Oval slot milling func

o105 sub
   (makes torpedo oval slot from X1,Y1 to X2,Y2)
   (parameters)
   (#1 = X1)
   (#2 = Y1)
   (#3 = X2)
   (#4 = Y2)

   (#5 = slot width)

   (#6 = start depth)
   (#7 = end depth)
   (#8 = depth of cut)

   (globals used)
   (#33 = tool diameter - until this is adapted for proper g41 TC)
   (#35 = safety height)


   #10 = [#3-#1]  (x2-x1)
   #11 = [#4-#2]  (y2-y1)

   (normalise vector)
   #12 = SQRT[[#10*#10]+[#11*#11]]
   #10 = [#10/#12]
   #11 = [#11/#12]

   (scale vector to slot width)
   #13 = [[#5 - #33]/2]  (slot radius - tool radius)
   #10 = [#10*#13]
   #11 = [#11*#13]

   g17 (set XY plane for arcs)
   g40 (turn off TC for now - TODO fix for g41)

   (start at X1,Y1 + right vector {yd,-xd})
   g0 X[#1+#11] Y[#2-#10] Z#35

   #20 = #6  (current depth)

   o115 while [#20 gt #7]

      g2 x[#1-#11] y[#2+#10] i[0-#11] j[0+#10] z#20
      g1 x[#3-#11] y[#4+#10]
      g2 x[#3+#11] y[#4-#10] i[0+#11] j[0-#10]
      g1 x[#1+#11] y[#2-#10]

      #20 = [#20 - #8]

   o115 endwhile

   (last circuit at end depth)
   g2 x[#1-#11] y[#2+#10] i[0-#11] j[0+#10] z#7
   g1 x[#3-#11] y[#4+#10]
   g2 x[#3+#11] y[#4-#10] i[0+#11] j[0-#10]
   g1 x[#1+#11] y[#2-#10]
   g2 x[#1-#11] y[#2+#10] i[0-#11] j[0+#10]

   g0 x#1 y#2  (move clear for extraction)
   g0 z#35     (extract to safety height)

o105 endsub