Hi everyone,

I laser engraved on the back of a mirror by varying the laser diodes power using an US Digital absolute analog shaft encoder timing belted to my Z axis stepper motor. The 0-5V from the encoder is fed into analog modulated laser diode driver to vary the laser's intensity. This process does not require any special laser engraving software, so a rotary engraving image program will work with my process, but I prefer PicEngrave Pro 4 to generate the inverted Lithophane G-code.

The image is not dithered B&W like a normal laser engraving process, but brought into PEP4 as the original after doing some simple editing like gamma adjustment and sharpening. The Z axis depth of cut code slightly rotates the encoder which powers the laser diode up and down based on shading of the image.

The first picture is the back of the mirror after the shade engraving process which looks like a photo negative. When lighted from the back, it looks like the original photo as shown in the second picture. The third picture is showing it viewed from the front without any back lighting.

I have been using this greyscale laser engraving process to create shades for quite some time now on wood.

https://www.youtube.com/watch?v=8xGYtpW00I8

Thanks to forum member Picengraver showing us his laser engraved mirrors in the thread he started, has opened up a new way for me to create art with his software. Thanks John!

Jeff

I did this one yesterday and it's back lit.

Jeff

As always, excellent work Jeff - they have really come out well. 

Tweakie.

Thank you very much Tweakie!

Excellent work, Jeff.

All, it is important to note that Jeff is the inventor and developer of the gray scale image engraving process using an analog controlled (not TTL) laser diode.  He has freely shared his methods with all who have expressed interest.  Larger CO2 lasers do not seem capable of reproducing an image with the same high quality that Jeff is achieving.

For those of you who have an interest, more may be read here: http://hobbycncart.com/forum/63-151-3

John Champlain 

Thank you for your kind words John!

I do have to say, excellent image to g-code creation software to you!!

A little detail of the laser diode I am using, it's a 445nm 1W with a 3 element AR coated focusing lens. I able to focus the beam down to .007" and when I engrave Birch Ply, I use a .008" pixel resolution (stepover) and can run at 50IPM.

I use a 3.33 ratio from the stepper motor to the MA3 shaft encoder and since my Z axis screw being a 2.5MM pitch (.0984") then dividing that by 3.33 gave me .0295" to work with on the 0-5V range on the encoder without changing any steps to the motor. I start out at Z-.0038" for Z zero (just before it starts to burn the wood) This is almost 1V to the modulation input on the laser driver. I set PEP4 to cut at Z-.0255" depth, that gives me 255 .0001" incremental moves (theoretical shades) from white to black. This also gives me a .0002" safety below full depth before the encoder will jump back to 0V. My Z axis only moves half the total g-code travel since it's a 2-1 ratio from the stepper to the screw and does not effect the focus of the beam.

Mirrors are harder to burn so the starting zero point is Z-.0095" more then I used for the Birch Ply, about 2V to the driver. I have PEP4 go Z-.016" more for full power. I can run these at 40IPM with a .007" pixel resolution. I found out that full power to the back of a Dollar Tree mirror it turns white. I'm loosing shades with this setting, but how many shades are there from white to mirror anyway?

Thanks again to John, I am really excited about laser engraving mirrors. I have done several Lithophanes in Corian in the past and never got the detail like I am getting with laser engraving on a mirror. Besides, Lithophanes don't look the same when back lit or not like the mirror does, which is a really cool effect in itself.

Jeff

 

I think all three of you guys are doing some great work. Always follow your threads. Thanks for posting.

Wow! I didn't realise lasering a mirror could yield such beautiful results. And your way to control the laser power is brilliant!

Thanks for sharing.

Dan

Thank you very much, Craig & Dan!

It's been a very gratifying project and adventure.

Jeff

My Laser diode is my brush and PicEngrave Pro 4 is my paint. Tried some white artist canvas using TTL and the texture sure gave it a real nice effect. Sprayed some clear protective finish on it also.