Laser Engraving True 8bit Shades of Grey

[Jeff Woodcock]

Dan,

I do understand what your saying, but our experimenting is evolving and improving as time goes on. What we are doing is allot closer to linear laser control then dithering an image and pulsing the laser. I do have to change power levels and settings based on the different substrates. You all must know pictures presented on any forum does not do them justice as seeing them in person. I do see them totally different then you do. Your correct about mirrors. How many shades are there from white to silver? One difference I see is, there are no dithered dots when lasering these with variable 256 power levels. There are smooth transitions from what little of the shade changes there are, but I do have to disagree that there are no shade differences. I'm not here to argue with anyone, just to present what our outcome of this experimenting has produced.

I'm not doing this for any business purpose either and if you read my posts, it was no way presented in that manner. I own a CNC machine shop and this laser engraving is only a Hobby for us and just wanted to see if others were interested in this process also.

Mike,

I did read the rules and asked the question about posting the PDF and explained what it contained, but did not really get an answer. I thought by Rodne's comment, there was an interest and he is a moderator so I posted it. I do apologize if it does not follow the rules. I understand all this I presented is somewhat backwards to most here with the expensive CO2 machines used by everyone and is not a practical business idea to be considered. I ran across this web site and seen one of my Artist Canvas laser engravings that was posted in another thread and decided to join.

[Vicki Rivrud]

I've had a look at the pics Jeff Posted, whilst they do look good, they do show a distinctive banding pattern much like an injet printer does. My images engraved using the Rastus filter the more traditional way on the laser don't show the banding.

Hi Steven,
What is a Rastus filter??
Vicki

You were probably rolling your eyes with this question! Well after a search here, I found the 3/2012 post and over the net more info - its a Photshop filter - I don't do Photoshop and the Corel plugin is for Corel Painter - don't do that - -after 6 years of learning all kinds of software and getting to know my chinese laser and its software - -etc etc - - Still have lots to learn . . . seems I continue to learn something new each day. Learning CAD & Corel & Photograv was a big achievement too - sometimes a person can just get overwhelmed with needing this and that . . but so it goes

[Mike Null]

Jeff

Glad to have you on board. We have a number of members who are interested in the technical side of things and your topic is definitely interesting to them and to us on the fringe. I can imagine even more folks on the cnc forum are keeping an eye on this as well.

I think we all recognize that your intent is to inform and share.

[Rodne Gold]

I really dont think your pdf is in any way contravening forum guidelines in terms of a commercial interest
According to what I read , you use a Z axis encoder to vary power levels , how do you derive the Z axis info -- I don't know Mach3 - so is it some sort of transform mach 3 does to convert greyscale bitmaps to variable Z axis height to do a 3d type carving?
I also note you DO say this wont work for higher powered CO2's
What is the lifespan of such a diode , what does it cost with heatsink et al?
I wonder if such a device could be used to ablate a resist for electro or chemical etching of metals?
What other substrates does this work on? anyone tried clear acrylic?

Anyway , its great that you share this with us , it definitely does have some overlap and relevance to what we do here..

[john banks]

My 100W RECI glass tube has too low a slew rate of its output power to make grayscale engraving commercially attractive. At 1000ipm it is feasible, but I have to run about 100ipm to make grayscale stuff look sharp. Even then, the greatest contrast in wood is between 0 and 8% using TTL switching, rather than between 8% and 90% using PWM output control.

I think titanium could be awesome with the described method from the point of view of the power output, the wavelength and the colors. I've seen a 1W galvo in the UV, visible and near infrared regions make a very sharp and fast image on titanium, but it wouldn't be a good CNC conversion project due to the slow speeds.

It is getting that right combination between controller, power, wavelength, material and speed. There are probably some value propositions using cheaper parts such as a diode and galvo that on the right material could be great?

[john banks]

How about using three channels of audio output from a computer... two channels to control a cheap set of galvos and a third channel to control the power of the diode? Should be much faster if the diode has enough power to mark the material quickly enough.

[Jeff Woodcock]

I really dont think your pdf is in any way contravening forum guidelines in terms of a commercial interest
According to what I read , you use a Z axis encoder to vary power levels , how do you derive the Z axis info -- I don't know Mach3 - so is it some sort of transform mach 3 does to convert greyscale bitmaps to variable Z axis height to do a 3d type carving?
I also note you DO say this wont work for higher powered CO2's
What is the lifespan of such a diode , what does it cost with heatsink et al?
I wonder if such a device could be used to ablate a resist for electro or chemical etching of metals?
What other substrates does this work on? anyone tried clear acrylic?

