o<npt_pipe> sub
   (standard NPT subroutine)
   (npt_pipe.ngc)
   (Based on formulas in Machinery's Handbook)
   (June 4, 2016     - written by M Kennedy)
   (r1 July 12, 2017 - added linear cut depth regression, removed factored regression)
   (r2 Jan 2, 2020   - fixed small bug around thread depth calcs)
   (r3 Jul 16, 2021  - fixed bug around thread depth calc and X0 calc)

   (Change these values. Get from Machinery's Handbook, or use Nominal size to look up in table below)
   (Program assumes that Z=0 located at end of pipe to be threaded)
   #<_OutsideDiameter>    = #1 (Nom or Act Dia, D)

   (Don't usually have to change these values)
   #<_TPI>		  = #2 (=0 TPI, 0 for auto)
   #<_First_Cut_Depth>	  = #3 (=0.015 First Cut)
   #<_Minimum_Cut_Depth>  = #4 (=0.003)
   #<_X_Clearance>        = #5 (=0.075 X clearance)
   #<_Z_LeadIn>           = #6 (=0.250 Z Leadin)
   #<_TipRadius>          = #7 (=0.003 Tip Radius)
   #<_Spring_Passes>      = #8 (=1 Spring Passes)
   #<_CompoundSlideAngle> = #9 (=29.5 Angle, 0-30)

   (check to see if tool set)
   o100 if [#5400 EQ 0]
      (msg, Tool not set)
      M2
   o100 endif

   (auto TPI detection if nominal pipe size entered)
   o250 if [#<_OutsideDiameter> EQ 0.0625]
      #<_OutsideDiameter> = 0.3125
      #<_TPI> = 27
   o250 endif 
   o300 if [#<_OutsideDiameter> EQ 0.125]
      #<_OutsideDiameter> = 0.405
      #<_TPI> = 27
   o300 endif 
   o305 if [#<_OutsideDiameter> EQ 0.250]
      #<_OutsideDiameter> = 0.540
      #<_TPI> = 18
   o305 endif
   o310 if [#<_OutsideDiameter> EQ 0.375]
      #<_OutsideDiameter> = 0.675
      #<_TPI> = 18
   o310 endif 
   o315 if [#<_OutsideDiameter> EQ 0.500]
      #<_OutsideDiameter> = 0.840
      #<_TPI> = 14
   o315 endif
   o320 if [#<_OutsideDiameter> EQ 0.750]
      #<_OutsideDiameter> = 1.050
      #<_TPI> = 14
   o320 endif 
   o325 if [#<_OutsideDiameter> EQ 1.000]
      #<_OutsideDiameter> = 1.315
      #<_TPI> = 11.5
   o325 endif 
   o330 if [#<_OutsideDiameter> EQ 1.250]
      #<_OutsideDiameter> = 1.660
      #<_TPI> = 11.5
   o330 endif 
   o335 if [#<_OutsideDiameter> EQ 1.500]
      #<_OutsideDiameter> = 1.900
      #<_TPI> = 11.5
   o335 endif 
   o340 if [#<_OutsideDiameter> EQ 2.000]
      #<_OutsideDiameter> = 2.375
      #<_TPI> = 11.5
   o340 endif
   o345 if [#<_TPI> EQ 0]
      (msg, need to input TPI)
      M2
   o345 endif 

   (Calculations)
   #<Pitch> = [1.000488 / #<_TPI>] (correct for tapered drive line)
   #<E0> = [#<_OutsideDiameter> - [0.05 * #<_OutsideDiameter> + 1.1] * #<Pitch>] (Pitch Dia at beginning of external thread)
   #<L2> = [[0.80 * #<_OutsideDiameter> + 6.8] * #<Pitch>] (Effective thread length)
   #<V> = [#<Pitch> * 3.47] (Vanish thread length)
   #<ThreadDepth> = [#<Pitch> * 1.515 - 2 * #<_TipRadius>] (diameter thread depth from pitch dia)
   (increase Z Leadin slightly so that _Z_Leadin + L2 is a whole number of threads)
   #<_Z_LeadIn> = ABS[[[FUP[[#<L2> + #<_Z_LeadIn>] / #<Pitch>]] * #<Pitch>] - #<L2>]

