Rotary Chucks Require Special Procedures
The rotation of rotary chucks in service requires the use of brushes and contact rings at the center of the chuck to bring the electrical current to the coils. If your problem is with a rotary chuck, first check the external connections and controls, according to the test steps listed in the charts included herein. If these tests show that proper voltage is reaching the input leads to the chuck, further tests must be made at the brush and collector ring assembly. Access to this assembly in Blanchard rotary chucks is on the underside, so that the chuck must be removed from the machine. On Magna-Lock USA chucks, access is through a cover plate on the top side of the chuck.
In either case, remove the cover plate and examine the brushes for dirt and wear. Each spring-loaded brush should move freely in the brush holder and contact the ring firmly. Replacement kits for worn brushes are available from Obsidian Manufacturing Industries, Inc. If the brass collector rings are dirty, pitted or discolored, they should be cleaned and polished or it should be replaced.
In rotary chucks, the electrical resistance test for circuits continuity are made at the collector rings. First remove the brushes or block them from contact with the collector ring by inserting an insulating spacer between the brush and the ring. Using an ohmmeter, test the resistance from each ring to ground. The reading should exceed 100,000 ohms. To test for circuit continuity, check the resistance reading across the two rings. The resistance should not differ by more than 10% from the standard value, which is available from any service technician at Obsidian Manufacturing Industries, Inc. If the resistance readings indicate an open, shorted or grounded coil, the chuck will require a factory repair.
When replacing the cover plate on Magna-Lock USA chucks, use a new gasket to assure a good closure against moisture penetration.