update readme

README.md

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 # 24h Wall Clock
-![Scorch marks for clock face](clock_face_inverted2scorch.svg "Scorch marks for the clock")
+![Scorch marks for clock face](clock.svg "Scorch marks for the clock")
 
+## Why?
 Couldn't find a wall clock design I liked so made my own.
 
-Clock face was designed in OpenSCAD as manually positioning hour segments and applying changes would be very cumbersome. The preview image (`clock_face_inverted2scorch.svg`) was inverted from `clock.svg` with Inkscape.
+## No, but why?
+I like the idea of a timepiece with one revolution per day instead of the one we're used to.
+Clock face was designed in OpenSCAD as manually positioning hour segments and applying changes would be very cumbersome.
+
+
+## Engraving & Cutting with Laser
+As RDworks fails to properly read in the DXF exported by OpenSCAD, a detour through Inkscape is necessary (unless using Lightburn, I presume). If not using RDworks, skip following. From OpenSCAD export as SVG. In Inkscape save the exported SVG as a DXF file. That DXF file can be opened in RDworks.
+
+Tips:
+- Cut against the wood grain, not along (as in + not =).
+- Mask the board with tape (painters or masking tape, the paper kind). This way smoke and soot wont tarnish the board.
+
+On a 100W CO2 Laser With following properties:
+- Engraving layer: 350mm/s@30% power
+- Number edge cutting layer: 50mm/s@10%
+- Outline cutting layer: 25mm/s@45%
+
+Timing
+- Engraving took ~45 min
+- Number edge cutting ~3 min
+- Outline cutting \<1 min
 
 [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/) license.