Just added this free tiny stroke only alphabet to the showroom here: http://www.ponoko.com/design-your-own/products/tiny-stroke-only-alphabet-5557 and wanted to add a post here about it as well with some larger images.
The free file contains the entire alphabet plus punctuations, brackets and a few other randoms. Characters are only 1mm tall. Any smaller and you will start to loose the inside of characters like 'A' and 'B' using the heavy vector setting.
On a light wood like the bamboo the light vector setting seems to work well; while the heavy setting on plastics allow you to paint fill to improve readability.
This character set was based on the free pixel font "Wendy" which you can find here:
I used the font as a initial guide when laying out my line segments. Unlike the pixel font as many lines segments as possible are joined to allow easy scaling to larger sizes.
-Some samples are shown with acrylic paint fills to improve contrast.
-These are only grouped lines, so you'll need to manually place letters onto your design one by one.
Might be something to try out if you want to inexpensively add tiny part numbers or a website/email address to your designs.