%
(Cutter runs outside the rectangle)
(The origin is at the centre of the rectangle)
(Z=0 at the top surface)
(Position the Controlled Point above the centre of the rectangle)
(before using this program)

(#80 holds the length of the rectangle)
(#81 holds the width of the rectangle)
(#82 holds the final depth of cut)
(#83 holds the depth of cut at each pass)
(#84 holds the cutter diameter)
(#85 holds the Safe Z height)

(#90 will hold half the length of the rectangle)
(#91 will hold half the width of the rectangle)
(#92 will hold the current depth of cut)
(#93 will hold the number of passes)
(#94 will hold half the length of the toolpath)
(#95 will hold half the width of the toolpath)

O300 sub (Subroutine to cut around the periphery)
(Position the cutter at the left front corner - F,) 
G0 X[-1*#90] Y[-1*#95]
(Cut vertically to set the depth)
G1 Z#92
(Cut the straight part of the length, to G)
G1  X#90 Y[-1*#95]
(Quarter circle around the corner, to H)
G3 X#94 Y[-1*#91] I0 J#84
(Cut the width, to K)
G1 Y#91
(Quarter circle around the top right corner, to L)
G3 X#90 Y#95 I[-1*#84] J0
(Same for the next width and corner, to M then N)
G1 X[-1*#90]
G3 X[-1*#94] Y#91 I0 J[-1*#84] 
(Down to P, then around to F)
G1 Y[-1*#91]
G3 X[-1*#90] Y[-1*#95] I[#84] J0
(Add the extra depth of cut in preparation for the next cut)
#92=[#92 + #83]
O300 endsub  


(Main program)
(initialisation block)


#80 = 100 (Set the length)
#81 = 50 (Set the width)
#82 = -22 (Set the final depth of cut)
#83 = -5 (Set the depth at each pass)
#84 = 5 (Set the cutter radius)

(Set the Safe Z height)
#85 = 10

(Calculate half the length of the rectangle)
#90 = [#80/2]
(and add on the radius of the cutter to find half the length of the toolpath)
#94 = [#90 + #84]

(Calculate half the width of the rectangle)
#91 = [#81/2]
(and add on the radius of the cutter to find half the length of the toolpath)
#95 = [#91 + #84]

(Set the initial value of the current depth of cut)
#92 = #83

(Calculate the number of passes of the cutter)
(to get as close as possible to the final depth)
(without cutting below the final depth)
#93 = FIX[#82/#83]


(Make this point -at the centre of the rectangle- 0, 0 temporarily)
G92 X0 Y0

(Set the feed rate)
F100

(Now loop around the periphery)
O400 Repeat [#93]
O300 call (calls the subroutine to cut around the periphery)
O400 endrepeat

(Final pass at full depth)
#92 = #82 (Make the current depth of cut = the final depth)
(Then perform the final pass just once)
O300 call
(Go back to the temporary origin)
G0 X0 Y0
(Now restore the original co-ordinates)
G92.1

M30
%