Exact definition of X and Y zero

WARNING: My first results for this testing were off because of a poorly drawn grid. See below for the results of the same test done with a grid created using Easel and the X-Carve itself. Post is dated July 13, 2017.

The correct answer is that zero is at the center of your bit.

I had a question about the exact definition of X and Y zero relative to the bit I am using because I want to use my X-Carve to drill precise holes. Is zero at the center of the bit, or one side or the other? So I made myself a test grid and test pattern on Easel.

First try, I zeroed the bit just to the right of the X axis zero on my pattern, and behind the Y axis zero.

The first test came out nearly perfect. I think I am off by just a fraction of a mm on the Y axis, but its close enough to answer the question. X and Y are defined as just to the left and forward of the bit, so the bit is actually already on the grid.

In case anyone was wondering the same thing.

Well that explains it. Here I was thinking I was a loser at measuring things. I had been placing the center of the bit where X and Y meet and my carves kept coming out slightly shifted (it was never a consistent amount but now I see that difference was due to the cutting width of the bit). I just blindly assumed that my bit placement was correct which left me how in the world I could fail at measuring and centering items in a design to only have them come out offset.

Thanks very much for posting this.

X and Y zero is the absolute center of the bit.

Check out @PhilJohnson’s help documentation. He has a ton of videos and this has been covered by him.


Apparently not, based on my test. Otherwise the square I cut would have been shifted to the right and back.

Maybe your machine is out of alignment then? Something must need to be calibrated because the bit’s X/Y Zero is the center of the bit.


Looking at my pictures, maybe the grid I drew is a bit off. I did draw it with pencil. I just put together a 10 X 10 grid on Easel, and I will have the X-Carve cut the grid with a 1/32 bit before doing the test over again. That will have to wait till tomorrow afternoon.

OK, Yea…I’ll go with that but, what confirmed it even more with me - that it is the center of the bit - is when using a zero block. If memory serves (which it does not always do so very well), part of that process is once the bit touches the block you are to take that position and subtract from it the block’s width AND half of the bit’s width. Am I remembering that correctly?

The only zero block I ever got any instructions on using is the Z-probe block, and with that, zero is just the position where it touches the block minus the thickness of the block. I was just using one of the clamp blocks to zero the bit at the zero line of my grid.

I have never used a zero block other than the z probe it comes with but how that would have to work is first, it would have to know your bit diameter, then based off of where it touches on the sides, it will know where the center of the bit is, leading it to know x/y zero. Triquetra has a pretty good demo video (which also shows the bits zeroing to the center of the bit. One thing youll notice is that if the bit is a V bit, they have to use the side of the shaft and not of the V part itself in order to be able to tell where center is.


Yea, that is what I was thinking of. Been awhile since I have seen it so wasn’t quite sure. Thanks!

Are you sure your X and Y axis have the proper steps/mm? You should do that before doing this test.

The X/Y zero is the center of the bit. Any test that shows otherwise probably has something else wrong with the machine.

I just skimmed my wasteboard with a 750 mm square (the size of the grid on the Xcarve wasteboard. I centered my bit on the origin. I cut the square. It cut the grid square exactly. If the true home position was not the center, the square would have been shifted from the origin and it was not.

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I made up a test pattern on Easel and checked the calibration. All my circles, squares, and holes were exactly the right size. If anything was off, it was my hand-drawn test grid. I will try again tomorrow.

All of the comments that tell you that X Y zero is at the center of the bit are absolutely correct. I am the maker of the Triquetra Touch Plate and when you use my system, it sets your work zero at the top of the material for the Z axis and the X and y front left corner. Unless of course you would rather use the right corner, or perhaps any other offset you like. What ever location on the working material you choose to be zero for the X and Y axis is where the center of the bit will be when you tell your machine to go to X and Y Zero. So X and Y zero can actually be located wherever you like but when the spindle goes there, it is the absolute center of the bit that will be positioned above that point.

Charley Thomas
Triquetra CNC


The tip of the bit is always zero, if it has been set up correctly.
But in order to make it simple for us, the post-processor handles the offset that has to be in place for us when milling out stuff.
Lets say you will cut a square that is 50x50mm, you bit is a 4mm bit.
If there where no offset calculated, your square would come out 46x46mm.
That is why you always need correct bit size.
So you will zero your bit relative to the square, typically a corner. And then the g-code generated will be with an offset that is equal to the radius of your bit.
No sure how drilling is handled in easel, but typical it will have no offset. It will therefore drill at the center of the hole, and not take into account the diameter of the bit. if you try to drill a hole that is 8mm with a 4mm bit.
it will drill a 4mm hole at the center.
Dont know if this helped :slight_smile:

Simple…Easel doesn’t support drilling :slight_smile:

X,Y, and Z Zero are all at center of the tip of the bit.

I do a lot of small engraving with tiny V bits or small ended tapers and if it weren’t dead center of the bit my designs would not be centered on the workpiece.

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here is a picture for you visual learners out there.

where the red dot is (the middle of the cross) considered the exact definition of X and Y zero on the bit.

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But is it the center of the red dot, or the side of it? :joy: sorry I had to. Thanks for putting this out there!

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So to make an important distinction for the new folks. Is it true that if you zero a 1/4 inch end mill for x and y that you should not have to re-zero a replacement 1/8 ball nose assuming you have the correct dimensions on the mills measured

Of course you will have to reset the z so that isn’t in the question above


That is correct. To think of it one level higher, X/Y zero is the center of the collet, which in turn will be the center of your bit. This means that no matter what your bit, X/Y zero will always be in the same location relative to the spindle itself.

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