Threaded Ball
Made from Hardened Stainless Steel with a Tapped Hole
Threaded Ball
A very sound approach for rigidly holding the spherical components on a Kinematic Platform is to use drilled and threaded balls. The drilled and threaded balls have gained great popularity of late. This surge in popularity is based on the results of some recent kinematic research that indicates that a ball glued into a mating spherical cup is very sturdy, and may even be the best way to mount a ball. The ball is held rigidly in position by a thin glue joint. This design has high shear-resistance, as the ball is buried in the recessed spherical-cavity. It can not torque due to the threaded shank of the holding screw. In addition, it is insensitive to hygroscopy of the glue because there is almost no exposure of the glue line to the atmosphere.
This ball is held in place by a threaded fastener. Because the ball is held from behind with a machine screw, there is no interruption of the spherical surface. This provides a smooth, clean working surface. The Lotus Wrench shown in the Kinematic Components Catalog #105B is an excellent tool for installing these balls from the front. Three of these balls provide a very high quality substitute for a conical cup or trihedral clamp. These balls are an excellent choice for the three spherical contact points in the kinematic system.
Standard drilled and threaded balls are offered in micro-grain 440C stainless steel that is hardened to 58 HRC minimum, or in extremely stiff tungsten carbide (TC) with a Young's Modulus of Elasticity of 98,000,000 PSI and a very high hardness of 91 HRA. TC is the hardest, most rigid material commonly available.
Threaded Ball Specifications
| Part No. |
A-Diameter ± 0.0001" |
E-Thread |
F-Depth Minimum |
| 250-B-T |
0.25"
6.35 mm |
4-40 |
0.150"
3.81 mm |
| 312-B-T |
0.3125"
7.9375 mm |
6-32 |
0.150"
3.81 mm |
| 375-B-T |
0.3750"
9.525 mm |
10-32 |
0.200"
5.08 mm |
| 500-B-T |
0.500"
12.700 mm |
1/4-20 |
0.250"
6.35 mm |
| 625-B-T |
0.625"
12.700 mm |
1/4-20 |
0.250"
6.35 mm |
| 750-B-T |
0.750"
19.05 mm |
1/4-20 |
0.250"
6.35 mm |
| 100-B-T |
1.000"
25.4 mm |
1/4-20 |
0.250"
6.35 mm |
See here for Kinematic Mounting Hardware - Balls prices.