Determining Centerline with Straddle Holders

With an axial feed holder coming from the turret, the wheels should already be close to the centerline unless the holder is defective.

When using a straddle type holder which comes in from the cross-slide, or x-axis of a cnc machine, the following procedure should enable you to locate the opposing knurling wheels above and below the exact centerline. This is normally preferred to keep spindle forces to a minimum on your machine.

  1. After setting the holder with the proper opening (at the minor diameter), back it off slightly.
  2. Use any flat strip of metal or hard plastic and just touch the two knurling wheels to this strip and the strip to the workpiece blank diameter at the same time.
  3. Now remove the strip and advance the holder by the radius of the knurling wheels (1/2 the diameter of the wheels) + the thickness of the strip used + the radius of the workpiece (1/2 the blank diameter). Now the wheels in the holder will be very close to the centerline.