Another Look at Precision Grinding

By incorporating a precision collet in the Swiss machine’s live toolholder, along with new bearings, the company can produce as many as 30,000 parts with a single grinding wheel.

Often a little ingenuity on the shop floor leads to the most efficient solution. One shop owner developed an effective approach to delivering a burr-free, tight-tolerance part.

In December 2012, Production Machining featured Jeff Bonner, a small shop owner in Naples, Fla. who designed a grinding wheel with a 10-mm shank and 30-mm head to run on his Swiss machines to meet tough finish specifications (see “Grinding on a Swiss”). Here are the advantages Mr. Bonner views for grinding the parts on a Swiss rather than milling them:

• Grinding is a continuous cutting process, which can provide a better finish than milling’s interrupted cutting process, which induces vibration into the part being machined.
• Grinding processes operate at a much higher sfpm than milling. This higher sfpm allows the continuous cutting action to be performed at a higher feed rate while still producing a fine finish. Higher feed rates equal shorter production cycles and increased productivity.
• Milling cutters operate at a potentially undesirable distance from the face of the guide bushing. The grinding wheel operates at the face of the guide bushing in line with the front turning tool, which is typically about 1 mm from the guide bushing face. Operating this close to the guide bushing eliminates the need for a support common to some milling operations. This method produces a part with minimal taper and excellent size control.
• The tool never needs to be dressed and runs until failure, at which time the tool is simply replaced. Because the grinding wheel does not wear as the tool is being used, none of the grinding abrasive gets into the coolant system.
• This grinding process does not produce undesirable burrs on the part, which is particularly important on parts that have overlapping features. A typical example would be an OD thread with a flat machined on the top of the thread. If a milling cutter is used to mill the flat, the burr will go down into the thread and require a deburring operation. The grinding operation produces the flat feature with no burrs pushed into the thread. The part is produced in a shorter amount of time with no secondary operations to remove the burr.