qtdragon - probing issues

cmorley wrote:

There is m70/m72 that can do the recording/restoring, not sure how it works with errors.

It certainly claims to restore on exit. Whether it does on error exit is something I haven't tried experimenting with.

Does this seem right/reasonable to you?

Yes, and going back to the previous units is better than what I implemented in the probescreen_ng code.

By physical latch distance, are you referring to the small distance the probe internal mechanics must move to make/brake the contact? sounds right.
well, I have 3 different probes. the one I referred to above is a Tormach brand a couple years old (no longer sold). I have one from Drewtronics, a small US manufacture, and an inexpensive Chinese one.
I'll try each and watch the results very carefully.

As for calibration, qtdragon VersaProbe does not have a routine for that. Probe Basic does, but I'm not sure how it operates, or if it is correct or not. I have done some searching for calibration routines and have found a few. So far they are primarily accounting for off-centerness.
Wish I had one of those super good Renishaws.

The mechanical latch distance (and associated time) goes into what Rodw was speaking about.
And it's good to see AndyP joining in.

Let's keep at it.

I think that calibration is generally looking at the lobularity of the detecting circle, as the three-bar contacts mean that the probes trigger fractionally earlier in some directions that others.

When I made my probes  I planned to write a calibration scheme that used the spindle encoder. (as my tooling only fits into the spindle in a fixed orientation). The idea was to probe a test ring, then turn the spindle approximately 90 degrees and probe again. From the exact angle turned and the difference in X and Y centres of the two measurments you can derive a correction fr any spindle angle (as read by the encoder). .
This might be a bit specific to my machine, as there is an absolute spindle encoder and tooling that only fits in one orientation.
 

well, interesting word that is. but you're definitely correct. since the vast majority of probes are based on a 3 legged stool concept, there is most certainly a small difference in activation.
I try to install my probes into the spindle in the same direction such as the connecting cable always out the left side (-y direction). if I probes diameters only in the 3 contact directions, it might help. but then what about corner probing.... or arbitrary directions like with your perimeter probing routine...... oh well.
just one more nuance to add to the bag.

cmorley wrote:

I would think that the physical latch distance must be accounted for.
When the probe touches the material, it doesn't trip right away.
You must move enough to break the contact.
 

This is why I think G38.4 probe away will yield more accurate results.

The probe signal won't be triggered (on lost contact) until the probe is back sitting on its 3 legs
​​​​and a much lower speed can be used for those few microns so the distance travelled in a servo cycle thread is much less.
In theory you should be left with the lobularity error plus the distance  per servo cycle which should be in sub microns (which can be slower)

We always  probe away on the final probe move on plasma cutters when probing for the surface.
And we do account for switch/probe hysteresis but using a probe away strategy and an ohmic (electric contact) probe basically eliminates the hysteresis.

ya never know 'til ya try it.
i'll see if I can modify the famous p-hole.ncg (by cradek)
it does a double touch. i'll try and change the 2nd touch to a G38.4 and checkout my bearing diameter again. maybe it'll get more accurate.....