I have an idea! Please tell me if this has already been done.
If I set a home switch at the XY home location and then allow the Z axis to lower the tool bit down onto the switch (which would be Z home) then load the DRO with the offset of the switch, then no matter what tool I load or how I load it my Z0 would automatically be correct.
I am using Mach3 so I would need to be able to specify that the Z homes last, even better I would be able to specify an XY location for the Z referencing process so that the switch could be on the least used area of my table.
Could this work? Has it already been done and I'm just rubbish with the search feature??
Sure, it can be done. The switch doesn't need to be at the XY home position. It can be anywhere, you just tell the machine to go there. You can include the command to go there in your tool change macro, or add a button on the screen to go there whenever you change tools. You're going to need to know a bit of VB, though.
Mach3 2010 Screenset
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
See "Tool pre-setter" in the CNC Dictionary:
This is a really handy gizmo to have. They're not uncommon on pro CNC machines. You'll want a super sensitive switch so that your tool height is set accurately and repeatably.
I've also seen this done by closing a circuit between the spindle and a block that is insulated from the spindle/rest of the machine.
You can buy pre-setter switches that light with an LED fairly cheaply on eBay. They're pretty accurate and one of those might be just the ticket.
The VB/macros for Mach 3 are out there, already developed by others I do believe. Done right, you'll have a completely automatic way of setting tool heights.
The other approach to the problem is to make sure every cutter has exactly the same offset. Tormach sells tooling that makes this easier.
We all do this on a daily basis in the plasma world. We use a "floating head" that when moved towards Z home trips a switch and the switch offset programmed into Mach so you can find the top of material. Wouldn't work with a router (flaoting head) but I have seen a simple touch plate (piece of aluminum that acts as a switch when the bit contacts it) hooked to do the same thing.
I have a touch plate working in an older version of Mach. This is like the pictures in the links that Switcher provided. The neat thing about a touch plate is that you set it on top of the work piece. The Z automatically lowers until it touches it, raises itself, and then subtracts the thickness of the touch plate in the DRO. This way it will automatically adjust to any thickness of the work piece, and makes router bit changing much easier.
Here is a link when I first wrote it.
Z axis touch plate
Here is a link from Iwill, and some of the problems he had in later versions.
Z axis touch plate
I have not played with it much since. It worked like a charm. I should probably update it or find someone who has already done that.
oh i like that idea, i may have to think about incorporating that into my machine.. once i have one that is...
Grizzly X3, CNC Fusion Ballscrew kit, 3 500oz-in bipolar steppers, 3 203v Gecko's, Linear power supply from Hubbard CNC, Mach 3, BOBcad Pro Art V22, Rhino.