Rabbit Laser photo engrave help.

[mark pirtle]

We bought a rabbit laser about a yr ago and never got a quality picture to engrave on anything other than poster board. We got frustrated with it and basically stopped messing with it. Here is what I need. I need a file that someone got to work well and what material they used and the speed and power. We have a lot of money in software.

We have the following software.
Lasercut 5.1
Corel Draw x4
photoshop CS4
Abobe master suite
Auto-CAD 2010

We are talking $3000 in software and $7000 in a machine that will only cut and not engrave anything. This is really getting to me and my GF has all but gave up. Can someone PLEASE help us out. We have a RL-60-6090 with a 55mm lens.

[Larry Bratton]

Mark:
I'm not a Chinese laser guy, but we have some people here that are. In the meantime, why don't you post some of the output failures you have had, along with as much information as you can about your settings etc. That will go a long way in helping you solve your problem, if it can be.

[Frank Corker]

Mark, no doubt that you are getting frustrated, this is bound to happen when you first start out doing photos and you need to be persistant but patient with your efforts.

Look inside the zip file attached, there are three small picture files to try, all are 300dpi - use the binary.bmp and the Image300 Wood (eng).tif for wood samples and any material with a light background. There is also a clear acrylic.bmp which you can use for acrylic.

Speed and power settings - start with 100% speed and your power about 45 - run a couple of test areas and alter the power up or down depending on how dark the image result is. If it's black, too much power, if you can't see it, then it is too little. Post your results and then we will see if we can't help you get what you are trying to achieve. The image files attached have been run through photograv and should be ideal for engraving purposes.

[Bambi Bell]

Hi this is Mark's girlfriend Bambi, Thank you for your responses ...The main problem that we have is that when anything calls for 100% power on our machine that would be 1000 through the Laser cut program? is that correct? That seems to be awfully fast, I have usually been taking it down to about 250 to 450 to keep some detail in the photo and adjusting the power to get the definition and contrast...If I take it to 100 through that program I have to set the power way down to 15 or it will burn through but much lower and it won't fire at all...I'm so lost:confused:
We were experimenting last night and I tried anywhere from 900 power to 100 the best results I've had in the past have been around 250 or 200 for photographs. Now our Machine's actual settings on the board show 100% for both speed and power and we have been just setting these through the program not the machine itself. I'm wondering if we need to adjust the machine itself to something different? Our photograv software suggests 800 dpi and I have it set up that way in that program, does anyone know if that is correct also? I'm so frustrated and Mark is frustrated with me, I'm an artist and he's an engineer enough said;) We don't speak the same language most of the time...
I will play with it some more tonight and post some examples, thank you so much for any help it is so appreciated!!! :D

[Larry Bratton]

Bambi:
Never use the recommended settings from Photograv. As Frank advises though, your going to have to experiment to get your optimum settings for each type of material. I am not familiar with your laser software's settings as they would relate to Epilog settings as both myself and Frank would use. James Jaragosky member here is our resident Chinese laser guy, maybe he will respond, or if you send him a PM he will respond. I believe he has a Rabbit.

Also, have you checked your laser's alignment, optics and all that normal stuff? The machine will never give satisfactory results on cutting or engraving if it is not aligned.

[Dan Hintz]

Mark/Bambi,

PG does an acceptable job of creating a dithered image, but it wouldn't know a proper setting if it was standing right in front of it. Though it can help in some circumstances, none of that fancy, expensive software is necessary to get good results out of the machine.

Be aware of your substrate and the difference between dpi and ppi... low-resolution substrates like wood, paper, etc. are usually engraved at low dpis (250-400 dpi) to start. Going higher leads to slower times, but it can also make for a darker burn (which is useful at times, but that can also often be accomplished simply with more power). Lowering the ppi for vectoring on flammable substrates like wood help cut down on charring... 500 ppi is a good max point, 250 ppi a good min point.

For rastering images, start at 100% speed and dial up the power until you get an acceptable mark. For vectoring, find the maximum speed your machine can handle (never 100%) and still produce a smooth cut line, then increase your power until you completely and consistently cut through (air assist may be necessary). You may need to decrease speed even more if you have a lower power machine.

Experimentation is the key.

Oh, and do not modify the image output from PG in any way other than cropping. Scaling, filtering, etc. are sure-fire ways to destroy your image.

