update: got the laser well tuned and focused now. here's a pic of my phone case being engraved. I was concerned about substituting the 8mm hardware with 5/16 inch but it doesn't seem to affect the detail and accuracy of the machine at all.
Thanks for the great Design! I used the remixed bridge pieces that are a bit
shorter to accommodate printing in an Up! Mini with 4.7in. cubic volume, Also substituted 8mm thread and round rod with 5/16 inch rod since I'm in USA and 5/16 is very cheap at the local home improvement store. Having a little trouble tuning the laser but all motion control works smoothly.