edits

Urumbu_short_z/README.md

@@ -5,3 +5,7 @@ Below is a short z-axis integrated into the xy machine.  The z axis has about 50
 <img src=./img/z-axis.jpg width=40%>
 <img src=./img/xyz_machine.jpg width=40%><br>
 
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+String up and measure z-axis alone.  First horizontal, with fishing line as belt.  Necessary to adjust bearing position to ease friction on z-travel.  Once that feels good, the plot below is obtained, moving in increments of 32*(1/32) steps eight times forward, then reversing.  Each full step is calculated, using the radius of the capstan, to be 0.31 mm.  Hysteresis is about 0.05 mm.
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+<img src=./img/z_mar08.svg width=40%><br>