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Making Backlit Panels Laser vs CNC Engraving

goldenfab

Aluminum
Joined
May 25, 2016
Location
USA Prescott , Arizona
I have a customer that came to me wanting some avionics back light panels. He is wanting me to machine the front panel out of acrylic or poly carbonate. His idea is to paint and then laser engrave to illuminate text(I don't have a laser setup). This would be prototype and maybe small run production. I know a guy that has a laser but is not interested in taking on work and said its tricky to get the paint to burn off and not damage the plastic. I heard you could sandblast away the paint using a mask but I think this is going to be troublesome with small lettering.

-Am I going to get good results using an engraving bit on my CNC mill (I only have a 4k spindle so its going to be slow going but it should not be too big of an issue for small quantities)?
-Should I recommend acrylic or poly carbonate?
-Any paint suggestions?
-Are there other processes I should consider?
 

Scottl

Diamond
Joined
Nov 3, 2013
Location
Eastern Massachusetts, USA
Burning paint off cleanly with a laser is often a multi-pass deal even on metal. Plastic substrate would be even slower.

I would think a laminated label might be more effective, or silk screening over plastic. There are companies that do both quite well and can make a durable product even in small quantities.

Silk screening in particular lends itself very well to low volume and stencils are easy to photo-reproduce from computer artwork.
 

RyanT

Aluminum
Joined
Jan 1, 2013
Location
Canada
You aren't necessarily concerned about cutting too deep since the laser will leave an attractive frosted finish which could be desirable for backlighting. I'd probably paint/engrave the back for protection.

Some types of paint will turn into gooey burnt gunk instead of vaporizing. Stick to acrylic if its going into a laser.

Raster engraving acrylic is very slow, other options might be better.
 

car2

Stainless
Joined
Sep 19, 2009
Location
Apex, NC
Basically, you will need to leave the lightguide smooth (as in polished) everywhere except where the lettering/text/light-extraction is required. I assume from your post that he wants to light selected areas versus a "uniform" backlight (like on an LCD backlight), and that the lightguide will be edge-lit somewhere (not back-lit).

Depending on the geometry and pattern, the "light extraction" from the smooth lightguide can be done by simply selectively painting the rear surface with just about any opaque white paint where you want the light extracted (what happens is that as the light propagates down the smooth lightguide by internal reflection, when it hits the painted area light passes thru the lightguide into the "matrix" of the paint (which has aprox the same index of refraction of the plastic), and is diffused by the white pigment in the paint. In fact, a lot of uniform edge-lit light-guides are made by printing a graded pattern of white dots on the back side of a piece of acrylic; the dots are less density near the light-source, and become more dense away from the light source). These lightguides are also made by molding in very fine prisms on the back (and front sometimes) of the lightguide. Similarly, you can laser-engrave a selective pattern on the back a side of a piece of smooth acrylic to diffuse the light out. Acrylic has slightly better light-transmission and can be polished better. Also, a white "reflector" (sheet of paper, painted sheet etc) behind the lightguide helps reflect light scattered out the back toward the viewing direction.

Attached is picture of a "project" we're working on, the acrylic tile (magnetically electrically connected) are laser-engraved (random raster density) to extract the light from the edge LED's.

Feel free to drop me a PM if you have any questions or want to send a sketch for $.02 advice (and warranty of the same amount). Cheers Charles

tiles1.JPG
PS if he wants uniform backlight panels, you can buy edge-lit LED ones that are used for display signs (like the transparent backlit prints seen in airports, vending machines etc, these replace the bulky box-fluorescent ones), and there are edge-lit lighting fixtures. Also, you can tear apart any old device with a backlit LCD to see what's going on, they will all have edge-lit uniform backlight panels with various diffusor layers (some TV's use direct back-lighting, with LED's and diffusors, versus edge-lit panels).
 

car2

Stainless
Joined
Sep 19, 2009
Location
Apex, NC
Here you go: Done..

Inventables: 2 color reverse engravable Acrylic

I'm sure just about any sign shop could make the parts you want.

If *edgelit*, that material, due to the coating, will basically absorb all the light in a short distance as it travels down the material. If just an opening in a transparent material is needed, any painted acrylic, pc or other clear plastic can be used, or cut vinyl (which would leave the smooth surface undisturbed), and yes about any sigh shop, or someone with a laser engraver can do it. An edge-lit light guide with any complexity/size is a different problem.
 

