Finishing Parts: Engine Turning

Adding a finish to your parts isn’t always vital, but it is certainly one of the more entertaining parts of machining. For those who are looking for a finish that is arguably one of the most classic, engine turning will add a unique sheen to your parts. 1024px-Charles_Lindbergh_and_the_Spirit_of_Saint_Louis_(Crisco_restoration,_with_wings) One of the most recognizable displays of engine turning was seen on Charles Lindbergh’s famous aircraft, the Spirit of St. Louis. Engine turning can be done in a number of ways, but we utilized a Tormach Tension/Compression Tapping Head and some Cratex Rods that we picked up from an industrial supplier. Since the rods are an abrasive material and we did this process in aluminum, we used an extra fine grit – heavier grits would be recommended for harder metals like steel. Craytex-Machine-Turning-Rods-IMG_6585 We wrote a G-code program by hand to create the engine turning pattern on a block of aluminum. This specific G-code program uses subroutines, which some users may not have seen before. For more information on subroutine programming, please see Chapter 7 of the Tormach Operator’s Manual or CNC Cookbook’s post on subroutines. *This G-code is for sample purposes only – Tormach Tech Support cannot help you debug code.

  • #<_x_start> = 0
  • #<_y_start> = 0
  • #<_x_stepover> = .25
  • #<_y_stepover> = .25
  • #<_x_distance> = 3.25  (part width in x)
  • #<_y_distance> = 2.5   (part depth in y)
  • #<_x_repeat_count> = [FUP[#<_x_distance> / #<_x_stepover>]] (FUP will round up to nearest integer value)
  • #<_y_repeat_count> = [FUP[#<_y_distance> / #<_y_stepover>]]
  • #<_x_retract> = [#<_x_repeat_count> * #<_x_stepover>]
  • #<_z_depth> = -.1      (how far to compress the tapping head)
  • #<_z_retract> = .2
  • #<_dwell> = 1         (how long to dwell in seconds)
  • #<_z_feed> = 20
  • #<_spindle_rpm> = 2500
  • O100 (engine turning sub – handles Z motion and dwell at one X/Y location)
  • G1 Z#<_z_depth> F#<_z_feed>
  • G4 P#<_dwell>
  • G0 Z#<_z_retract>
  • M99
  • O101 (move over one stepover in X)
  • G91  (change to incremental coordinates)
  • G0 X#<_x_stepover>
  • G90  (back to absolute coordinates)
  • M99
  • O102 (engine turn one point, then move over one stepover)
  • M98 P100
  • M98 P101
  • M99
  • O103 (complete one entire row in X)
  • M98 P102 L#<_x_repeat_count>
  • G91 (change to incremental coordinates)
  • G0 X-#<_x_retract>
  • G90 (back to absolute coordinates)
  • M99
  • O104 (do one X row, then increment Y)
  • M98 P103
  • G91 Y#<_y_stepover>
  • G90
  • M99
  • O105 (main program)
  • G54 G20 G90 (safety block)
  • M3 S#<_spindle_rpm>   (spindle on)
  • G0 X#<_x_start> Y#<_y_start> Z.2
  • M98 P104 L#<_y_repeat_count>
  • G30 (move to G30 position)
  • M30

How have you finished your parts? Comment below or email us pictures at

Craytex-Machine-Turning-Rods-IMG_6646 Craytex-Machine-Turning-Rods-IMG_6601 Craytex-Machine-Turning-Rods-IMG_6613

We used more abrasive pads to give a similar appearance in steel.
Finishing with some more abrasive materials in steel.


Chris Fox

Chris comes from a publishing background with years of experience in science, technology, and engineering publications. Previously an editor with Product Design and Development and Gizmag, he has a keen eye on the maker community and the changing landscape of the world of prototyping, product development, and small-scale manufacturing. Chris has been working with clients to create Tormach's customer success stories since 2013. Follow him on Twitter @TheChris_Fox

Chris Fox

2 thoughts on “Finishing Parts: Engine Turning

  • Avatar
    04/20/2016 at 4:12 pm

    What happens when you get out at the edge of a part? Are those Cratex rods rigid enough to handle hanging out over the edge or is it going to tend to bend the rod and push it off the part? I’m wondering if I need to do the jeweling operation before I cut my outer part profile or if I can wait to do the jeweling until the part is otherwise complete?

  • Chris Fox
    04/20/2016 at 4:30 pm

    Hey harley573, thanks for reading! We ran just a touch over the edge of the part and the Cratex held up just fine, but I wouldn’t recommend going past half the diameter – you might get some bending at that point. As long as you stick to that rule-of-thumb, you should be able to do the jeweling before or after you do the part profile.

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