Laser tool setter for The Shiz!

Wow, lasers in da shop?

For a few years now, I've been using a Renishaw TS27R tool setter for touching off tools in The Shiz. 

This is a massive timesaver and allows pretty accurate tool length measurement, which is rather important if you want to be able to change tools in the middle of a job without incurring errors due to a change in tool length - touching off against a fag paper or an accurate gauge (eg a 10mm broken end mill) is OK but takes a bit more messing about.

In Centroid CNC12, there's a pretty nifty extension called CHIPS that was developed by "Swissi" (Roland Kunz) that automates the process of measuring tool offsets and saving them to the tool library. In conjunction with a tool setting probe such as the TS27R, the process is wonderfully simple and quick.

One drawback of CHIPS to date has been that it only measured tool length offsets, not tool radius offsets (due to wear, tolerance and runout). However, a recent update has extended the CHIPS capability to include automatic tool radius offset measurement. This is generally done with a rotating tool, as many (most) tools have multiple flutes or inserts. Although the TS27R is intended to be capable of this kind of operation, it requires the CNC controller to have that functionality. Now it seems we have that available in the latest version of CHIPS when combined with the massive update of CNC12 to version 5.4.

Enough. Show me the lasers.

Rather than require an exotic (= expensive) toolsetter such as the TS27R, the recommended solution developed by Uwe (another CNC12 user / developer) is a "laser fork" sensor. This uses a laser beam to detect the tool, rather than contact with a setter. 

I have to say, approaching the TS27R with a spinning face mill would be a bit of an act of faith. Spinning it within a reasonably large (80mm) gap feels a little less of a buttck clencher, so there may be a lot to be said for this approach.

Uwe's solution was one of these Wenglor "laser fork" sensors.

It's pretty straightforward - once the beam is interrupted, the output goes high. The power supply voltage is 10 - 30V, ie compatible with the 24V used by Acorn's inputs. There is a slight compatibility issue, namely that the Acorn expects a tool setter to be normally low (normally closed to ground), going open circuit (pulled high by Acorn's input) when an interruption is seen.

Got a couple of these from German ebay, with 30mm and 80mm widths.

My machine is already set up for the TS27R and I'm loath to change the setup radically at this stage. I'd like the additional radius offset measurement features of the new CHIPS release, so perhaps I can configure the fork to work in the same way, so that I can simply swap them over as required.

Uwe's solution is to fit a standalone Chinesium "PNP to NPN converter". This is an opto isolator with a normally closed / low output that goes open circuit when presented with a high signal at its input. That's a bit of a PITA, so perhaps I can do something different and possibly even better.

NP to NPN converter:

What's needed is a normally on NPN transistor that is turned off when the laser fork output goes high. That requires 2 switches that could be either NPN or N channel. I have a bag of ZTX451 transistors that should do the trick. These are from Diodes Inc, which used to be Zetex (and before that, Ferranti), with a 60V rating and a decent current gain.

I'm going to make a "rat's nest" assembly, rather than fuck about with strip boards or even PCBs. Here's the guts of it:

This will sit inside the control cabinet at the end of a shielded flex cable.

At the other end, I've grafted a Chinesium connector that mates with the laser fork. This seems to be a common connector that I've not encountered before, called an "M8" connector, due to having an M8 x 1mm thread. This one's a 3 way version. Of course, the colours are all to cock. I figured out that the ground connection is yellow, the +10-30V is red and the output is black. I will correct that by the time the wiring emerges in the control cabinet.

With some heatshrink to protect each wire and a piece of adhesive lined heatshrink over the whole thing, it should hopefully be fluid proof like the IP67 sensor itself.

As the rat's nest isn't going to be very robust against shorting itself out internally, some rapid setting epoxy adhesive should do the trick. Obvs I tested that it worked before slathering this stuff on, as it's a one time event. If it doesn't work under the epoxy, I will have to start all over again:

And here it is finally, with the smaller (30mm) fork for testing. The final installation will use the 80mm fork.

Does it work, Fatty?

Yes it does - TFFT. Next steps will be to configure the tool setting function in CHIPs. I've got CNC12 5.4 working after the big update but CHIPS wanted a configuration setup focused on its own features, which I chose to leave until later.

First, I'll check that the TS27R works as expected, then fit an additional cable gland on the control cabinet for the laser fork. That will be the next workshop session...