Best way to maintain Z axis setting when changing bits?

[RGG_574]

What's the best way to maintain the Z axis setting when changing bits? Is it possible? Haven't tried it yet, but I want to do something requiring multiple bits and can't quite see how to do this.

TIA,
Richard

[Todd D]

you reset Z axis only after each bit change, best from the same place every time,

[SteveNelson46]

When you change bits the length of the bit that extends from the collet will be different than the previous bit. Resetting z-zero tells the machine where the tip of the bit is. There are some machines that have a built in process that will do it automatically. Others, like those with tool changers, are pre-measured when they are installed in the changer.

[RGG_574]

Thanks guys. That's pretty much what I figured, but was hoping I was wrong. Sometimes setting that Z axis seems a bit hit or miss. Any tips on the BEST way to do so?

Thanks much,
Richard

[Adrian]

How are you doing z-zero setting at the moment? By eye? Feeler gauges? Touch off plate? Something else?

I use a fixed touch off point which is very easy and 100% repeatable.

Any method that is hit or miss isn't fit for purpose and you need to find a new one.

[4DThinker]

I use a scrap of thin paper to put between the surface and the bit. Jog down close, then set your control software to step mode with steps set at .005" or smaller. Step down, jiggling the paper scrap until the bit traps the paper against the surface. Back up one step, remove paper, jog down one step and set that axis as zero in your control software. Paper is usually 0.0025 or 0.005" thick. You'll be within .005" of accuracy every time.
4D

[Burnside]

For repeatable height, my CNC has a tool height sensor, so I measure first tool, set zero and then touchoff the height sensor thereafter for tool changes. Something manual of known height would work just as well.

For most accurate setup of Z0, I use a zero gauge from Mitutoyo (950-111). Generally I just use a gauge block that is 1" tall or paper that is 0.004. If I zero off the paper, I just slide the paper and job down until it sticks, then manual down 0.001" x 4 and set z. Works fine every time. I find the "z" plates you see on a lot of hobby CNCs unnecessary and more trouble than they're worth and slow. I also zero off the bed 95% of the time.

[RGG_574]

I'm doing it with paper. But the Z+ & Z- controls move the axis in fairly gross increments which makes it hard for me to feel like I get it right every time.

I have a Shark 500 and wasn't aware of a step mode. That sounds pretty good so I'll look into that.

I also like the idea of a feeler gauge and may even have some left over from my automotive days. (which REALLY dates me!).

Thanks everyone.

[Burnside]

I am not familiar with your specific CNC, but ones I've used have two movement modes. Jog and transit (rapid move). The jog moves the spindle in exact increments, usually 1", 0.1", 0.01" and 0.001" while transit/rapid move has high/med/low and just indicates speed but distance is somewhat unpredictable.

Worst case you can manually move G0 X+0.004 or G0 X-0.004 in your gcode window but I'm sure your CNC has the two aforementioned modes.

[Vlad]

There is another way I use sometimes.
Measure the distance ( depends if you use the bed or the surface) to the bottom of the bit with Height Gage and plug the number in to mach3/4 Z .

[FabLab Wageningen]

Another paper user here.

Our machine has a Z-axis minimum step of 0.05mm - good enough. Of course, I better use the electromechanic touch plate, but for most use cases, it does not matter too much.

Marcel.