Anyway , its great that you share this with us , it definitely does have some overlap and relevance to what we do here..

Hi Rodne,

Sorry for such a delay in responding. To answer your question about the Z axis control. First Mach3 is an open source CNC controller program for CNC lathes, mills, routers, lasers, plasma torches, basically any machine tool you want to automate with up to 6 axis control and it runs gcode files. It even has a plugin for engraving photos using a CO2 laser. Mach3 is a Windows based program. http://www.machsupport.com/


I have been making Lithophanes with my rotary spindle in Corian on my servo router with X,Y and Z axis gcode files. Any image to gcode program generates the Z axis moves based on 8bit shaded values of the image. I thought why not try getting the Z axis gcode commands to control a laser in the same manner to burn 8bit shades. I wanted something that the Z axis motor could rotate to vary the power and ended up with the analog shaft encoder, an analog modulated driver and a 445nm laser diode. This was not my first setup or attempt, but like any experimentation over time it improved and progressed to what I am using now.

I have over 800 hours on my laser diode setup already with no failures. From what I have read, the laser diode I am using is from a laser projector, so they have a lifespan in the thousands of hours providing they are not over driven with amps and have a good heatsink. Cost is shown in the PDF and links to components.

I have built another, more powerful laser where I used two 2.5W 445nm laser diodes slightly angled in the heatsink housing to focus at the same intersecting point. My K2CNC servo router will not run a fast enough blended feedrate to handle the power of this laser, so I'm in process of modifications to that machine. I will be using an encoder again, but tied to a 4th axis servo motor because I can't have the Z axis moving and effecting the intersecting focal point. When bench testing, this laser will actually cut wood and heat resistant automotive gasket material.

At this time, I feel the reason my process will not work with a CO2 to engrave 8bit shaded images has really been explained by you already. You said there are CO2 lasers that does have 256 power levels, but there only for 3D engraving. Imagine the speed it would need to run so they are not cutting into the wood and only creating a 2D shaded engraving. This is what I am trying to overcome on my new build now (lack of speed)

I hope I have some of you thinking about this and maybe someone will come up with a way to do it with a CO2.

[Rich Harman]

I think the best way to do it with a CO₂ is to defocus, set the scan gap to a large value and make a very large image. It would look terrible up close but from a distance it may look quite nice.

[Jeff Woodcock]

I think the best way to do it with a CO₂ is to defocus, set the scan gap to a large value and make a very large image. It would look terrible up close but from a distance it may look quite nice.

Here is another members attempt he made after seeing what I have done on another forum, but it was just overlapping the dots. Very good results, but he was still pulsing the CO2.

http://www.sawmillcreek.org/showthre...Shades-of-Grey

[john banks]

When I used variable power by grayscale on my CO2 laser it did vary the depth and the shading, but it didn't look as good as dithering (as well as being a lot slower) due to low contrast.

I'm struggling to understand what is being proposed here that is different to existing 3d engraving (that hardly anyone uses on CO2 lasers though) as the power is still being modulated by grayscale information, there is still a heat affected zone and all that goes with that. It appears that running slower with a diode of a different wavelength and lower power gives better shading.

[Michael Hunter]

I'm struggling to understand what is being proposed here that is different to existing 3d engraving ....

I suspect that the difference on wood is that Jeff's low power/low speed method gives different levels of scorching but with little or no removal of material ("depth").
More akin to pyrography than standard laser engraving.

Difficult to achieve this effect with a glass tube laser, since they don't like running at very low power and almost impossible with an RF laser because of the way that they control the power output.

[john banks]

Much more subtle with the low power then.

Can you explain about the RF method of power control - not owning one I assumed you could use a powerful RF tube and ramp up and down the power very quickly indeed with precise control?

[Rodne Gold]

RF tubes do vary the power levels according to greyscale , my GCC's with synrads and coherent Deos tubes do this.

[Michael Hunter]

Dan might correct me on this, but ....

My understanding is that RF tubes always deliver full power when they fire.
Average power (applied to the material) is altered by varying the length of time that the tube is "on" for each dot fired - PWM or Pulse Width Modulation.

When rastering, my (ageing) Epilog only fires on the "grid", set by the DPI setting in the driver.
Possibly the newer ones (with "3D" capability) are capable of firing apparently continuously, but the power level will still be set by PWM.

[Rodne Gold]

It doesn't matter which way max power is varied , it still varies at the substrate whilst the head is travelling at a constant rate according to greyscale ..aka 3d engraving...which is what we are talking about..