Mechanical Touch Off Tool Recommendation
Here is my question:
What is a good mechanical touch off/home switch tool that I can put between the stage and the tool to use as a home switch that will give me a fixed height within the system every time that does not require conducting through the tool? I need it at least precise to 0.001" or better. What I'm imagining is some small platform that rests on the stage between the tool and stage that has a fixed known height that it triggers/releases the mechanical switch, allowing for fairly rapid and repeatable homing.
Or is there a better way to do this?
I might have missed someone else's post on this, for which I apologize, I wasn't sure what to search for.
Edit: Besides the one I found for $1250.
For the piezo, Assuming this is a home-brew and not something off-the-shelf, you can remove the piezo element from a $2.00 buzzer and use it. For manual touch-off, you can just connect a voltmeter across the element and read the voltage as you jog the tool. For automatic, you will need to have a computer read the voltage. Piezos are extermely sensitive: a tiny deflection will produce a measurable voltage. I suspect you will get reproducability to within 100 nanometers or so. I have used a $2.00 buzzer piezo, a 9-volt-battery, and a junkbox potentiometer to move a morroe in an interferometer, getting about 100nm/volt. The effect is similar for converting displacement to voltage as for converting voltage to displacement.
I made a couple of Z touch off tools last year.
The first is mechanical, an adjustable arm actuating a very sensitive limit switch.
The arm is adjusted so that it is dead level at point of actuation, so that where precisely the tool touches is not important.
The second is electrical, two pieces of aluminium separated by a plastic and epoxy sandwich are connected by the tool touch.
I have found these repeatable to within a couple of hundredths of a millimetre (0.01mm) which is better or at least comparable to your requirements.
Cost me time and bits from scrap bin.
Could easily be changed to trigger signal to LinuxCNC rather than just optical LED
What is a good mechanical touch off/home switch tool that I can put between the stage and the tool to use as a home switch that will give me a fixed height within the system every time that does not require conducting through the tool?.
You could make something like the Renishaw patent devices, with three rods and 6 balls. That has the advantage that you can choose a spring to suit your tool force.
Alternatively, you might be able to use one of the dial-indicator style devices:
Or possibly this
www.ebay.com/itm/150802223742 though that specifies "conductive" so an enquiry might be needed. I have bought a fair bit of stuff from CTC in HongKong.
While I don't know exact forces behind it, the tool itself is robust enough (Assuming you go slow, which is easy enough to do) that it can exert a decent amount of force as long as it isn't being pushed into something hard.
I'm hoping that someone has, for relatively cheap (The only one I found was $1250 from Centroid www.centroidcnc.com/cnc_tool_set.html), a spring loaded switch that always actuates at the same known place and can be connected to EMC to act as the home switch for Z. The company has tried both of the tools listed by andypugh. However, I'm trying to remove the human factor from this, except the need to place the switch and take it away once Z is zeroed, since it would save a bit of time when things get swapped around.
Edit: Another good example of what I am thinking of is for a manual/semi-automatic tool change in a CNC process that I've seen, where the system lowers the tool down to know the length of the tool once the tool is complete, then returns to milling. It just needs to be non-conductive though, which I don't think was the case here.
I think I want to avoid having to actually make something, as I can think of exactly how I would make it, but don't have enough time..
Maybe something like this:
That one appears to have a zirconium plunger and a repeatability of 0.0001mm
There appear to be ruby plunger options.
Not cheap, but all there basically.