[Linda Smith Alabama]

The main problem that we have is that when anything calls for 100% power on our machine that would be 1000 through the Laser cut program? is that correct? That seems to be awfully fast, I have usually been taking it down to about 250 to 450 to keep some detail in the photo and adjusting the power to get the definition and contrast

Did you mean 100% speed is 1000? On our 9060 (similar machine but ours is not made by Rabbit) the max speed is 400 and max power is 100. We also use LaserCut and CorelDraw. We get good results engraving acrylic at 400 speed (100% speed) and 15 power. We just replaced our tube; before replacing it we were engraving black granite at 150 speed 16 power. I'm attaching a sample photo of black granite done in 300dpi/150 speed/16 power (you could probably run it faster because we were compensating for a dying tube.) If you'd like to try running this file let me know and I'll send it to you.

One thing I learned is to make sure your scan gap matches your dpi. We mostly stick with 300 dpi. The scan gap for 300 dpi is .084mm. There is a chart somewhere to show the scan gap for different dpi settings, but I can't seem to find it right now. :p

[Linda Smith Alabama]

Aha, found it! :D

DPI = Scangap
1200 = 0.02116
800 = 0.03175
600 = 0.04233
500 = 0.05080
400 = 0.06350
300 = 0.0846
200 = 0.12700
150 = 0.1693
100 = 0.2540

25.4/DPI wanted = Scangap

[Larry Bratton]

Nice job there Linda..maybe we should consider you as resident expert :)

[Larry Bratton]

Here is some info on scangap that may be helpful. I copied this from a post in another forum posted by a person from Romania, but it sounds good. I guess some of you engineers can correct it, if not.

The scan gap is the distance the laser moves vertically (the Y axis) between passes. I think the Rabbit laser software expresses the distance as a fraction of a millimeter, ie. 0.1 is 1/10 mm etc. Because I am used to resolution expressed as standard numbers DPI (dots per inch), I converted mine and keep a chart near my computer. For example 300dpi is 300/25.4 dp mm which equals 11.811 dpmm. To convert it to distance between dots (passes) in mm you invert the number. So 1/11.811 = a scan gap of 0.084mm. I did this conversion for all the common usable resolutions which are 600, 500, 300, 250, 200, 150, 100, 75, 50, 40. Easier for me to remember than .084. When engraving photos, you want to use a scan frequency that is a multiple of the dot screen applied to the photo to convert it to a 2 bit .bmp file. This avoids a moire which is interference which is resultant when two lined patterns are superimposed and are out of phase. Like placing two pieces of screen material together at a slight angle.

If that seems simple, hold on to your hat. There is another variable affected by Scan Gap, power. It's actually logical. The laser spot on any material is not a crisp circle. The burn microscopically varies from material to material. It's similar to the pattern of a flashlight on the wall with an intense centre fading out to the edges. When engraving an image made of dots, the resolution is maintained by definition between the "black" zones and the unburned "white" zones. Some marerials .are inverted.

Each material is different. When the scan gap is close, the edges overlap which doubles the power at that point on the material. As the centre spots get closer, as you can imagine, the effect can be quite a dramatic increase in power. This sound efficient but in reality negatively impacts the image resolution, tending to blur it. So dependng on the burn rate of the material, you may have to increase the scan gap to get the optimum resolution. Wood for example requires a much wider scan gap than anodized aluminum.

Some brittle materials like glass, granite and marble don't burn but tend to microscopically fracture from the heat of the laser. (I think marble and granite fracture, open to correction). Anyway, if the scan gap is too close and the laser overlaps too much, the glass heats up and fractures through the area between dots resulting in a blurred, low res image. Some acrylic too tends to melt the whole surface when the dots are dense in the shadow areas and you loose resolution completely in the shadows resulting in a throw away.

These are just a few things I have learned by myself with trial and error and reading some scientific stuff on lasers and how they interact with materials. From this one realizes that laser focus and optics can make a huge difference. I have been thinking of getting an optically better (more expensive) lens for my laser to see if this in fact makes a difference to the resultant dot pattern. By the way, I experiment on plain, cheap brown card for the basic settings. It engraves quickly and holds a photographic image quite well.

[mark pirtle]

Thanks to everyone. I was resizing after PhotoGrave and well I didn't do that before and now we are getting some of the best results we have gotten since we got it. I just did a scrap mirror and it also turned out great.

[Larry Bratton]

Mark, as you go along with this, you will learn that Photograv is more of a convenience than it is a necessity. You have all the software tools to get as good or maybe even better results without it. I also own it, but I have, after messing with it for 3 years, gone to using my other software for dithering. Corel Photopaint has dithering patterns built in when converting to 1 bit images. Photo was edited, dithered and engraved without the help of Photograv. (This is on black granite)

[Ernie DeMartino]

Thanks Larry & Linda,
I've been searching for info on scan gap for months; appreciate it.