Established in 1952		Page: 1630
		Technical Data Sheet CMM-2

A Rugged Stand for Ball Bar (Dumbbell) Evaluation of Coordinate Measuring Machines

per ANSI / ASME B89.4.1-1997

Stands are pictured with Ball Bars, priced separately

A Ball Bar (Dumbbell) consists of two very round, exactly-matched spheres which are attached to opposite ends of a rather long rigid bar. The exact center to center distance between the two spheres remains constant, while the Ball Bar (Dumbbell) is measured in various positions throughout the X-Y-Z envelope of the Coordinate Measuring Machine. Using this inexpensive tool, an entire C.M.M. system can be quickly and accurately evaluated. Many companies use C.M.M. evaluation procedures which are based on the Free Standing Ball Bar (Dumbbell). With this technique, the center of the Ball Bar (Dumbbell) is clamped to a vertical post or stand.

The advantages of this method include the fact that it is very simple. More data points are collected because the positions of both balls are measured with each move of the Ball Bar (Dumbbell) and that very acute to vertical angles of the bar can be achieved so that a very complete pattern of the machine envelope can be easily explored.

A major error characteristic of the Free Standing Ball Bar is a deflection of the spheres that is caused by the contact force of the measuring probe. Although minor bending of the bar itself is unavoidable, the major source of this deflection has been the bending and twisting of the stand's vertical post. The basis of this problem has been the frail construction of old Ball Bar (Dumbbell) Stands. Most of the present stands in use are adoptions of existing designs previously used to hold indicators. They are not very rugged. By starting with this problem a totally new vertical stand was developed.

This Ball Bar (Dumbbell) Stand, with its robust 2 inch (50.8mm) diameter hard-clad vertical post, with its heavy interference fit into the 25 lb. (11.34 Kg) cast iron base, eliminates the majority of these deflections. The heavy cast-iron base is fitted with three hardened-steel feet which are precision-lapped flat and coplanar to provide a microinch stable reference surface. In addition, this stand is supplied with a hold-down device that consists of a long threaded shaft which extends all the way down through the length of the vertical column and screws into the C.M.M. table, thus removing any tendency of the stand to tip. When ordering, please specify the size and thread count of this hold down so it will fit the threads in the table of your Coordinate Measuring Machine.

The clamping device that is used to hold the Ball Bar (Dumbbell) on the vertical post is machined from two robust blocks of aluminum. The rear block is machined to form a collar that wraps around the full 360° of the vertical post. A slot in this collar is collapsed by a thread to lock the block securely to the post. The front block is fitted with a long Vee Block which is used to securely hold the Ball Bar (Dumbbell). The front block will allow the Ball Bar (Dumbbell) to rotate a full 360° parallel to the vertical post, allowing a full range of positioning. Both of the blocks are hard anodized for wear resistance

The Free Standing Ball Bar (Dumbbell) Stand is available in three standard heights; Part Number FS-14 is 14 inches (355.6 mm), Part Number FS-24 is 24 inches (609.6 mm) and Part Number FS-36 is 36 inches (914.4 mm). Special heights of vertical stands can be custom manufactured. We will give fast delivery from pre-machined components at very reasonable cost. See ANSI/ASME B89.4.1-1997 for Performance Evaluation of Coordinate Measuring Machines.