Touch-off probe setup and testing!

Here's what I used last time, to investigate how the Centroid touch off features worked. Perhaps there is some intermediate scheme that I can use to mount the probe. Removing the upright from this mag base looks like a good starting point:

Mounting it in a tailstock chuck, then adjusting the probe position looks like a promising approach. Something like this:

Firstly, I need to remove the ball end from the probe tip, as the lump of Bluetack isn't entirely appropriate for the job. Presumably it's a 2mm ball bearing brazed(?) to the end of the probe shaft.

Indeed. It held up well against the angle grinder - until it didn't. The ball itself was as hard as witches' tits until it flew off into the dust and dirt on the floor. Job done either way. This leaves a simple 1.5mm shaft:

I can't find the key (square) stock I know I have somewhere, so finally I gave up looking and went with this 3/8" brass stock. It's a bit larger than I'd planned but I can always replace it later. Meanwhile, I was too impatient to machine it down and instead settled for squaring it off...

...and drilling a 1.5mm hole in the centre.

Yes, I only possess one drill in this size. Don't mess up, Fatty - you only get one chance.

Fits nicely, drill didn't break and a bit of Loctite is ideal for bonding it to the shaft. If I want to replace it, I can simply heat it up with the blowlamp.

And here we are. Yes, the large brass lump looks a bit silly but so what - it will do the business.

Good, so let's give it a whirl. With parameters #281 & #282 set to 9.525mm (aka 3/8") and the "safety clearance" distance reduced to 5mm, we should be good to go.

Here's what I get when I run the Z and X touchoff 3 times (telling it the tool number has changed between events). The offsets seem to vary by ~6um or so. This may be a best case result of course but at least it isn't instantly disappointing.

Let's mount a few different tools in the turret. Then I can touch them off and see what happens when I change tools with the turret and tell the machine to go to the same position in X and Z. 

I will need to issue G43 after each tool change presumably, as indexing the tool doesn't in itself activate the appropriate offset. That's something else to familiarise myself with.

Here we go:
It's early days yet but it seems you don't need a G43 for the lathe, just T0202 etc, to load tool #2 and apply offset #2.

I've now touched off in Z & X (it does them in that order) for the first 4 tools:

• VCGT160404 LH turning tool
• MGMN200 2mm turning / grooving tool
• CNMG120402 LH turning tool
• WNMG080404 LH turning tool

I then set X0Z0 with the DTI reading 2.00mm. Moving to X30 (to clear the moving tools!), then indexing the turret and setting T0202 etc then asking for X0Z0 resulted in the X and Z offsets being correctly applied and the tool tip moving to the intended X0Z0 position. 

Using the Mitutoyo DTI (10um per div), I see tools #2-#4 achieving the same X position, with tool #1 consistently ~50um off. I'm guessing I didn't touch off as accurately for this tool. However, I seem to have sussed out the process and we appear to have a reasonably consistent result.

In practice, the tool change will need to be made with a G28 (tool retract) move, to avoid liquidising the probe, workpiece etc. But for now, I'm testing it out with MDI commands.

No video, it didn't happen of course.