# Translating and Rotating Rules when programming or measuring with a CMM

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#### Mr. Friend

Hi friends,

I'm interested in obtaining a list of rules concerning translating and rotating when programming or measuring with a cmm. I know that problems can occur if one rotates the wrong angle during a compound angle measurement. What would be the order of precedence? A list of rules would really help me avoid erroneous measurements.

Any help would be greatly appreciated.

#### Michael_M

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I am attaching a reference that has been hanging on my wall since before I started here. It is used for sine plates/compound angle compensation. It may or may not help.

For the CMM, you have your 6 restrained features (X-Y, Y-Z, Z-X, X, Y, Z). As you rotate or move the CMM resets itself to these constraints.

For example, you take a top plane that is 5 degrees in the real world. If you use this feature to set Y-Z and Z-X, the machine calculates everything as if this is 0 degrees.

The 'alignment' (by my machines terminology) is X-Y. If you rotate this, the rotation happens at X0, Y0, and Z0 as constrained by Y-Z and Z-X).

Where this gets confusing is when you are looking at the 'origin point'. Take rotating a line, the rotation is different if your origin is at point 1, 2, 3, or 4.

1.........2.......3.................4
--------------------------------

Translating follows the same general principle, it is constrained by the same 6 features but you are 'moving' X, Y, or Z. On the CMM I used, if you translate an angled surface, it moves 90 degrees along the constrained feature (X, Y, or Z), and I cannot recall if this is common among the other CMM's I have used. In other words, if you have a 45 degree line and translate it Z+, the CMM I use moves the line 'up' by the amount of translation (it does not move it up and out for example unless I say to translate it Z and (X or Y).

Compound angles are a bit more difficult and I have only programmed 2 or 3 of them so I am working from limited knowledge. However, what I do remember is you have to be very careful to rotate and translate from the exact 6 restrained positions you want before doing the second angle.

I hope what I have written will help.

#### Attachments

• CCI12052014.pdf
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#### Mr. Friend

Thank you for your response Michael. I'm strong in basic alignments, or 3-2-1 alignments (level to plane, rotate to axis, halt translation, or plane-line-point). My question concerns compound angles and which angle to rotate to first. Using the 3-2-1 given above, for example, say the print requires a rotation of X Axis about Z and a rotation of the Z-plane (primary plane) about X Axis. Which one would come first?

#### Michael_M

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Thank you for your response Michael. I'm strong in basic alignments, or 3-2-1 alignments (level to plane, rotate to axis, halt translation, or plane-line-point). My question concerns compound angles and which angle to rotate to first. Using the 3-2-1 given above, for example, say the print requires a rotation of X Axis about Z and a rotation of the Z-plane (primary plane) about X Axis. Which one would come first?

Is there any control frames that help dictate the rotations. If there is, you would rotate in the primary/secondary/tertiary format.

Other than that, I do not know of any specific rules so I cannot help further.

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#### Mr. Friend

No FCF, Michael. Sorry. I'm thinking that when faced with such a decision, I would rotate within the plane I am in first. So If I have a 3-2-1 alignment, then I would rotate the X-axis about Z (since I leveled to Z), then rotate the Z plane itself.

Thank you for your assistance, Michael. And thank you for your sine plate instruction PDF.

-Mr. Friend