Basic CNC Controller, Part 6 - Optional Extra's

Part 6

Optional Extras

 

There are endless upgrade possibilities with this setup. Here are a few:

Adding limit switches:

This is a great safety precaution. Adding limit switches will prevent your machine from overshooting the available limiting travel area. It also allows you to home your machine which means you can stop a job and accurately restart a job if the power is turned off.

The two options of limit switches are mini limit switch with arm or a proximity sensor. Proximity sensors can be used but I will explain how to install a mini limit switch. I would recommend connecting the limit switch with a normally closed contact. This means the switch is normally closed and when the switch is triggered, the contact is opened. This is safer as if the switch is faulty the machine will not move. I highly recommend using shieled cable for limit switched to prevent false triggers. They can become infuriating if they trigger halfway through a cut. Here are links to the mini limit switches and shielded cable: (please note the foil sleeve on the shielded cable must be grounded to earth on the side closest to the controller).

Shielded cable: https://www.cnconline.co.za/products/6-core-0-22mm-mylar-screened-cable

Mini Limit Switches: https://cnconline.co.za/products/mini-limit-switch-pack-of-6

Proximity Sensor: https://www.cnconline.co.za/products/m12-proximity-sensor-npn-nc

 

The connections are as follows: NC on the limit switch must be connected to white side and C on the limit switch must be connected to the black side seen in the picture below.

The following parameters also need to change:

$5=0 for normally open switches

Or

$5=1 for normally closed switches.

$21=1 to enable hard limits

 

Now that you have limit switches you can enable homing

$22=1

$23= (start at 1 and work your way to 8 until your machine is homing in the desired directions)

 

Make sure to test the limit switches with your finger before running your machine into the end stops.

 

The last two optional extras I recommend is an e-stop button and a z-probe.

Link to E-stop button: https://cnconline.co.za/products/emergency-stop-button

Link to Z-Probe: https://cnconline.co.za/products/z-probe

 

The emergency stop button is connected to the E-STOP terminals on the CNC shield and pressed if anything goes wrong. Turn the knob to deactivate the switch.

 

The Z-Probe is used to zero the bottom of your bit with the top of your work piece. There are other ways to zero the bit to the workpiece, but a z-probe is accurate and time saving. The crocodile clip cable is connected to SCL and the touch plate cable is connected to GND on the CNC Shield. If it doesn’t work just flip the two connections around.

 

The crocodile clip is connected to the cutting bit and the touch plate rests on top on the workpiece.

 

Measure the touch probe thickness and input it into the CNCJS software under the probe section. Probe depth represents the distance the machine will probe before error. Probe federate is how fast the machine probes (keep it slow in case there are any issues with the probe and it doesn’t trigger). Retraction distance is the distance the bit retracts after contact with the touch plate. If your software (Vectric or Fusion360) is set to start at 30mm above the work piece and your touch probe thickness is 19,2mm then your retraction distance is 30mm-19,2mm=10,8mm.

If you are happy with the probe settings, you can test by clicking probe. Hold the touch plate in mid air when testing in case something isn’t working correctly.

 

There are many other upgrades and endless upgrade possibilities when using a basic CNC controller. These are just a few basic ones that I found helpful. Good luck with your build and happy CNCing!!