Cam-grinding options
Ask the Grinding Doc Columnist Jeffrey Badger, Ph.D., responds to a question about the difference between "constant rpm" and "constant metal-removal rate" when it comes to…
Dear Doc: I grind cams and have the option of doing “constant rpm” or “constant metal-removal rate.” What’s the difference?
The Doc Replies: Cam grinding is just a funky type of cylindrical grinding, where the shape isn’t a basic circle but sort of an egg shape, which creates special challenges.
In plunge-type cylindrical grinding, the basic equation for specific mrr (smrr) is:
smrr (mm2/sec.) = DOC (mm) × workpiece surface velocity (mm/sec.).
But here’s where it gets tricky. The workpiece surface velocity gets faster as the contact point of the wheel and cam gets farther from the axis of rotation. This changes the equation to:
smrr (mm2/sec.) = DOC (mm) × π × 2 × workpiece radius at contact (mm) × workpiece rpm ÷ 60.
That means surges occur in the smrr, increasing wheel wear and the risk of burn.
As a result, some clever people developed constant-smrr grinding. Here, the workpiece speeds up and slows down within one revolution, keeping the smrr constant and minimizing the surges.
Review the print ads from this magazine to continue
This quick advertiser review unlocks the rest of the article and keeps the full-screen reader focused on the ads instead of the page chrome.
