Lathe Crank Web

This part named “Crank Web” will have some profiling on the OD (Outside Diameter), a #14 drill, and a #31 drill through hole.

To make the part, you are going to analyze the part drawing provided and deduce the fastest approach to machine the part. You can use a CNC program or GO TO option to machine the profile. 

The Specifications for feeds and speeds for manual (GO TO) machining are:

Specifications for CNC program are:

The charts on the tool holder to the left of the lathe has tentative specifications for feed rates and speeds for conventional metals used in the machine shop. Consult an instructor or TA for more specifications.

Now we move on to the process of defining the part contour.

This step resembles an “Etch-A-Sketch” like process of identifying the endpoints of line segments that define our contour.

Note that Z coordinates are negative and X coordinates are given by the diameter of the part.

Fill the table below to define the points that define the contour.

Events/points 1, 7, and 8 are used to define the stock material and hence complete the cycle in the case of CNC program option.

We will utilize the GO TOfunction to machine the part profile.

Order of Operations

Use manual or CNC programming for the following operations. Calibrate tools as specified in the Setting Up Tools  tutorial.

  1. Hold stock in lathe chuck. Face and turn profile.
  2. Chamfer the exposed faces of both diameters to eliminate sharp edges.
  3. Cut off to approximately 0.35” long.
  4. While holding the part in a 1/2” diameter collet, face the large diameter to .188” and machine the last chamfer.
  5. Center drill then drill thru with a #14 drill.
  6. Use the special brass collet in a square collet block to grip on the 1.25” diameter.
  7. Mount the square collet block on 1/16” x 1/2” parallels in vise on the milling machine.
  8. Use the Edge Finder and some Arithmetic to establish the center of the Crank Web.
  9. Move 1/2” off center.
  10. Spot drill then drill thru with a #31 drill.

Your part is done.