Laser Engraving True 8bit Shades of Grey

[Scott Shepherd]

How much would a 39" X 24" CO2 laser cost?

Jeff, what does that have to do with it? Are you asking how much a 24" x 39" laser costs because cost has some role in this? If cost plays a role in this, then that proves the point so many are raising. 3 hours to do a 9" x 7" piece isn't cost effective. So if cost (of the laser) is a concern to you, then why isn't cost of engraving a concern to you. I might spend $40,000 for a machine that large with the high definition optics on it. However, I'll make the difference up in speed when compared to the savings you'll get with the laser.

If time doesn't matter, then why does cost of the machine matter? The two are linked together, not separate. I've asked at for a photo we can engrave to compare, but I've seen nothing yet, but photos of your finished product. If you want to compare things with people, post a link to a file we can use to create something to compare to.

[Jeff Woodcock]

Scott, I was just curious what the cost would be for that much travel on a CO2 because you posted a picture of a router like my servo and was talking about my building costs. I have already posted a picture link in post #53.

Mike or Rodne can you please remove post #77. It's just another personal attack.

Thanks. Jeff

[Scott Shepherd]

Thanks Jeff, I missed that link to the photo. I've downloaded it and I'll give it a try when I get a chance.

[paul mott]

In between the engraving jobs I had a chance to try Jeff’s picture image which he posted earlier. It’s only a scrap piece of wood and the result is a bit on the dark side but it does, I think, illustrate that CO2 lasers can reproduce 8 bit shades of grey without any dot-dithering.

This is only 120mm x 90mm and with a feed-rate of 4500mm/min and 0.2mm step-over took approx 12 minutes to complete.

Paul.

DSC01502a.jpg

[John Champlain]

Nice, I just may have to get a glass tube after all for my new machine like you mentioned before.
John

[paul mott]

Naa, your new diode will arrive in the post tomorrow.

Paul.

[Jeff Woodcock]

Paul,

That came out excellent. You sure blew me out of the water with that one.

Can't wait to see Scott's engraving.

Jeff

[paul mott]

Perhaps the most remarkable thing Jeff has presented in this thread is that diode lasers can be used to reverse engrave ‘shades of grey’ into mirrors.
It may not be immediately obvious but whilst the mirror’s reflective substrate is essentially a 1 bit material (either present or not) the mirror’s backing paint is not a 1 bit material - therefore the final effect of ‘shades’ can be produced in a similar manner to that produced on wood, canvas, etc.
I have not actually tried it, but I suspect this process cannot be achieved with a CO2 laser because of the 10.6um wavelength. However, for the enquiring mind, it is certainly food for thought.

Paul.

[Rodne Gold]

Paul , as far as I know , The paint backing is merely a protection of the silvered side , unless the silvered side is actually not 100% reflective , messing with the paint layer will do nothing. In all probability the "greyscale" is achieved by the increase in power changing the size of the vaporised or burned spot due to collateral heat damage...

[paul mott]

Hi Rodney,

You may be right, as I said I have not actually tried the process, but if you take a close look at Jeff's mirror the 'shades' are there. IMO the process not only messes with the protective paint layer's, it also messes with the reflective substrate.

Perhaps Jeff could explain how this happens ?, please.

Paul.

[Rodne Gold]

What we need to see is a macro shot of portion of the engraving so one can see what's actually going on , I have a 10x and 20x loupe and inspect engraving with that , it's an invaluable tool as you can diagnose and see EXACTLY what the laser is doing with respect to the material.

[Jeff Woodcock]

Paul,

when I'm engraving mirrors I have to use the Lithophane setting which reverses the power levels. At full power, which is full Z-.0256" depth of cut in the gcode turns the coating white when viewing it from the front. I have to start out at power level 95 (Z-.0095") for silver. That is the power level just before the reflective coating starts to change and from there is 160 power levels to the white at full power. I can only estimate what I'm seeing and it's maybe only 20-30 shade differences when engraving mirrors, but like you said, there are definitely shade changes.

I used TTL on the very first mirror I experimented with and really did not think varying the power would work very good. The first picture I attached is the very first mirror I engraved by dithering the image B&W and pulsed my laser diode on a cheap Dollar Tree mirror. My wife asked me to engrave an angel for her. The second picture is the Spirit mirror engraving using analog modulation on a DT mirror that I posted before in this thread when viewed from the back. It looks sorta like a photo negative.

Paul, I don't know if this answers your question or not. If not, I don't really know how to explain what is happening with the either of the two coatings. I just know what I see is a smooth transition from white to the reflective coating to give what shade changes there are.

Your CO2 has more power to be able to implement more of the shade levels on a mirror then my laser diode, so why not give it a try? I did not expect the results I got at first either, but you may be able to get a few more shade changes then I did.

The last picture is an example of how small I can engrave text with my LD engraving machine.

Rodne, I can zoom in on an area and post a picture later to see up close what is going on if you want me to. As you know there is a size limit of pictures you can post here, but I could try to get it close to the max.

[paul mott]

Jeff,

As said previously I doubt that the process is even possible with a CO2 laser because the 10.6um wavelength will also attack the rear surface of the glass causing micro-fractures which will probably appear white in colour and perhaps spoil the overall result.

Thank you for the explanation but as you say I will really have to try it for myself to see just what happens.

Paul.

[Jeff Woodcock]

As you can tell, I don't fully understand how the CO2 laser and your setup works because I have never used one. Most here that use a CO2 probably has a hard time understanding how the laser diode process works too for the same reason. I know you started out experimenting with the LD, so you have some experience with them.

[Dave Gabry]

CO2 lasers work on mirrors too. I'm still very new to this new toy, and need more practice to get it right. Photo is of a back-lit mirror tile. Original photo was half-tone dithered then sent to the laser.
Dave

mirror sample.jpg