Why Manual CNC Is A Bad Idea

Crushed tool length probe switch
Crushed tool length probe switch

Most of my machining involves one-off setups and simple cuts, so I usually type G-Code directly into EMC2’s Axis interface: CNC hits precise locations and makes smoother cuts than I ever could. Most of the time, that works really well.

Occasionally, though, I think one thing and type something else.

Just a typo, happens all the time…

Better, of course, to write a little program and debug it, but then a simple task starts to look a lot like work.

Fortunately, I have a bunch of those switches on hand.

9 thoughts on “Why Manual CNC Is A Bad Idea

    1. Truth be known, I’ve been hammering out G-Code by hand for my projects… that’s how simple they are!

      Some useful G-Code generator routines for simple tasks live on the EMC2 wiki. If you already have a drawing, then something from their list of CAM programs may be useful.

    2. Inkscape gcodetools will allow you to export 2d drawings as gcode. Eagle and gEDA both have gcode plugins that’ll allow you to export pcb’s directly to your mill.

  1. I’ve been thinking about building a tool length probe switch based on your previous posts, and last night was looking in my junk box. I have a bunch of microswitches with long steel contacts. I was thinking about attaching a line to the steel contact, and driving the z axis down fast until I see an electrical contact, then stepping down until the switch itself trips, to avoid just exactly the situation you ran into here. Any thoughts?

    1. driving the z axis down fast until I see an electrical contact

      It turns out that the oil in the spindle bearings does a great job of insulating the tool from all the convenient non-rotating parts of the head. Having to remember to attach an alligator clip to the spindle before probing should demonstrate the limits of human memory; I know how it’d (not) work for me…

  2. The steel contact will chip the hell out of your carbide cutters, and even HSS ones it will do no favors. IMHO.

  3. I managed to break a $300 tapping head on our VMC with a typo like that, happens faster than you can blink often enough.

  4. I’m amassing a small pile of exhibits for my museum of “Don’t do what I did”… bent 1” drill bit, bent edge finder, I’ve not had the courage to try my Renshaw TP-1 touch probe I bought on ebay after Mach3 dragged it over the surface of the skate board I was digitizing… One of these days (probably after I break something else important to me) I’m going to rig up something in Mach3 that will activate a relay while probing, switching the probe input signal from the e-stop line to the probe input. That way if I accidentally activate whatever I’m probing when doing a G0 it will hopefully stop instead of smashing something!

    – Steve

    1. my museum of “Don’t do what I did”

      “It was said of him that he never made the same mistake twice, but nobody could remember when he’d made a mistake for the first time.”

      switching the probe input signal from the e-stop line to the probe input

      IIRC, EMC2 has a HAL function that halts motion when the probe closes during anything other than a probe operation. Obviously at least one of these is true:

      • That’s not engaged in my lashup
      • I (once again) remember incorrectly
      • Something (else) went horribly wrong

      I obviously should figure that out…

Comments are closed.