HUM, the stored value will be at the point the slack is taken up in the mechanism and the contact opens. Then Mach3 slows to a stop.

Connect an ohm meter from the tool tip to the contact plate. Step jog up to the plate until the omh meter just shows contact. Zero Z then step jog further until the PROBE LED lights up. That is the switch motion you also have to account for. Once found add it into your tool probe routine.

Just a thought, (;-)TP

Good thinking Terry – I gave it a try first thing this morning.

My Z axis moves in steps of  0.001875mm (but the accuracy of micro steps are a long standing point of discussion).

Jogging with Mach set at 0.0010mm step size and zeroing at the exact point of electrical contact a further 2 steps were required to trigger the probe with the DRO reading -0.0037mm.

Tweakie.

(but the accuracy of micro steps are a long standing point of discussion).

My testing has indicated that it can be influenced greatly by the motor. All depends how the Earth and Moon
align given a place in orbit.

So you may want to try a number of locations along the rotation and take an average.

FWIW,
RICH

So you may want to try a number of locations along the rotation and take an average.

Good point Rich. 

Tweakie.

A little more progress - This is the over-travel limit switch, well 3 switches actually but they are connected in parallel and operate on the 'first home' principle.

The total thickness, including the PCB, is 2mm and this assembly fits beneath the the contact plate (in the base of the probe) and will activate a limit input if the G31 probing routine failed.

The probe will continue to use the 3 wire connection to the machine and additional circuitry has now been fitted, at the breakout board end, to detect probe circuit continuity. This effectively signals a 'Probe Already Grounded' condition to the probing routine if either the positive or GND connecting wires are disconnected or if the probe is not actually connected to the machine. This added 'fail safe' feature was considered necessary because I am signalling the over-travel limit through the two supply wires.

Hopefully, I have now covered every eventuality but life always seems to punish the complacent and so 'time will tell'. 

Tweakie.

Very nice Tweakie, can`t wait till you finish. I am sure it will be awsome, I would love to make one as well.

Very nice Tweakie, can`t wait till you finish. I am sure it will be awsome, I would love to make one as well.

Hi Astroguy,

Thank you.

I keep making minor alterations to the basic design (from experience gained and others suggestions) but I am nearly there.
I have almost compiled a complete set of drawings and GCode files but this seems to be taking longer than it took to make the original parts. 

Tweakie.

Any progress? The suspense is killing me.

Hi Astroguy,

Sorry for the delay.

By including the over-travel switch, the wiring between this and the main panel makes it difficult to dis-assemble / re-assemble so the case has been re-designed to include a pocket to accommodate a wiring loop and I have just not been able to get the time to test the tool path for the new case yet.
The control board PCB has yet to be laid out and I am still awaiting delivery of some low current opto isolators from China - it is all work in progress. 

Tweakie.

NOW to add something to think about the amount of over travel of the probe will depend on your accelleration settings. SOME systems have very slow Accel and need lots of room to stop. HOW much overtravel does the machine normally have. Do you have enough overtravel in the probe design (before it hits the overtravel limits ??  IF not on fast probing you may trip the OTlimit.

Just a thought, (;-) TP