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.
|Company / machine model||Chevalier Machinery Inc./ FM-3VS||Ganesh Machinery/ GMV-2 CNC||Hardinge Inc./Bridgeport Series I Standard|
|Table size and travel||9 in. by 48 in., 12 in. by 30-in. Y and X travels||9 in. by 49 in., 12 in. by 32-in. Y and X travels||9 in. by 48 in., 12 in. by 36-in. Y and X travels|
|Head||Manual variable speed, 50-3,750 rpm or 60-4,500 rpm, 3 hp||Manual variable speed, 3 hp||Manual variable speed, 500-4,200 rpm, 3 hp.|
|Ways||Hardened and ground dovetail and square available for table, saddle and column||Hardened and ground dovetail ways, table surfaces and T-slots||Dovetail, hard chrome plated and hand scraped|
|Other features||Acu-Rite, Anilam and Sony DROs, servo power feeds for X, Y and W (knee feed) axes, Class 7 angular contact spindle bearings for runout within 0.00015 in., and double nut lead screws for reduced backlash.||Fafnir spindle bearings, dual spindle-motor fans (top and bottom), spring-loaded way covers, Newall or Fagor DROs, 2-axis Anilam or Fagor CNC package, RS-232 port, halogen light, and built-in leveling pads.||Anti-friction bearings throughout, optional 2-axis DRO and power drawbar, airflow motor cooling system (no fans), optional Acu-Rite MillPwr CNC, and standard quill power feed.|
|Company / machine model||Republic-Lagun Machine Tool Co./FTV-2||Sharp Industries Inc/ TMV||Southwestern Industries/ Trak KE|
|Table size and travel||10 in. by 57 in., 16 in. by 38-in. Y and X travels||10 in. by 50 in., 16.3 in. by 35-in. Y and X travels||10 in. by 50 in., 15.5 in. by 31-in. Y and X travels|
|Head||Manual variable speed, 55-4,250 rpm, 3 hp||Manual variable speed, 60-4,500 rpm, 3 hp||Variable speed, 70-4,200 rpm, 3 hp|
|Ways||Hardened and ground dovetail and square combination||Hardened and ground square on column and saddle||Hardened and ground dovetail|
|Other features||Optional electronic variable speed head and power drawbar, built-in powered variable-speed knees, X, Y and Z servo driven variable power feeds, available CNC package, optional 2, 3 and 4-axis Anilam, Newall and Sony DROs, and available Lagun geared power feeds.||Available axis feed packages and DROs, optional digital variable speed head, double-nut backlash-eliminating lead screws, dual headcooling fans, and CNC retrofit packages from Acu-Rite, Fagor or Southwestern Industries.||Two-axis ProtoTrak EMX CNC and threeaxis DRO system (with part graphics, program storage, canned cycles and math help), precision ballscrews (table and saddle), both CNC and manual machine operation, and optional knee power feed and power drawbar.|