CMM

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Description[edit]

The Coordinate Measuring Machine (CMM) is located in the back-right corner upon entering the Metrology Lab. It is used to measure parts accurately for inspection and reverse engineering.

Principle Uses[edit]

The CMM excels at precision measurement and geometries that would be otherwise difficult to measure:

  • Center and diameter of large holes
  • Center and radius of curvature
  • Flatness/Straightness
  • Orthogonally/angles between planes

Principles of operation[edit]

The CMM uses high-precision encoders and air-bearings to allow tracking the position of a measurement head in 3D. Combined with a computer it can interpret the RAW XYZ coordinates to calculate distances and complex geometries. Our machine is manually moved by an operator, but more complex computer driven models exist and are used in many industries.


Tutorial[edit]

Image Step
Cmm1.jpg

Turn on both the computer and the monitor

(Located to the right of the CMM)

Cmm2.jpg

Open Air-valve: (Located to the right of the computer)

Note: A soft hiss can be heard from the air bearings once valve is open

Cmm3.jpg

Verify correct air-pressure. (Gauge located under the left edge of the CMM table).

If the valve is all the way open it should read about 55 psi. If it does not, stop and notify the shop manager that the air is not at full pressure.

CAUTION: Insufficient pressure will prevent air-bearings from functioning correctly and may damage the machine

Cmm4.jpg

Unlock the X,Y, & Z axes.

CAUTION:  

Moving the machine while locked (while difficult) will damage the rails.


Cmm5.jpg

Begin homing process following onscreen prompts:

Note: The enter/return key, light-pen/stylus, or controller can be used as needed

Cmm6.jpg

XY home position:

Note: If unlocked, it should move easily

Home position is Fully Left (X), Fully Towards the operator (Y), and with the head all the way up (Z). Hold it in position and press ‘DONE’ on the computer.


CAUTION: Do not impact the end stops at high velocity. This will result in a failed calibration and possibly damage

Cmm7.jpg

Z home position:

Cup the qualification sphere using the hole in the Z-rail (as shown). Hold it against the sphere and press ‘DONE’ on the computer.

Cmm8.jpg

Insert the desired probe into hole on Z-head and tighten using locking lever

Note: A spherical tip will work well for most geometry.

Note: An electronic auto-detecting head is available for checkout (Link to the Renishaw instructions)


Cmm9.jpg

Adjust the counterbalance on the z-axis to keep the Z-axis from drifting downward: Adjust the knob on the z-rail, carefully letting go of the probe head to see if it hold. Note: The further down the probe head goes, the more counterbalance is needed.

CAUTION: Failure to adjust counterbalance AND carefully attend to the Z-axis can result in unintentional impacts with the table and machine damage

Cmm10.jpg

Qualify/Calibrate tip: Select single tip probe calibration. Verify tip geometry (sphere) then take at least 4 measurements against the qualification sphere Note: On power-up the computer will automatically jump to calibrating the same geometry it last used following XYZ homing.

Note: Additional points taken on the same surface will be averaged.

Note: After qualification the computer will display the calculated geometry of the probe. Ensure valid calibration using a micrometer and repeat if needed.

Cmm11.jpg

Secure part to table: Using the fixturing points firmly secure part in place. Your part needs to be tight enough that it does not move when you take measurements. Note: Consider the measurements desired, part datum, probe clearance and approach angles when fixturing the part.

Cmm12.jpg

Pick unit system and basic settings: Inches/mm Note: There is no printer so it should be turned off to avoid warning prompts


Cmm13.jpg

Alignment: If desired create a part alignment using one of the alignment methods using the on-screen prompts. Note: Measurements taken using machine “home” coordinates can be confusing due to rotated parts/reference frames.


Cmm14.jpg

Measurement/Features: Select the desired measurement process/type from the features menu. Note: 2D features will be projected to a plane (typically XY).

Note: Verify correct direction of measurement (inside/outside radius) to ensure probe radius is correctly added or subtracted.


Cmm15.jpg

Shutdown: When you are done with the CMM, remove the probe from the z-rail, move the CMM to near the home position, lock the axes, turn off the air and computer. Note: The qualifying sphere should be the only thing on the CMM table when you leave the area.

CAUTION: Failure to lock and secure the Z-axis before closing the air-valve can result in the axis free-falling into the table resulting in damage