Shops often purchase manual knee mills for prototype, toolroom or onesy-twoesy work. And, a lot of knee mills find their way into training programs.
However, besides digital readout and axis power feed packages, most knee mill builders offer stepped-up versions of the machine that have CNC capability or the option for both manual and CNC operation.
Prices for knee mills range from approximately $3,500 to $12,000, and while CNC on a knee mill adds to its cost, shops may want to consider the option. The increase in productivity that CNC provides makes the extra investment extremely cost effective. Plus, most knee mill CNCs are easy to learn and use.
For the most part, the basic knee mill design doesn’t vary too much from builder to builder. Table lengths may differ, as do machine heads and way types.
Knee mill heads are either step pulley, manual variable speed or electronic variable speed. To change spindle speeds on a step pulley head, operators stop the machine and manually switch its V-belt positions from one pulley to another.
There’s no belt changing in manual variable speed heads. Operators simply crank a handwheel as the spindle turns, which moves two opposing angled plates within the head closer together or further apart to change speeds. Electronic variable speed heads operate the same as manual variable speed heads, except there’s no handwheel cranking.
Knee mill way styles include box/square, dovetail, or a combination of both. Their surfaces are either hardened and ground or chromed. To move machine tables, builders will use either Acme leadscrews or ballscrews. Ballscrews are practically a must for a CNC knee mill.
