TOP TEN BORE GRINDING PROBLEMS and how to solve them…TODAY! (part-7)

What’s All the Chatter About?

Those annoying zebra-like stripes that can mar the finish of an otherwise good looking part are called “chatter.” Chatter is usually caused by vibrations that may come from a number of sources.

chatter marks in bore of part

chatter marks in bore of part

First, the chatter may be the result of harmonics in your grinding process. The grinding machine represents a mechanical system of components; machine parts, spindles, bearings, quills, wheels, etc., each with their own natural frequencies of vibration.

Whenever one or more of these components is excited at or near its natural (harmonic) frequency, those components can vibrate violently, and those vibrations can be transferred right into your ground component resulting in chatter marks. You may be able to eliminate this harmonic vibration by changing some parameters in your machine— rotational speed is a good bet. Change the work head speed to spin it faster or slower and often the chatter goes away. If that doesn’t work, try reducing the wheel speed, keeping in mind the wheel may act softer with higher wear.

The next thing to look for is excessive runout in the grinding spindle, quill or wheel. Runout in each of these components can compound on one another, and the cumulative effect at the tip of the wheel can be surprising. Excessive runout can cause vibrations that will result in a chattery surface finish.

However, even if the runout is in spec, you should also check to make sure the grinding system and its components are properly balanced. Most vibrations begin from an imbalance somewhere in the system and can cause chatter. Vibrations from imbalance can also lead to premature wear and failure of spindle bearings and other expensive parts.

Finally, chatter might come from a wheel that is not cutting efficiently. If this is true, try sharpening the wheel with more aggressive dress parameters, using Meister’s Dressing Calculation Tool, which was designed to assist you in setting up the optimal parameters for rotary dressing of vitrified CBN and Diamond grinding wheels. (Click on the link to download it.) Of course, this solution may be robbing Peter to pay Paul, since the more aggressive wheel may eliminate the chatter but produce a surface finish that is too rough. But if this works, you can always adjust the wheel spec on your next Meister order and arrive at the best balance of efficient, chatter-free performance.

About joelcassola

Joel Cassola is a commercial journalist who has written feature articles and case histories for clients in more than 100 trade magazines.
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