While fine tuning the focus of a new lens for my laser diode the other day, I decided to test how fine a spot the lens was focusing too.  This is a dried pinto bean with the maximum height of the letters at .025 inches / .635 mm high.  I think I could have done even smaller engraving if I had reduced the laser power more, but I ran out of play time. 

John

Unreal!    That's just tiny!  Take a picture of a set of calipers set to .025 for a visual.............. that picture is great but doesn't do it justice.  Maybe stretch a hair across the writing long ways?

Brett

Thank Brett,
Good advice.  Here's a couple more pics - best I can do with a makeshift closeup lens.

John

Hey Jeff,
Post your rice grain pic.

John

Like those small pic's.
BTW, smallest letters you can achieve will be based on the thickness of the lines making up the letter or number.
RICH

Hey Jeff,
Post your rice grain pic.

John

Darn, I don't know how I missed this thread and your request John. 

Here it is. I used an old version of Bobcadcam to generate the code and hot melted the grain of rice to a piece of anodized aluminum. Good thing my name is not to long. 

Jeff