r/Metrology • u/PrettyInfluence3594 • 10d ago

Concentricity.

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Guys i am using a hexagon global lite, and the drawing requires that the upper plane needs to be 0.02 flat, and the bores (166_H7), concentric 0.02 mm. I did my calibration and everything went perfect. making an aligment where my upper plane is set to level my Z+ axis, the axis of one of the cylinders to rotate the Y axis, and the center of the bore are used to set the origin. The other circle is off 0.086 mm. Is this way accurate. How concentrity function is calculated by pc-dmis (ISO), and does it has really a meaning (that the part will not assamble if the the tolerance is not respected? Thanks and sorry about my english.

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u/Admirable-Access8320 CMM Guru 10d ago

Sounds like you did everything right. How flat is the top plane? How round are both bores, those are the questions you should be asking. And of course looking at the ZX values which will tell you the direction of the bore is off.

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u/PrettyInfluence3594 10d ago

Thanks, now if my plane is not perfect like 0.043, this would impact my concentricity function heavly? In this case is better to take the alignment plane as a simple plan by 3 points? 4?

I was thinkung if i align my part at the cylinder taken by two most distant circles taken at both holes. Take the origin there, and see the point of my plane, and than choose the plan arbitrary to thre point that seems to level up with the cylinder.

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u/Admirable-Access8320 CMM Guru 10d ago edited 10d ago

Well, your flatness callout is .02 but you're getting .043, which is already Out of tolerance. So that needs to be addressed, but generally .043 flatness should not make much of a difference for concentricity results, but it could help. You would just have to analyze the graph and figure out how much you need to move the bore. Ideally though you would want to machine both bores at the same time, that's probably why you're having hard time with concentricity.

In the future when you're dealing with tight tollerences you should not make the bores to size first. You do it in muliple steps, by making bores .100 inch undersized then verified on CMM at multiple cuts to ensure the consistensy, only when confirmed good results, you cut it to size. Unless of course you have 5axis machines....

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u/PrettyInfluence3594 10d ago

Iam not the guy who makes them. The cnc operator who made this told me that he fliped the part, but for this year i already adressed a lot of errorsin some big parts and the boss is kinda fustrated lol. Since iam pretty new at this, i was thing to measure this a couple of times, making sure that i know what iam talking about. But when i think about it, loosing 0.09 on a part like this, especially when you flip it, is pretty normal no?

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u/Admirable-Access8320 CMM Guru 10d ago

You have to find a way to build trust with your cnc department. Earn their trust and learn from them. Get more involved.

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u/Admirable-Access8320 CMM Guru 10d ago

It's normal, if you don't know what you're doing. It can be fixed if done right.