XYZ Zeroing plate and tool diameter

A quick question about the XYZ plate. How do you account for different diameter tools when determining the zero positions for the work piece?


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You tell the program what bit your using and it makes the adjustments that are needed. They have posted some tutorials on how the different programs are used. That would answer some of your questions.


Great, thanks Greg. Good to confirm it adjusts for the bit radius.


You are very welcome.

I’ve been talking to Ron Olson who made a zeroing block and wrote a quick program for the ShopBot at his Makerspace. The local Makerspace here has a similar shop bot so I decided to fire the design off to Xometry ( and get one milled for when a project is too big for the Longmill.

In the course of our discussions, I was pondering the fact that finding zero is helpful, especially for repeatability - but only if you can ensure your workpiece is consistently square to the table. On my Longmill I intend to put a few dog holes in the corners of the waste board with the machine to give me corner L’s to index to every time.

However, even if you have those, it’s easy to knock something out of square when securing it and not notice. Ron latched on to that comment, thought about it, and is going to add code to the calibration stage to address it. The logic goes like this: One the zeroing process is complete the machine now has the ability to know where the exact corners of the block are (since the length of the zeroing block is fixed and the center of the zero point is fixed and known and now mated to the absolute coordinates of the machine). By backing off and touching the side of the zeroing block in the Y axis 3 times, at three different locations, it is possible to determine if the work piece is skewed. This is achieved by checking whether the value from the corresponding axis is changing materially or not - since moving in a straight line along one axis should result in no change in the value on the opposite axis.

For many cuts a small amount of skew is not a huge deal when the piece is cut from a larger blank (although too much skew can cause you to run an expensive bit in to a screw in the “keep out” area unexpectedly). However, if you’re working with outside dimensions of the workpiece that are already cut and accurate (say a sign blank) and you need to maintain square to them, it is quite important to know if you are off square and this quick skew check can provide early warning and insight.


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Your overthinking it. Stop blocks can work fine. Make them big enough and tight enough in the holes there will be no problem knocking them out of alignment. Use brass with a flat side on one face that the parts regester too and there will not be a problem. Even hardwood dowel if its tight enough in the holes will not wear especially if your careful in setting it up properly.

I just got the Fedex notice that the shipping center has my package. I hope to pick it up later today and will post some photos of the unboxing. I guess I need to design a project and head in to the Makerspace while I wait for my Longmill, and test this new calibration block out!

I’m itching to get out in the shop and make something, so this is just a teaser image until I can write up a long post and show the caliper measurements etc. Suffice it to say I’m very impressed and the pieces are perfectly smooth and very accurate! Ask away if you have questions.

If you want to try milling or 3D printing something for your shop or one of your other hobbies, you can still get the USD$50 credit towards your first project by signing up at Xometry here: and feel free to share that link with friends but please don’t abuse it.

By way of comparison, this 3.5"x3.5" x .75" piece of milled aircraft grade aluminum was about USD$32/ea in a qty of 3. I think it was still <$40 if I only ordered one, but I can’t recall for sure. It was affordable enough that I bought one or two more as gifts. :slight_smile:

I’m hoping to try it out later this week, but may be delayed due to Halloween. More soon.


PS - it is dead square as expected.

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