best settings for edge lit sign scan

[Jason Wright]

hi, been registered for ages and not been on here for quite a while now

just bought a few edge lit sign bases to make a few for the kids, may sell some but thats not the priority right now as i use my laser for my automotive trimming business

the machine i have is a 700x500 80w red sail clone, its been working faultlessly for about 3 years now (long may that continue too....)

so i am obviously using cast acrylic and am using the following settings

power 18%
speed 250mm/s
overstriking - unprocessed
scan mode - x swing
interval 0.05


in general the scans are ok, but in certain places the plastic protective film looks to of bubbled up a bit and interferred witht the laser etching so its not consistant or a uniform scan

what i do know is if i take the film off the acrylic i get acrylic vapour marks that are near impossible to remove (or i dont know how)

any ideas how i can get consistant etch scans ?

thank you

[Gene Uselman]

I normally remove the plastic film and replace it with the transfer paper tape [that signshops use]. In the states the plastic film [especially if it comes off easily] is used on cheaper acrylic [extruded] and paper protective is used on more expensive acrylic [cast]. For etching for edgelit, I have found that increasing the focus distance causes the bottom of the etch to melt together and gives a smoother surface. You might experiment with the interval too, that seems pretty close together.

[Jason Wright]

ok thanks, i did wonder if i went too fine on the interval, i just drawn out a test design to try tomorrow with different settings then they can be compared easily

the acrylic im using certainly is cast but isnt the really expensive stuff, im lasering on the all white film side as ive found if i use the film with blue writing on it ill get a blue stain on the lasered /etched part in places, maybe going slower with less power and therefore heat ???

[sebastien laforet]

what i do know is if i take the film off the acrylic i get acrylic vapour marks that are near impossible to remove (or i dont know how)

a solution to that problem is to reduce the air assist to the bare minimum, preventing the air flow to push the vapour back upon your material.

this is also easier if you have a "short" nozzle, with a larger distance between the nozzle bottom and the material. you can get some for very little money on aliexpress (cloudray laser for example is reliable and cheap)

[Jason Wright]

thats a good idea, currently though i just have the supplied air pump so ill need to fit a tap of some sort to control the flow

[Ian Bell]

Hi Jason, been a while...

Minimal air flow - i use a small fish JG type valve 6mm or 1/4"

I remove the plastic film

I use watered down liquid soap, let it dry, then wash off after lasering

I created a test set of squares on a single piece of the target material, from memory I use 15% and 250 speed. For me this gives a nice consistent smooth finish. But of course that's on my machine, although yours is the "same" there will i'm sure be tweaks necessary.

[Mike Tuppen]

line sketch
a. prepare the b&w graphic line drawing (black = etch) use a hi def sketch if possible
b. ensure no odd black bits where they should not be. etching these shows up easily
c. The picture BMP black (etch colour) is shaded to full depth etch (black) on side furthest away from light source and surface mark (light grey) only on closest. This is not so important on 5mm thickness but 4mm and less it helps keep the distant as bright as the close.
d. When greyscal picture complete save it as [name].png
e. use selection tools to select ONLY the outside of the sketch.
f. Increase the selection size using selection modify tool
g. select the sketch area using the invert selection function
h. set the background colour to be black
i. delete the inside of the selection to give a black silhouette slightly bigger than the sketch
j. save file as [name sil].png
k. import both image files into rdw. use the [bitmap handle] to edit the silhouette and the trace option. delete the image leaving the vector. this will be used to cut the outside.
l. place graphic
m. place vector over graphic to match and adjust any traced errors.
n. scale both vector and sketch to required size

photo
i. for grey scale image keep contrast low - do NOT shade top bottom as for line drawing
ii. get silhouette as above
iii. import both bmp and silhouette to rdw
iv. use the [bitmap handle] (old - not rdimage) to edit the silhouette and the trace option. delete the image leaving the vector. this will be used to cut out the outside.
v. place vector over image to fit.
vi. scale vector and bitmap together to required size.
vii. use the [bitmap handle] old to dither dot graphic approx 120 dpi (need to get by trial and error). Also use apply to view to get sufficient dot definition. Adjust contrast and brightness to improve image if necessary.

other settings and stuff.

my settings for 80watt machine

1. add any neck cord holes adjusting the vector around hole
2. adjust any traced errors in the vector. adjust vector base to give required interface size to leds
3. I remove laser side film from perspex then use a mixture of bar soap and glycerine and water brushed onto the surface in as even coat as possible. The mixture should be thick gloop - not runny. after etching the mixture and any deposits can be washed off using toothbrush (soft). Just using glycerine soap bar rubbed on also works but beware grit caught in the bar - any scratches are very visible. I use these soap methods for cutting as well - eases deposit removal.
4. Use a sweep spacing as close to, but less than the beam width, as possible. I use 0.0975mm.
5. power settings 14% min to 28% max line sketch or 18% min 18% max for picture
6. speed 300mm/s
7. I prefer viewside to be smooth. this requires horizontal mirror of graphic AND vector use [transform] in rdw
8. xswing
9. line sketch - output direct (to enable shading) picture (should not be available in picture since it is only 2 colour b&w)
10 run!

badge.png

[Jason Wright]

thanks Mike, thats very consise and for me a cuppa needed to digest all that

this is what ive managed today, still a bit grainy

settings were

18% power
250mm/s
0.13 interval

IMG_6640.JPG

[Mike Tuppen]

possibly 0.13mm is a bit much.
try etching a very thin line at power setting in your example or cutting a line at minimum useable power. Both with the focus, lens and speed you use.
Then view with microscope to determine width of line (cheap usb type is good enough). This is a good starting point. overlapping lines can cause banding as can "under lapping" lines.
Also the vapours will deposit in the base of the etch leaving a thick deposit which I've noticed leaves raised dust tracks removing this may improve matters.

something I've not tried is to defocus the lens and lower the power and then to do a second etch without moving the work, before cutting! perhaps this could "shine" the etch by remelting the dust but not etching further?

Another possibility is to do both an x and y scan (slow) at lower power

[Jason Wright]

plenty more testing to come it seems, this acrylic stuff is not very forgiving