   (calculate coordinates for G33 cuts - X0,Z0 small end, X1,Z1 at effective thread length, X2,Z2 at end of threading)
   (start of pipe at Z=0)
   (Z0, X0 are absolute. other X, Y are relative)
   #<Z0> = #<_Z_LeadIn> (taper starts at leadin)
   (X max to E pitch dia is 1/2 * H. Since Hdiameter = 1.732 * Pitch, this is 0.866 * Pitch)
   #<X0> = [#<E0> - [#<Z0> / 16] - [0.866 * #<Pitch>] + [2 * #<_TipRadius>]] 
   (Z1, X1 are relative to Z0, X0.  Z2, X2 are relative to  Z1, X1)
   #<Z1> = [#<L2> + #<_Z_LeadIn>]
   #<X1> = [#<Z1> / 16] (taper is 1/16 on dia)
   #<Z2> = [#<V>]
   #<X2> = [#<_OutsideDiameter> - #<X0> - #<X1>]

;(debug, L2=#<L2> V=#<V> pitch=#<Pitch>)   
;(debug, E0=#<E0> Z0=#<Z0> X0=#<X0> Z1=#<Z1> X1=#<X1> Z2=#<Z2> X2=#<X2> ThreadDepth=#<ThreadDepth>)
;M2

   G7 G18 G20 G54 G90 G94
   G95 (feed per revolution mode)
   M3 (dummy command required for G33)
   F1 S500 (dummy command required for G33)

   (initialize loop parameters)   
   #<CutDepth> = #<_First_Cut_Depth> (current cut depth)
   #<XX> = [#<_OutsideDiameter> - #<CutDepth>]                       (XX is current cut depth at location of X0, Y0)
   #<ZZ> = #<Z0>                                                     (ZZ is current lead in)
   #<ZStepover> = 0 (offset between passes)
   
   (main cutting loop)
   o200 do
      (rapid to safe start)
      G0 X[#<_OutsideDiameter> + ABS[#<_X_Clearance>]]
      G0 Z[#<Z0>]
      (make tapered cuts)
      G1 X[#<XX>] Z[#<ZZ>]                                               (start point)
      G33 X[#<XX> + #<X1>] Z[#<ZZ> - #<Z1>] K#<Pitch>                    (cut effective thread)
;(debug, CutDepth=#<CutDepth> XX=#<XX> OD=#<_OutsideDiameter> TD=#<ThreadDepth>)
      o210 if [[#<XX> + #<X1>] LT #<_OutsideDiameter>]
         (only run if cut to be made)
         G33 X[#<XX> + #<X1> + #<X2>] Z[#<ZZ> - #<Z1> - #<Z2>] K#<Pitch>    (cut vanish thread)
      o210 endif
      o220 if [#<XX> GT #<_OutsideDiameter> - #<ThreadDepth>]
         (take deeper depth cuts initially until cut depth is more than thread depth)
         #<CutDepth> = [#<_Minimum_Cut_Depth> + [#<_First_Cut_Depth> - #<_Minimum_Cut_Depth>] * [#<ThreadDepth> + #<XX> - #<_OutsideDiameter>] / #<ThreadDepth>]
      o220 else
         #<CutDepth> = #<_Minimum_Cut_Depth>
      o220 endif
      #<ZStepover> = [SIN[#<_CompoundSlideAngle>] * #<CutDepth>]

      (next cut, check for spring passes)
      o240 if [#<XX> GT #<X0>]
         #<XX> = [#<XX> - #<CutDepth>]
         #<ZZ> = [#<ZZ> - #<ZStepover>]
      o240 else
         (spring passes)
    	 #<XX> = #<X0>
	 #<_Spring_Passes> = [#<_Spring_Passes> - 1]
      o240 endif
	  
   o200 while [#<_Spring_Passes> GT -1]

   (move back to starting position)
   G0 X[#<_OutsideDiameter> + ABS[#<_X_Clearance>]] 
   G0 Z[#<_Z_LeadIn>]
   M5
   M2
o<npt_pipe> endsub