Granite engraving problems

[colin smith]

Hi all, I am new to this forum. I am using a 40watt laser engraver and using photograv. Whenever I try to engrave granite no matter what speed settings i use or power setting the engraved image never comes out like the simulated one. there is always to much black. when i try and compensate then the white burns to deeply. Is there something obvious that I must be doing wrong

cheers

[Rodne Gold]

Try this , rather than let photograv invert the pic (PG will invert it if you laser on black granite) , Invert it in Corel or photoshop 1st and then run it in photograv using the cherry wood settings without using Pgrv to do the inversion.
If this doesnt help , then try lightening the picture before doing the photograv processing , the lighter the picture - the more white you will have when its engraved (when doing granite or black stuff , white engraves and black doesnt)

[colin smith]

many thanks for that. I will let you know how it works out

cheers

[Larry Bratton]

I have not tested this, so take it for what it's worth..Laserbits has developed a new granite parameter for Photograv 3.0. I downloaded it, but it can be downloaded free at
http://www.laserbits.com/images/Lase...meters2010.pdf

[colin smith]

thanks for the help. i tried the method of inverting in coreldraw. not really any better. Iam starting to think that maybe i have greater expectations as to the results that should be gained. is there a size of image that engraves better than others. eg 5 inchs, 10

regards

[Larry Bratton]

Colin:
A little more info please. What is the original quality of the photos your trying to do? You need to start with something in the 200 to 300 dpi range. Photograv likes 300. Are you doing any work on the photo prior to submitting to Photograv? i.e. sharpening, changing contrast etc. I also convert mine to greyscale in Photoshop if their color, but that's a last step. Photograv will convert it if you forget though.

[Chris DeGerolamo]

Size of the image should not matter; resolution may be an issue though. Maybe you should post the image if you feel comfortable. What settings are you using? Machine? A little more information would help to troubleshoot...

[Lee DeRaud]

One thing: granite is extremely easy to over-power. Try a small test (at this point it sounds like you should have plenty of scrap material) using settings that are much lower power than 'standard'. By "much lower" I'm not talking 10%-20%: divide by two, and if that doesn't work, go down another factor of two. (The idea is to work your way up from not-enough rather than work down from too-much.)

I'd also suggest dialing in your settings using whatever halftone/grayscale options your machine's drivers provide before complicating things with PG.

[colin smith]

the resolution of the picture is 300, Iam quite good with photoshop and i have spent hours and hours editing. removing the background, altering the contrast, brightness, using the lasso tool to work on different areas of the picture.
on the power settings i have started off real low power, so not to overburn. Iam not sure which picture to post as I now have tons all of the same image edited in different ways.
Does anyone have a photo they have done, so i can see what kind of results can be achieved. I now have gone through 10 slabs of granite(black)

[Chris DeGerolamo]

This is a really stupid question but I'll ask anyway: Are you focused to the material properly? And you are sure the laser is firing? Have to ask...sorry.

Here is a low res image of what we have done. These are 6x6 FYI.

[Frank Corker]

If the image looks half decent and you are engraving a reverse image - try 100 speed and 33 speed should get you a good result.

[Dee Gallo]

If the image looks half decent and you are engraving a reverse image - try 100 speed and 33 speed should get you a good result.

Or is that 100 power and 33 power? Not too often we get to call Frank on something!

[Dan Hintz]

Frank's suggestion should be (I believe) 100S/33P.

Do small 4x4 images on various spots of the tile... you'll go through a lot less tile that way until you get the settings correct (learned that one the first few days of the scrap pile getting higher and higher).

[colin smith]

Yes the laser is lined up properly and is the correct distance away from the work.
i will be honest i have not tried it as slow as 100, the min i tried was 200, but i kept reading to try engraving faster.
what scan gap are you using at 100 speed

regards

[Dan Hintz]

Ah, we have a disconnect here. Most of us own Epilogs, ULS, or Trotec machines, so when we say 100S, that means 100%... for Epilog/ULS machines, that's around 75ips, for some of the higher Trotecs that's as fast as 140ips. You'll need to convert these figures into something appropriate to your machine.

On granite, you should be engraving in the 150-300dpi range... anything higher and you could be blowing away your detail.