John Welden

Diamond
Joined
Mar 21, 2009
Location
Seattle
If *edgelit*, that material, due to the coating, will basically absorb all the light in a short distance as it travels down the material. If just an opening in a transparent material is needed, any painted acrylic, pc or other clear plastic can be used, or cut vinyl (which would leave the smooth surface undisturbed), and yes about any sigh shop, or someone with a laser engraver can do it. An edge-lit light guide with any complexity/size is a different problem.

The op asked for backlit.
 

Mooner

Aluminum
Joined
Apr 14, 2016
If laser engraving, use Acrylic only... Polycarbonate does not cut cleanly with a CO2 laser (burns / melts / smells nasty) and can release benzene (carcinogenic) or cyanide (poisonous) gasses.
 

MJR7

Plastic
Joined
Jul 8, 2006
Location
Louisiana
i once made an overlay for an updated instrument panel using polycarbonate. i believe it was .187" or .250" thick but memory fails. aircraft was an antique grumman amphib that we completely restored. some instruments, mainly engine ones, had no internal lighting and we didn't want to clutter up the look of our modern panel with stand off lighting. the overlay of course, matched the panel layout and i cut chamfers on the backsides of certain instrument holes so as to allow light to pass thru to those instruments needing illumination. lexan presented no issues with paint. i used white deltron and painted both sides of the panel, two coats on the rear side and several on the front side. i then painted the rear side black and the front side a color the customer requested. we used aircraft style cylindrical lights that passed thru the overlay and screwed into sockets placed where needed to both fasten the overlay to the instrument panel and also allow light to travel within the overlay. of course, the backside of the overlay instrument hole chamfers and fastening holes in the overlay were left unpainted. the lights had caps or heads on them with rubber seals and were made in such a way as to allow finger tightening. all of the placarding was done by a very skilled local engraver using the standard mechanical engraving equipment of the day. engraving depth was thru the topcoat into the white deltron making sure to not reach the clear lexan. when the panel was lighted, the placarding was easily viewed since it was all lit up from the light traveling within the lexan and the instruments needing illumination looked like they were internally lit. this amphib had extensive breaker panels, throttles, mixture controls, flap controls, etc. all forward and rearward overhead in the cockpit. all of these panels were made the same way and all labeling/placarding was internally illuminated thru the overlays.
 

MaxPrairie

Hot Rolled
Joined
Jul 9, 2015
Find someone with a laser willing to do it and raster the lettering on. Acrylic cuts really nice in the laser.
 

car2

Stainless
Joined
Sep 19, 2009
Location
Apex, NC
If all that is required is backlighting through the panel (not edge-lighting), and depending on the shape of the panel, there are many options as everyone mentioned above:
a)Painting lexan or acrylic with an opaque primer (krylon rattle-can gray, black will work fine, couple of light coats), the paint may be mechanically engraved off, or laser-engraved off (picture attached of a part I happened to be working on, that's krylon yellow paint on lexan laser-engraved off (2" dia disk, .006 wide lines) (the paint is not completely opaque in this example (opacity wasn't needed). The pre-coated materials JW mentioned would be similar.
b)mask (could be a laser-cut mask or cut by a sigh shop, stencil-cutter, or exacto knife) the clear part where light transmission is wanted and paint the background (no machining or engraving required)
b)stick on a adhseive vinyl pattern cut at any sign shop or with a stencil-cutter
c)print out a black artwork and stick adhere it to the part (if something ultra-precise was wanted, you can get an emulsion artwork (, black emulsion on mylar sheet used for printing and PCB's)

To your original question of CNC versus laser engraving, laser engraving just requires any artwork (no cnc programming), and can produce halftones and precise features, and does not require any fixturing or stress on the part--provided the part is relatively flat without a bunch of raised features that would obstruct the laser.
Alghough lexan will not cut well at much thickness with the common CO2 laser-engravers, it's OK for thin sheet and engraving off a paint layer. Clean the surface with mineral-spirits or alcohol after engraving. Cheers

IMG_5620.jpgIMG_5623.jpg
 

surplusjohn

Diamond
Joined
Apr 11, 2002
Location
Syracuse, NY USA
I have done this with silk screen ing. Easy. Lexan 8020 is a graphic arts film intended for this. Membrane switches are made this way. Plexi works too. Cut film works also and offers some effects not available with silkscreen. Resolution is greater than you may guess but not as fine as silkscreen. I know this is done with ink jet also requires a 6 color head so to dispense a pigmented white blocking layer. I question the sharpness.
 

