Backlash probe for Mach 3

As a result of struggling with backlash issues much longer than needed I built this probe and wrote a small VB procedure to help read backlash values within seconds. The probe is similar to edge finder which rises a bit on the parallel interface when grounded. The electrical connection is made between the probe and the spindle using two alligators and required an isolated base which is made of clear Polycarbonate. At the base are two rare earth magnets which holds the probe on the milling vise or alternatively between its jaws. The audio jack plugs into a connections box which leads it to the controller.

The script is self-explanatory, just notice the settings under “User Inputs” and make sure to select the correct values:

Resolution – If you need an immediate low-res (i.e. non-accurate) backlash reading you can run at 10 or 100 and the feed rate will be set respectively (the resolution will be low but the speed will be high). For final reading always use 1000.

Active Axis – Simply set to X, Y or Z and place the spindle (or tool or whatever is attached to the spindle) between probe’s brackets, somewhere in the middle, and in a way that will allow the brackets to touch the spindle when the axis moves in both directions.

Two Sides – This is useful for Z but can be used on any axis. When measuring backlash I always read it in two directions and set the average result as backlash compensation. With X and Y there should be no problem, but when doing Z, how do you set a tool to touch the two brackets of the probe? You can use any tool such as fly cutter, a bit with extended tip or a hex wrench attached to a drill chuck. Otherwise, you can set this parameter to False and the script will run the axis in one direction, which is going down to the table.

Number of loops – For some reason I initially wrote the script with an option to run multiple cycles and display the average reading but I never used it and always run once. It is there in case you find it useful.

The code can be found here, open the VB editor and paste it there. Always remember to “SAVE AS” or else Mach 3 might use a previously stored file name and overwrite existing file you may need.

How to hold the probe for XY (right) and Z (left)


14 thoughts on “Backlash probe for Mach 3”

  1. Will this script run for ths X axis without any modification? I tried it and the X axis moved in one direction to the fixture then shot off at full G0 speed in the opposite direction. There must be a setting I’m missing.

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