Z axis calibration

[ianto36]

Hi all
This might sound daft but how do you set the z axis for depth? I'm afraid of the tool cutting in too low.
If you position the router at the corner of the workpiece to be milled and set this as the z zero are all points calculated in relation to this?
How do you manage if you have to change tools and they are different lengths?
So many questions
Ian

[den73160]

If you position the router at the corner of the workpiece to be milled and set this as the z zero are all points calculated in relation to this?

Yes, that would set the x,y,z to that point on the material to 0,0,0 and unless something happens would be the point where it returns HOME.


How do you manage if you have to change tools and they are different lengths?

This is always the thing that messes up most people. Unless you have a zero plate or an automatic tool changer everytime you change bits you will have to rezero the bit to the material.

[lockeyone]

I place a slip of paper between bit and material and just bring the bit down till it tickles the piece of paper. Sometimes if the bits are the same length and depending on material I will leave the bit loose and run Z to the zero letting the bit set itself on the material. Make sure the bits the same length as the last one. If your afraid to damage the surface you could use something as a spacer and do the same thing and then offset Z the thickness of the spacer. The slip of paper is my most used method.

[Rusty]

Ian:
I use Mach3 as my cnc controller software. You set your starting cutter position (center or wherever you pick) & set the "X" & "Y" axis to ZERO. Select & install the cutting tool, lower the "Z" down to the surface you want to reference as your starting point, then set the "Z" to ZERO. You are now ready to cut the file. I always lift up the "Z" a bit, just in case. Your "Z" readout has now changed reflecting how much you moved it. No worries, the "Z" still knows where the zero is (don't reset any of the axis). When that file finishes cutting your tool will move back to "X" zero, "Y" zero, & "Z" will be what ever you had set for safe retracted height (not sure if that is the right terminology) to be, it should not be zero. If you next file uses the same tool, then you do not change any settings unless that specific file is referencing a different starting height.
If you need to change tools, for the next file, then just lower the "Z" down (after tool is installed) to the starting height & reset ONLY the "Z" axis to ZERO. Ready to go. You can do as many tool changes as required, just remember to reset the "Z" axis to zero each time.
I was scared at first, but it didn't take long to understand what needed to be done. Just remember that the cnc controller software does & goes wherever it is instructed, so most of the booboos are from the operator. Just take to time to go thru the setup carefully before you press the start/go/run button.
Hope that helped a bit.
Good luck.
Rusty

[TReischl]

I stopped at a metal supply house and bought a short length of .5 inch aluminum bar stock. Cut it to about 3 inch lengths and use those for spacers. As all the guys mentioned above, I use it for a spacer. Once the tool "touches" the bar, I set my Z to .5 and presto, I am ready to go. In Mach, it is just a matter of typing .5 into the Z axis display and pressing enter.

I use the .5 bars because they allow me some room for error when I first rapid down. I use the aluminum because it is easy on the cutters.

One thing to remember, especially on home built machines is to always approach the setting height from the same direction. This takes care of any backlash that might be in the z axis screw.

I also do some editing of the cnc file, I take out the first and last move to X0.000Y0.000 and also remove the Z approach height on the first positioning move. My vcarve always sets about .23 something or other and I would rather it NOT be coming down as it approaches. I think I can change that somwhere in the files, maybe I will go look for that! I take out those moves to X0Y0 because I get tired of waiting for the machine while it drives around.

[CRFultz]

Some tooling also has depth rings set at a predetermined height...therefore one set of the Z leaves any more changes at the same height irregardless where your axis may be located for the tool change...
This also helps when your previous Z zero surface has been removed from earlier cuts...


Chuck

[GroBru]

Use a small angle to set your cutting bit one end of the angle buts under the router and the other end supports the bit and you tighten your bit in place
and then you set your 0 z surface if you need to change bit use the angle again and you bits are always the same height if you need a pict i will post
one

[TReischl]

Not quite sure of your method, a pic would be a big help, thanks for offering!

[GroBru]

Here are the picts hope it come out ok and its always comes out the same height the angle in 2 x 1 x 1" wide or whatever you need

[Peteg]

I tried this method when I was changing tools, but found it to not be precise enough (my sloppy work though) So I tied into my emergency stop circuit. I attach a probe to the cutter and a another to a 0.0015" feeler gauge. I lower the Z axis and as soon as they touch, the circuit is made and the machine instantly stops. Then all that is required is to zero the Z axis in Mach 3.

Cheers

Peter

[TReischl]

This is a very old thread, about 13 years worth of old. I have long since put a touch plate on my machine. In fact, I built an entirely new machine during those years.

[Xxray]

Wow, I think this is the oldest thread resurrection I have ever seen but no matter, topic still relevant.

I used a touch plate for years until I started to use drag bits, which do not work with touch plates. So I went the paper method and never looked back, use it for everything now and sold my touch plate as it was just collecting dust. For me, zeroing with paper is just as accurate if nor more, just as easy and considerably quicker.