divide step downs for shadowline helps with small parts

notes.md

@@ -2,7 +2,8 @@
 
 ## 2.3 remaining
 * adaptive shadow-line generation for small parts collision detection
-* test path clearance for every move > % of tool diam and ...
+* step down should interpolate top/bottom again
+* preview rendering bugs for contouring
 * path arrows, retracts, and engages
 * cap path ends
 * help dialog

src/mode/cam/slice.js

@@ -59,7 +59,7 @@
             ztOff = hasStock ? proc.camZTopOffset : 0,
             camRoughStock = proc.camRoughStock,
             camRoughDown = proc.camRoughDown,
-            minStepDown = Math.min(1, roughDown, outlineDown),
+            minStepDown = Math.min(1, roughDown/3, outlineDown/3),
             maxToolDiam = 0,
             thruHoles;