Method for accurate Z zero between tools

[blackhawk]

I know a lot of people (including myself) struggle in keeping an accurate Z zero position between multiple bits. The biggest issue for me is when I am doing 2.5D text in a pocket. Usually, I will have a 1/4" EM doing the pocket clear, then I use a V bit for the letters. I can never seem to get the EM and V bit to cut exactly perfect to get a clean pocket bottom. So, I came up with the idea of using a dial indicator as seen in the picture. I mounted the dial indicator to a linear rail slide to give me smooth and accurate travel. Then I simply hold it in place with a very strong neodymium magnet.

First, I zero to the top of my material with the Z zero plate as normal. After I finish the cut with the first bit, I bring it over to the dial indicator and do an MZ=0 command. Then I slide up the indicator until the dial is set to zero, holding it in place with my magnet. I then move the router over and change bits. Then I move the router back over the dial indicator and slowly jog the router down with the "K" command active, until I get to the zero reading on the dial. Then I do an ZZ=0 command to set the zero point of the new bit. Now, I have an accurate zero point between each bit.

I have only gotten to try this out once on a 2.5D pocket so far, but my first trial worked great. I had a very clean and even bottom in my pocket.

[carlosgmarroquin]

Thanks. I will try this technique for sure.

[michael_schwartz]

Smart and simple.

Another use for this technique could be for zeroing bits when the top of the surface has been machined away. (If you didn't want to zero to the bed)

Using multiple bits within a 3D file could be an example

[dana_swift]

Brad- Thanks for the technique! I switch bits often enough to appreciate the simplicity of the idea.

Not only that, I have a Dial indicator I used for other setup work that I could use to try it.

D

[ATX Poly Products]

Nice little tip! I also have seen a bit of variance when doing a tool change and re-zeroing. Nothing super big but just a hair.

Thanks!

[bleeth]

You could also rig up a fixed position Hex nut with a bolt that had the head machined flat in it and after you zeroed to top the first time move your bit above it and screw the bolt up to touch the bit. Then use it to set the next bit. Or set it at bed height. Or use Gary's (and others) fixed z-zero method with offsets.

[Gary Campbell]

Another method I have used on multiple bit files is:

1) Zero to top of material with bit 1
2) Affix a machinable block out of the cutting area
3) With bit 1 at z zero, machine the top flat
4) Change subsequent bits over the block with z at zero
5) raise and then lower bit to zero to double check

This eliminates rezero to a material that may move due to machining. A loose zero plate and OEM files will give results plus or minus .010. Thats ten thousandths up or down. In worse case scenario, 2 bits could be off as much as .020

[dana_swift]

Being the curious sort that I am, I got to wondering how repeatable is the ZZero routine? So.. I wrote a SBC file to measure it.

In Summary:

1) I found zeroing at the same point and the same bit reliably returns to the same value of ZZero, +/- 0.000" (Almost always, and +/- 0.001" when it wasn't.)

2) Just removing and replacing the ZZero plate could cause a +/- 0.002" variation.

3) Use the K command to select a nearby point to measure on the material surface, then significant variations were seen over +/- 0.010".

This is just a quick look, but I will be paying more attention to it now.

Anybody else wanting to measure their ZZero repeatability is welcome to a copy of my code. In exchange you must publish your experience.

What my routine does is pull up exactly 1.000 inch from the measured material surface without changing the zero value in Z, so if the Z readout reads 1.003" the variation was +0.003". If the Z readout is 0.996" the variation was -0.004". Etc.

[[ Also note the file should be ".sbc" however the forum will not not allow uploading anything but ".sbp". So you are advised to rename it back! ]]

[blackhawk]

I ran a 3D file last night that used 3 bits. Between each tool change I used the zero plate and zzero routine. I then ran the bit over to my indicator to check the accuracy of what you get using the zero plate. One bit was off .004" and the other .001", which is actually pretty good. I placed my zero plate in a different spot everytime, but each spot was probably within a 4 inch circle. My part was pretty flat too, because I had surfaced both sides on the bot beforehand.

[applik]

We have tried all sorts of methods for re-zeroing without much luck. The bolt is the latest method, it comes closer than any other we've used, but still not acceptable when doing the 3D. The Z just will not go back to "dead on". In the second picture, the ridge measures .004 higher on one side than on the other. Sometimes it's lower, never the same outcome. Would be great if it would be exact, but I seriously doubt that will ever happen. Funny thing is, we can get the X and Y right on, but never the Z.

Will be watching this thread with great interest.

SL