How to Use a Coaxial Indicator

---

Using a Blake Coaxial Indicator for Accurate Machine Setup

The Blake Coaxial Indicator is designed to quickly locate the center of a bore, boss, or cylindrical feature while the machine spindle rotates. Proper setup and operation help improve alignment accuracy and reduce machine setup time.

Step 1: Pre-Position the Workpiece

Move the machine table until the spindle is approximately centered over the bore or outside diameter to be indicated. Initial positioning should place the indicator within its operating travel range.

Step 2: Install the Indicator

Insert the Blake Coaxial Indicator into the machine spindle and attach the restraining arm to prevent the dial face from rotating during operation.

Select the correct feeler:

• Straight feeler for internal diameters
• Curved feeler for external diameters and larger bores

Step 3: Set Proper Contact

Adjust the feeler so it maintains smooth contact with the workpiece surface while allowing the indicator hand to remain near the center of its scale.

Before starting the spindle, verify there is adequate clearance and no interference.

Step 4: Rotate the Spindle

Run the spindle at a low speed, generally not exceeding 700–800 RPM.

As the spindle rotates, observe the indicator hand movement:

• Large movement indicates greater offset
• Reduced movement indicates improved alignment
• No movement indicates the workpiece center is aligned with the spindle axis

Step 5: Adjust the Machine Table

Move the machine table incrementally along each axis until the indicator hand movement is minimized. Repeat adjustments until the dial hand remains stationary during spindle rotation.

Best Practices

For best results:

• Use moderate spindle speeds
• Keep feelers clean and undamaged
• Verify smooth contact throughout rotation
• Avoid excessive pressure against the workpiece
• Store the indicator in its protective case when not in use

Common Applications

Machinists commonly use coaxial indicators for:

• Bore centering
• Fixture setup
• Precision milling alignment
• EDM setup
• Spindle alignment
• Lathe setup operations

 The Blake COAXIAL (co-ax) indicator is primarily as a precision centering instrument for locating a work piece on a horizontal or vertical machine tool while the spindle rotates under power. Learn how to use a Blake coaxial indicator.

The Blake COAXIAL (co-ax) indicator is equally useful for positioning in the situation where it may be desirable to turn the spindle by hand the direction and distance of location error may be determined thus:

DIRECTION is indicated by the radial position of the feeler when the hand is at its high, or low, point of travel.

DISTANCE is indicated by the total travel of the indicator hand thru one full revolution of the machine spindle.

THE FEELERS

• The STRAIGHT FEELER is used for inside diameters to approximately 4.25” inches.
• The CURVED FEELER is used on outside diameters to approximately 4.25” inches and may be used on inside diameters over approximately 1 inch.

SET-UP and HOW TO USE A COAXIAL INDICATOR

1. Pre-position work to within the indicator travel range.
2. Attach restraining are to indicator and ensure there is a suitable stop in place. This will keep the indicator from rotating while spindle is operating so operator can easily and conveniently read the dial.
3. Place appropriate feeler in indicator rocker bracket and secure with thumb-screw. Position rocker bracket on rocker friction joint such that small indicator hand is centrally located on its graduation scale when feeler is in operational contact with work-piece.
4. Start machine spindle. CAUTION: Check for interference before turning on power. Speed should not exceed 700 to 800 rpm at any time.
5. Move machine table along axis of one positioning screw to a point where the indicator hand travel range has diminished to its lowest distance, thus, indicating that the center is centered in the spindle plane in the one direction.
6. Move the machine table along the axis of the other positioning screw until the indicator hand travel range diminishes to zero, thus indicating that the work-piece center is in axial alignment with the machine spindle.

NOTE:     STEPS 5 & 6 will need to be repeated until needle movement reduces to ZERO movement. )The Blake CO-AX (co-axial) indicator is fitted and tested for operation of at least 58° F.  Bearing/bushing stiffness may be present at lower temperatures.

DIAL GRADUTAION is divided such that each division represents .0005 inch of AXIS OFFSET (deviation from true location) when the feeler is tracing a diameter of two inches.  (Varies slightly with feeler angle.)  [Note: Dial graduation is different for 801-E Economy model.]

CARE

Under normal conditions The Blake COAXIAL (co-ax) indicator should require no servicing and only the consideration in use and handling due any precision instrument.  Allowance for familiarization should be made when it is first being used.