Sample picture needed for Granite/Marble test

[Bruce Dorworth]

I am a newbie. I have an 80 watt Chinese laser. I have it running and have been busy sticking everything I can get my hands on in there.

Well, there was a sample picture that came with the laser, so I engraved it on a piece of plywood. It looked Ok for something on a piece of plywood. So, I tried it on a piece of granite for Home Depot. First was carved to deep, second one was a little lite, third one was not very good either.

I then decided that I needed to start with a known good picture. I have a sample of granite and a sample of marble from laser sketch. These pieces are about 4"x6". If I didn't have to resize the picture that would take one of the variables out of the equation.

One last question, I also would appreciate a recommendation for the laser settings(for an 80 watt laser).

Thanks to all,
Bruce

[Rodne Gold]

Where you need to be careful in terms of your chinese laser and pictures is in the backlash setttings for bidirectional firing , you will never get good resolution unless you tune this setting (same applys to all lasers firing bidirectionally). You need to ensure that alternate lines from either direction line up in respect to start and end point.
You will also most likely need to slow things down to get good precision when using low powers at high high speeds, the glass tubed lasers will have issues firing at the right place with low power at high speeds.
I would start off with around 200-300mm/s speeds and 30-50% power for marble or granite, try bidirectional processing and if that isnt resolute enough , try unidirectional. check what the default stepover distance is and adjust it , stepover is the distance the y axis moves in each scan pass , most of the lasers have a value of 0.1mm , which equates to 250 dpi , you can set this to 0.05mm for a 500dpi resolution , tho on stone , 250 should be more than adequate.
I would also use the "Gold method" of processing pics for the laser (or Photograv) than use the lasers inbuilt greyscale/bitmap driver which are normally rubbish compared to the aforementioned methods.

[Frank Corker]

Bruce,

Sometimes it is the graphic that is not really up to much. Here is a picture which is 300 dpi, this is for wood, give it a try and if the result is good, then your problem lies with how you are processing your image. This for my 45w laser is 45% speed to 100% power.

If your image is obliterated, then your settings are too high and you need to either reduce the power or increase the speed.

If you wanted to try it for granite, just invert the picture and try that on a small area, but remember with granite, you only need a small amount of power to a fast speed - I would do this on my laser at 100% speed and 33% power. You are only going to etch onto the granite, you will not achieve a deep engraving - there is a difference. High speed, low power. Increase the power a little at the time until you achieve your optimum for your machine.

[Bruce Dorworth]

Thanks Frank and Rodne. I will give this a try and report back.

Bruce