpose of the “special translucent laserpaint”?. I imagine it’s to protect the white layer underneath from the laser, but how can it be translucent if it’s doing that?


#65

Riserriser,
Sorry for the delayed response.

If you want back illuminated switch panels, you need to bead blast the clear acrylic to get it to look frosted and then paint a layer of white on it top and bottom except for the lamp pockets so the light from the lamps goes into the inside of the acrylic. The reason you want top and bottom painted white is so that the light bounces around inside the acrylic and evenly illuminates the white layer where you are going to have lettering.

You then paint a couple of layers of clear and then a layer of black that you will Laser Engrave so that you have a Black panel with White Lettering. This White Lettering will be illuminated with the Lamps that you put in the pockets.

The Incandescent Lamps get hot and you have to have the Brass .005" Heat Sinks in the bottom of the Lamp pockets (when viewed from the bottom) to prevent the lamp heat from damaging the plastic. This is exactly what the Aerospace industry uses to prevent that. However, in their case, the heat sink is part of a filter that shifts the reddish incandescent light to either pure white or the NVIS Green tint.

Now the trick to the white paint layer (if you are trying to get the same professional results like the Aerospace industry) is that that layer must be even and not so thick to reduce the illumination light level or shift its color. None of the Aerospace manufacturers will tell us what and/or how that white layer is applied to reach those professional results. It is a highly guarded trade secret. You also don’t want the laser to etch through the white layer which is why the two coats of clear between the white and the black layer helps you to avoid that.


#66

Have you considered going with LED lighting? This avoids the heat issue.


#67

Yes, some folks go the LED route. The problem you have is that dimming Incandescent Lamps requires a 0-5V variable Power Supply that can supply high current. For LED’s, you can’t use a variable voltage. You have to use PWM to dim them. That means you don’t want to use a mix of LED Panels and Incandescent Panels in our cockpit. In my case, all of my Panels are Incandescent and I’ve had to make 3-4 Panels myself so I’ve stuck with Incandescent. I’m trying to come up with a design that has Lamp or LED pockets in the back of the panels that can accept either option. However, I have not tested my design.