Nonsensical grinding parameters

Dear Doc: I have a 1970s-era, hydraulically driven surface grinder with a unique feed feature. As the table oscillates back and forth, the wheel feeds down at a constant feed rate. It seems this isn’t the most efficient way to grind, and we’re debating whether to modify it to do a rapid infeed at the end of each stroke. What’s your take?

The Doc Replies: I know that type of machine well and have twice recommended to clients to change this feed feature. In both cases, they were able to reduce cycle time without adversely impacting wheel wear or burn.

Courtesy of J. Badger

Figures a and b. Compared to a constant down feed with a maximum DOC of 0.002″ (Figure a), an incremental down feed with a maximum DOC of 0.001″ (Figure b) lowers the grinding temperature and reduces wheel wear while achieving the same cycle time. By increasing the maximum DOC to 0.002″ when grinding at an incremental down feed, a user can cut cycle time in half while experiencing about the same amount of wheel wear and burn risk when grinding at a constant down feed with a maximum DOC of 0.002″.

That’s because with the constant down feed, the DOC increases from near zero at the beginning of the pass to a DOC of, say, 0.002″ (Figure a). In terms of burn and wear, the restricting factor is the DOC at the end of the stroke, or 0.002″.