Knee milling machines

Knee milling machines are versatile, manual-to-semi-automated vertical milling tools characterized by an adjustable worktable supported by a vertical sliding knee casting.

A knee mill supports the work table on an adjustable vertical knee that moves up and down on a column, whereas a bed mill features a fixed-height table mounted directly to a heavy bed casting, allowing it to handle much heavier workpieces with greater rigidity.

"Bridgeport-style" refers to a universal vertical milling machine design featuring a swiveling turret, a sliding ram, and a knee that moves vertically, pioneered by the Bridgeport Machines company and adopted as the universal standard for manual machine shops.

Versatility: The adjustable vertical knee allows you to move the workpiece up and down to accommodate vastly different part heights and complex multi-step machining operations (drilling, boring, slotting, and milling). Manual Precision and Control: Direct handwheel feedback gives machinists exceptional tactile feel for one-off parts, prototyping, and toolroom repairs. Rigidity and Value: Traditional vertical knee mills offer an exceptionally rigid Meehanite cast-iron structure at a fraction of the cost of a full CNC machining center, making them a staple in every professional repair shop.

Maintaining a knee mill involves lubricating all sliding surfaces, ways, leadscrews, and the quill daily using a centralized oil pump or manual oiler, checking the spindle and power feed gearboxes regularly, keeping the table clean of metal chips and abrasive swarf, and periodically adjusting gibs to eliminate table slop or backlash.

The main limitations of a knee mill are lower rigidity compared to a bed mill (making it less ideal for extremely heavy stock removal), a smaller practical work envelope, and manual operation that limits repeatability for high-volume production compared to a CNC machining center.