What's the best method for automatic depth setting?

I am using a precision micro switch to do depth setting. It is accurate to +/- 3 microns (this one D5A-8511). I am finding that my repeatability (is that a word?) is off in the Z direction by a thou or 2.

My method is to lower on the switch at 25 ipm until the switch triggers,
then back off in a rapid move .15 inches, then lower at 5 ipm until it triggers, save position,
then back off in a rapid move .15 inches, then lower at 5 ipm until it triggers, save position,
Take the average of the 2 positions, and set this as my height.

Sometime chips get on the switch which really messes it up, so I was planning to add a blow off nozzle, But then I got to thinking maybe there is a better way.

I used the switch so I didn't need to worry about adding a wire to the bit. With my ATC my goal is to let the machine do it's thing while I'm doing other stuff.

What is the best way to set depth? A different switch or a different method with the switch I have?

You say ''lower to the switch'' Normally you contact the home switch going up. That way gravity is working for you by pulling down on the axis. Going up helps overcome any backlash and stiction. I would not rapid off of the switch, maybe come off at 5 IPM then reverse direction at about 1 IPM for the final move.

With a +/- 3 micron switch, you should be able to hit +/- 3 microns.

This is not the home switch, this is a different one used only for depth setting. My home/limit switches are set about 1/2" from the hard stops. The depth setter switch is on the table.

Ahhh. You might change your setting routine to 1) Down to the switch at 25 IPM, 2) back off at 5 IPM, 3) approach switch again at 1 IPM and over travel to whatever your switch will safely take, 4) then back off at 0.5 IPM until the switch changes state, 5) stop and log position.

That is an interesting idea I hadn't thought of checking the on to off state. I'll have to do some testing.

No picture of your switch installation. I mention that because how the switch is actuated is a big part of repeatability.


In the distant past I made use of a Baumer My-Com switches. Th switches are great but if you don’t get the mechanical mounting right you will not leverage their high precision. Which brings us to the next issue; your repeatability issue might not have anything to do with the switch. For many DIY machines 0.001”’is a lot to expect out of the machine.