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Hello everyone, I'm curious to know whether you zero your Z axis to the table or top of the material you're milling and why? I've been setting my cam program and machine to the top of the material from the start, but I believe that I can benefit from changing that to the table spoil board. I've skimmed into my table because of inconsistent sized boards that cause my Mill to take 20 thou's off the spoil bd. If I set my z to the table top using a touch probe and script , then add an additional operation to face the top of the material before milling it I believe I would have more consistent results. I have a Z touch probe coming in the mail so I'm glad to get that added to the mill. I'm using Mach3 and Vetric's Cut2D and Cut3d. I greatly appreciate all advice, Vince

As a long time machinist and programmer, I can tell you definitively - depends on the job. There is no hard and fast rule.

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"Act your age, not your shoe size" - Prince

Chris is correct.
Examples:
1. When surfacing a part to a specific thickness, or when machining a fretboard, you should definitely use the top of your fixture.
2. If you're cutting a pocket in something to a specific depth, then you need to go from the top of the part for more consistent results.

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What Chis and Don said.

You just have to think about what you are trying to accomplish and where the critical dimension / tolerance is that you are striving to achieve.

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Allen R. McFarlen
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+3 when we machine pickguards we zero off the part for the screw holes and countersinks and then zero off the fixture to machine the edge chamfer

PERFECT EXAMPLE.

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"Act your age, not your shoe size" - Prince

Every job I do is zero'd different, so I'd tend to agree with the previous posts.

Thanks to everyone for your replies, I can see why you would do it each way with the examples you mentioned. Very very helpful. regards, Vinny

It's really just a matter of determining what matters and what doesn't matter with regard to precision. Your machine doesn't care where its zeroed at...it's your preference.

I usually (not always) use the bottom of the tooling jig or jaws for everything because, with a tool changer, I can set up the whole job so I just run the first first op, flip the part over, and run the second op, and so on until it's done.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I zero off the spoil board. I don't have to change it so zero is always the same unless I have to re-surface the spoil board. Forgetting to set a new 0 when changing jobs can lead to some scary tool plunges. Ask me how I know.

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I like to zero on top of the part when I can. But when I need to thickness the part it has to be the spoilboard. The reason I like the top of the part is because then I can "go to Zero" where I have marked so I can see if I have missed steps or something has gone wrong. If you go to zero and your z is below the part it is a disaster with the bit routing through your part.

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Ken

oops dp

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Ken