end stop selection

Hi,

I'm building a CNC milling machine and I am at the stage of choosing what kind of device to use for end-stops. My main criterion is accurate and repeatable homing of the machine.

I have some good quality mechanical switches as a first option but want to know whether and what kind of proximity detectors could provide better results.

I have experience of Hall effect sensors which are used on BMW motors for ignition timing but they are a rather costly solution. Basic searching reveals various claims of inductive proximity detectors which are very price competitive and likely more repeatable than mechanical switches. Apparently axial format are generally less precise.

I see that many reprap constructions use an inductive device on Z only since this the main one requiring accuracy on a 3D printer. On a CNC mill, all axes require the same precision.

can anyone provide specific, data backed information preferably with some kind of product reference rather than airy generalities?

TIA.

No generalities. Are you going to write your own CNC software? Most people would use what ever the electronic control boards are designed for.

Paul

I am using micro switches with a little wheel at the end of the lever (less friction) for my CNC machine.
Normally closed (switch opens when activated), for higher reliability.
Homing accuracy (three axes) has never been a problem.
A 3mm bit ends in a 3mm pilot hole every time.
Homing also depends on the software.
My CNC moves 'till the switch opens, and then steps back until the switch closes again.
That point is the home position.
Leo..

Wawa:
I am using micro switches with a little wheel at the end of the lever (less friction) for my CNC machine.
Normally closed (switch opens when activated), for higher reliability.
Homing accuracy (three axes) has never been a problem.
A 3mm bit ends in a 3mm pilot hole every time.
Homing also depends on the software.
My CNC moves 'till the switch opens, and then steps back until the switch closes again.
That point is the home position.
Leo..

My CNC selective soldering machine does exactly the same with the same switches. My home CNC milling machine does not uses home switches. The software home is at some given surface of the material being milled. One home for each axis.

Paul

Have added the homing switches myself, and a laser cross, so I have more than one option to setup/zero the machine. Homing switches also can protect from accidental hitting the mechanical limit(s), e.g. the Z-axis. I have added the limits in the Mach3 software.
Leo..

The software home is at some given surface of the material being milled.

That is not a "home" position. It is a temporary zero for the work-piece. ie you are not using homing at all. The local zero is semi-arbitrary , non repeatable. You just power on, jog to the metal and call it zero.

Accuracy does not matter in that context. It's just a starting position for the cut.

That is one approach.

Homing accuracy (three axes) has never been a problem.

seems to be saying the same thing.

This all assumes that you never need to restart a job. You start a cut and continue until the piece is finished.