Right, this post is technical. If you don’t know what a datum is it’s time for some education.

My understanding of a datum is a point which is referred to, now when that comes to milling it could be the corner of stock, it could be a hole within your model.

Recently I was milling some aluminium and I needed to change heads through the milling process, however when you change the mill bit it might be a fraction longer than the one you were using – so how do you ensure you find the correct height each time. What if you want to mill the top then bottom of stock – your very unlikely to be able to put the stock back in the same place each time. SO HOW DO YOU DO THIS?

You use a datum!

The shapeoko 3 has a port for probing – the axis moves to certain point or till the two contacts are touched. If you have your probe attached to the mill end it will stop when it hits grounded material.

Not all material can be ground – for instance wood.

So I knocked up an aluminium probe that sits on the corner of stock. You can probe to three axis each time setting them to zero then minus 31mm from X/Y and 5mm from the Z this will find the same point each and every time and is accurate up to 0.2mm (and thats down to my milling skills).

I made the probe from 10mm aluminium stock, a crocodile clip and some wire… All in it cost about £3 but will save me a future in botched jobs and time wasted.

Here is the probe.


This is the probing command – Gcode – G38.2 z-100 F150 for the other edges X/Y you would just change the Z to the axis you want to move.

Here is a video of it in action.