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7x10 Mini-lathe CNC Conversion


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  For a few years now (about 10) I've had a 7x10 mini-lathe from Harbor Freight that has served as my workhorse machine for hobby stuff as well as limited commercial production.  Not a bad machine, with just enough iron to be useful and rigid for "real work."

  I made this CNC conversion in the fall of 1997 after becoming tired and bored with turning the cranks making parts.  The enclosure is a simple Plexiglas box that keeps the swarf and coolants in the machining zone.   A 150 oz-in and 370 oz-in stepper drive the X and Z axes respectively; the X axis is geared 3:1 for extra torque.

  A simple infrared break-beam tab on the spindle provides position and velocity feedback for threading operations.  Read more about CNC threading.

  Since commercial CNC controllers and motor drivers seemed too expensive at the time that I built it, I opted to program my own, which has since evolved into TurboCNC

  In a typical fashion, the stepper motors are driven by pulses from the PC's printer port, with a few extra pins set aside for turning on the spindle and coolant pump, and some other do-dads that I haven't gotten around to building yet.

  It's really a fairly simple arrangement.  I estimate that it took roughly $2000 and 400 man-hours to go from the factory arrangement to the fully converted version.  This includes writing the code for the interpreter, which was a big bottleneck of course.  In terms of actual machine hours, it's probably closer to 50-70 to get the mechanics in place.  Here's a photo of the inside of the controller.

  It's just a few transformers and relays mainly.  The aluminum piece in the lower right is a Faraday shield for an imbedded stepper translator board.  Regular 25 pin printer connectors can be seen entering the box on the upper left if you look closely.  If you're interested, download the schematics for the controller (15k).

  It's probable that 40% of the cost came from tooling and electronics - dwarfing the cost of the lathe in the long run.  I went with Mitsibushi coated carbide inserts and tooling, which can be seen in the picture of the cross slide below.  I've outlined the tool profiles in purple since they're otherwise hard to see depending on your monitor's resolution.  There's a 35 deg diamond on the front and a .093 cutoff blade at the rear, which handles about 90% of everything I do without tool changes.

Since the above photograph was taken, I've added a nicer set of way covers and a quick-change toolpost that takes care of the tailstock tools (drills, boring bars) as well.

Other improvements on the drawing board: (in approximate order of importance)

  • Automatic 5C collet chuck and bar puller for unattended operation
  • Y axis robotic milling spindle (sort of like a 3in1 machine)
  • Pallet changing hardware for loading bar stock

Questions?  Have a look at the CNC lathe FAQ, as the answers to most questions are there.  

  Feel free to drop me a line if you have any questions about this lathe or CNC conversions in general..

 

 

 

 

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This page last updated on July 12, 2011

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