Round Peg in a Round Hole

QI wxtnt to change the chuck on

• my drill press, but I'm having a problem identifying the taper size on my drill-press spindle. The old chuck has no markings that relate to spindle taper. Any clues?

David Umpiiress Woodbury, NJ

A A taper is a conical surfacc on

• the end of a shaft or in a hole. One kind of taper is a self-locking taper, which is used as a method of joining mechanical assemblies together, as in fixing a drill chuck to a drill-press spindle, or a lathe center to a lathe head stock. If the tapered parts match, the snug fit locks them together strongly enough to transmit considerable torque. Tapers are easy to disassemble, vet will always line up accurately when reassembled.

Taper connections are so common that several different types of self-locking tapers have been developed — each type representing a family of sizes with their own standardized dimensions. Some of the popular tapers have names such as "Morse Taper," "Jacobs Taper," "American National Standard Taper," and soon.

To identify your taper, measure the drill-press spindle very carefully. Record the larger diameter, the smaller diameter and the distance between them, which is the length of the tapered section. Don't include straight parts of the shaft in the measurements. Match up your measurements with the dimensions of a specific taper listed in tables in machinery text books or catalogs.

Tapered pieces must match exactly. A near match may seem to fit but can wobble dangerously or separate when run up to speed. (See drawing.) To test the fit of a tapered chuck, clean the spindle and socket, then rub a line of chalk down the side of the spindle. Seat the chuck gently on the spindle, and turn it '/■» turn. Remove the chuck, and look at the chalk line. If it's smeared along the full length of the spindle, you have the right taper. If the chalk is not uniformly smeared, you may have the wrong taper. Also, inspect the spindle for burrs, embedded chips or




Sides of taper not Sides of taper fit exactly parallel. exactly along length.


other damage. A couple of careful strokes with a mill file can remedv a

small amount of damage. Otherwise, a local machinist can true up the taper for you.

Fred Mat lack Director, Rodalc Press Design Group

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