Calibrate unit after some changes

[ri0t]

Since the lens has been exchanged with the big one and the tube mounts have been changed for better 3d printed ones, the thing needs to be calibrated again.

• [x] Fix (currently loose) tube mounts in right position. Make sure,
  • [ ] the primary mirror has no shims
  • [ ] everything is at the right height and horizontal
  • [ ] beam hits the center of the mirror
  • [x] tube is vertically parallel to the case's rear wall
• [x] Adjust first mirror. Make sure,
  • there are no unnecessary shims below the secondary mirror's mount
• [x] Adjust secondary mirror. Make sure,
  • NO SHIMS on third mirror / focus system
• [x] Do check if all corners work
• [ ] Adjust focus to engraving length
• [ ] Generate/Aquire and finally engrave test pattern (#21)
• [ ] Adjust focus to cutting length
• [ ] Proceed to cut focus tool (#20)

[ri0t]

Very good guide from the manufacturer: https://omtechlaser.com/blogs/news/laser-engraver-mirror-alignment-how-to-align-a-co-laser-beam