OnePerfectTool

Plastic
Joined
Apr 7, 2012
Location
Riverside
I have a customer that came to me wanting some avionics back light panels. He is wanting me to machine the front panel out of acrylic or poly carbonate. His idea is to paint and then laser engrave to illuminate text(I don't have a laser setup). This would be prototype and maybe small run production. I know a guy that has a laser but is not interested in taking on work and said its tricky to get the paint to burn off and not damage the plastic. I heard you could sandblast away the paint using a mask but I think this is going to be troublesome with small lettering.

-Am I going to get good results using an engraving bit on my CNC mill (I only have a 4k spindle so its going to be slow going but it should not be too big of an issue for small quantities)?
-Should I recommend acrylic or poly carbonate?
-Any paint suggestions?
-Are there other processes I should consider?

You are welcome to call me. Our company specializes in Bomb Mask manufacturing, as such laser engraving will be no problem.

We do Boeing/Northrop/Government sized jobs and we do Mom/Pop sized jobs... Do not worry about limited production-every customer gets spoiled at our factories.

Stephen G. Elder
Chief Operations Officer
Precision Innovation, LLC
Black Ops
(951) 515-6029
 

goldenfab

Aluminum
Joined
May 25, 2016
Location
USA Prescott , Arizona
I'm in Dewey, its outside of Prescott. My customer has yet to get me a final design to quote. If its not something I can do in house I'm thinking it may be better for him to go with a one stop shop for this need.

Thanks everyone for the feedback.
 

goldenfab

Aluminum
Joined
May 25, 2016
Location
USA Prescott , Arizona
After a lot of persistence from my customer wanting me to make this happen I figured out a way. The first prototype I painted poly-carbonate with automotive paint and CNC engraved lettering through the paint with a .01" end mill. The results were quite good actually and the back lighting was excellent but there was not enough definition without back lighting.

I found a guy with a laser that was willing to work with me and we figured out a process. Took a fair amount of experimenting with different paint layups and laser settings. I used cast acrylic sheet, several coats of white paint and just enough black paint to cover the white. The black paint was lasered off to reveal the white and presto, the back lighting is even working. I did a clear coat after the laser work. My customer was very happy with the results, I have a second order I am working on now and am expecting more in the future.
 

Monarchist

Banned
Joined
Oct 2, 2012
Location
Sol, Terra
I have a customer that came to me wanting some avionics back light panels. He is wanting me to machine the front panel out of acrylic or poly carbonate. His idea is to paint and then laser engrave to illuminate text(I don't have a laser setup). This would be prototype and maybe small run production. I know a guy that has a laser but is not interested in taking on work and said its tricky to get the paint to burn off and not damage the plastic. I heard you could sandblast away the paint using a mask but I think this is going to be troublesome with small lettering.

-Am I going to get good results using an engraving bit on my CNC mill (I only have a 4k spindle so its going to be slow going but it should not be too big of an issue for small quantities)?
-Should I recommend acrylic or poly carbonate?
-Any paint suggestions?
-Are there other processes I should consider?

Done "many such" for prototype 'tronics.

Easy-peasy is to do the art, "however", on clear Mylar then contact print a 1:1 scale negative (or "positive") with ordinary photographic film.

Mount that behind your acrylic or Polycarb, add a layer (or several) of coloured film(s) back of the clear legends, light it up, and DONE.

Only "machining" is to drill holes cleanly for switches & c.

See "paper drill" - easily DIY'ed for uber-clean cuts in thin materials.
 

goldenfab

Aluminum
Joined
May 25, 2016
Location
USA Prescott , Arizona
I thought I would update with my success after a long time coming. I ended up machining acrylic to shape. I shot the panels with a white then black automotive base coat paint. Another member on here Brian (Lamb Tool Works) lasered off the black for the text. I then shot it with an automotive clear coat. After a lot of trial and error we got the process dialed in.

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