We’re pleased to welcome back guest blogger Brian Dechene, GCH Machinery’s technical development director and ID/OD grinding specialist.
While reading a trade magazine last week, I came across an interesting article on shoe-type centerless workholding fixtures for grinding ID and OD surfaces on ball- and roller-bearing rings. Although the article provided a good overview of shoe-type centerless grinding, I’d like to take a deeper look at this important manufacturing operation.
Traditional centerless grinding dates back to the early twentieth century. The design is based on the use of a grinding wheel, a regulating wheel and a work rest to support the part. When set-up correctly, the geometry of how the part touches these three elements will result in a nearly perfectly round part. While there are few limitations on the part material, only the part OD can be ground.
Patents for various magnetically driven, shoe centerless fixtures for OD grinding began to appear in the mid-1940s. The regulating wheel is replaced by a “shoe” that contacts the part and opposes the force from the grinding wheel. A second shoe located near the grinding wheel itself replaces the work rest and provides additional radial support. A driver locates the part axially and the magnetic force rotates the part with the driver. Because the geometry of the shoes is similar to that in traditional centerless grinding, the same nearly perfect OD roundness can be generated. While OD grinding with shoes is limited to one part at a time, the number of OD forms that can be ground is almost limitless.
Designs for magnetically driven, shoe centerless fixtures for ID grinding also use two shoes and a driver to locate the part. The positions of the shoes differ from the OD grinding set-up. For ID grinding, the shoes locate on the OD of the part which has been ground in a previous operation. The tooling layout ensures that the quality of the OD is copied into the ID, and the concentricity of these two surfaces will be almost perfect.
Unlike traditional centerless grinding, magnetically driven shoe centerless grinding requires that the part be made of magnetic steel. One ground face is also required for locating against the driver. OD or ID shoe centerless tooling can handle many complex shapes.
The article I read suggested that the best way to obtain a consistent level of accuracy in the concentricity was to grind the OD and ID in a single set-up. This is when I determined that more information would help the reader.
Small batch grinding of ODs and IDs in a single set-up does have some advantages with some reduction in tooling costs and set-up time. On the other hand, processing a part in this manner generally requires a machine with a much larger capital investment and a much larger footprint. Because of the compromises required in tooling layout, set-up can be challenging. Correct set-up will yield part quality that is consistent with other shoe-type centerless operations.
A different approach to grinding small batches of rings is to grind the OD and ID in different set-ups on the same machine. The machine will first grind the OD of the part. The tooling used is designed to the perfect geometry needed to achieve highly precise roundness and size control. This tooling is also designed for an easy, less-than-one-hour changeover to the ID set-up. The grinder’s CNC control facilitates part programming and stores all programs for future use.
GCH Machinery recently completed a total remanufacture of a Heald 2EF-700 grinder which used this concept for small batch grinding of rings. The tooling was designed around a segmented adjustable magnetic driver and shoe tooling package that allowed for a range of parts from 1” to 18” OD. The CNC control package allowed the operator to grind OD, ID or face in any configuration that could be required in a bearing ring. Set-up times were less than an hour and grinding time was very quick. The design and accuracy of the slides meant that in-process gauges were not required to hold the required tight tolerances.
There are still other approaches to grinding parts using shoe centerless tooling. How do you determine the proper approach for your needs? Contact the grinding experts at GCH Machinery. We offer the machines to grind faces, ODs and IDs. We have case studies demonstrating our experience in ring grinding. From high-volume, small-diameter parts to low-volume, large-diameter parts, we have solutions.
Brian Dechene can be reached at firstname.lastname@example.org.
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