today i drafted a discussion paper on tool height offset methods

[cnckeith]

******updated 9-18-24*********

https://www.centroidcnc.com/centroid_di ... rement.pdf

today i drafted a discussion paper on tool height offset methods, i got the first three pages done see draft doc below.
the goal here is to explain the three main Methods of tool height offset definition and measurement to give our users guidance in this regard.

I've got a couple more pages in my head about further discussions such as pros and cons of each, absolute encoders, manually measuring with a granite block and caliper, macros, using a touch plate with varying height spoil board, etc.. comments and suggestions are welcome.

and when its done it would be a good story board for a long winded video for those that like to watch vs read.

https://www.centroidcnc.com/centroid_di ... rement.pdf

[Aurelien]

Great job Keith. The same thing for lathe users would really be a big plus for future centroid card purchasers. I'm thinking of investing in a second card for my milling machine and it will help me a lot to get started. THANKS

[RJS100]

Keith, this is very helpful. I currently use the Swissi probe app to measure tool heights and maintain the tool height library. I initially tried using method one. For some reason, most likely operator error, I could not make it work properly. I have been using method 2 for over a year with great results.

I recently posted asking why the Swissi app prompts a warning like your last measured the master tool height was done tool long ago, and needs to be re-measured.

I found this confusing as I understood the master tool height to be of constant, so why the need to re-measure it? Your document points out that the actual measured master tool height may differ if the Z-height is not repeatable. Well done! Thank!

[Aurelien]

keith, I take advantage of your explanation to ask what is the best way to have an extremely precise home Z sensor?
is it all in the choice of sensor? or maybe the approach speed?
What is the most suitable type of sensor?

THANKS

[suntravel]

keith, I take advantage of your explanation to ask what is the best way to have an extremely precise home Z sensor?
is it all in the choice of sensor? or maybe the approach speed?
What is the most suitable type of sensor?

THANKS

I have less than 0.003mm deviation with a cheap NPN sensor, but I drive to the face of the sensor.

Mechanical is Balluff top notch, but expensive:

https://www.balluff.com/de-de/products/BNS004U

Uwe

[midy]

Great job Keith. The same thing for lathe users would really be a big plus for future centroid card purchasers. I'm thinking of investing in a second card for my milling machine and it will help me a lot to get started. THANKS

Seconded, a similar thing and even an in depth video for lathe users would be great! I've been trying to set things accurately for a while now and although i'm getting there, help from the experts would be great!

[cnckeith]

Keith, this is very helpful. I currently use the Swissi probe app to measure tool heights and maintain the tool height library. I initially tried using method one. For some reason, most likely operator error, I could not make it work properly. I have been using method 2 for over a year with great results.

I recently posted asking why the Swissi app prompts a warning like your last measured the master tool height was done tool long ago, and needs to be re-measured.

I found this confusing as I understood the master tool height to be of constant, so why the need to re-measure it? Your document points out that the actual measured master tool height may differ if the Z-height is not repeatable. Well done! Thank!

the reference tool method requires the reference to be set by the reference tool each time the machine is power cycled. this is because the home position could change or even the reference position itself, as long as you retouch the reference tool it doesn't matter since the reference tool method is measuring the difference between the ref tool and the actual tool, not an absolute value based on a fixed position like method 1

[cnckeith]

thanks for the feed back i will keep expanding the document to address all questions

[cnckeith]

Great job Keith. The same thing for lathe users would really be a big plus for future centroid card purchasers. I'm thinking of investing in a second card for my milling machine and it will help me a lot to get started. THANKS

thanks, i'll cover lathe as well, it is pretty much the same. but, i'll make drawings for a lathe so it is clear!

[cncsnw]

You might also want to clarify that the prerequisites for using Z Home as Z Reference are both repeatable Z homing, and a fixed table height.

A knee mill with a closed-loop control -- which finds home using a switch combined with the encoder index pulse -- has entirely repeatable Z axis homing, but generally requires a physical reference tool because the tool measuring surface (the table) can move up and down.