Ram-Type Milling Machine

Overview

A ram-type milling machine is a knee mill whose spindle head is carried on a horizontal ram that slides in and out on top of the column. The ram lets the operator push the spindle forward over the front of the table or pull it back, covering a wide work envelope without moving the part. Combined with a head that swivels and tilts, the ram makes this one of the most flexible manual mills built, and it is the configuration most people picture when they think of a Bridgeport style machine. The reach the ram provides is the machine's reason for existing.

The machine is built on the Base & Column, which carries two sets of ways: vertical ways on its face for the Knee & Elevation and horizontal ways on its top for the Sliding Ram. The Tilting Spindle Head hangs off the ram nose, and the work rides a slide stack of knee, saddle, and table.

The sliding ram

The Sliding Ram is what names the machine. A ribbed Ram Casting slides on the column's horizontal ways, driven by a Ram Pinion meshing a Ram Rack through the Ram Handwheel. Pushing the ram forward extends the spindle out over the table edge, which is invaluable when machining the face of a tall fixture or reaching into a large weldment clamped to the table. A Ram Gib takes up wear in the dovetail, and once the ram is positioned a pair of Ram Locks lock it rigid, because any looseness here would show up directly as chatter in the cut.

Tilting spindle head

The Tilting Spindle Head mounts to the ram nose on a graduated Swivel Plate and a Nod Trunnion, so it can swing left and right and tilt fore and aft. Setting the head at an angle lets the operator drill or mill angled holes and faces without tilting the work. A Head Motor turns the spindle through a Variable-Speed Drive, a variable-pitch sheave drive that changes speed steplessly by squeezing a Drive Belt between two cones, so any speed is available without gear shifting.

The Milling Spindle runs in preloaded Ball Bearings inside a Quill, a sliding sleeve fed down by the Quill Feed Mechanism for drilling and boring, with a Micrometer Depth Stop for repeatable depth. The R8 R8 Spindle Taper is self-releasing and a Drawbar clamps the tool into it.

The slide stack

Work motion uses the familiar knee-mill geometry. The Knee & Elevation rides the column ways and is raised on an Elevation Screw to set Z. The Cross Saddle gives cross travel on a Cross-Feed Screw, and the Worktable provides the long X travel with a graduated Table Handwheel at each end. Adjustable Trip Dogs trip the power feed at the ends of travel, and tapered gibs in the knee, saddle, and table keep the slides tight as they wear.

Power feed, lubrication, and readout

A Three-Axis Power Feed can drive all three axes. Each axis has a small Feed Motor and a Feed Clutch, coordinated by a Feed-Rate Control, so the operator can run steady mechanical feeds on table, saddle, or knee for clean finishes. The Lubrication System system meters oil to every slideway and screw on demand. A Control & DRO cabinet houses the motor controls and a DRO Display reading three Glass Linear Scales, so axis position is shown to five microns rather than counted off dials. The Coolant System system floods the cutter and clears chips into the base.

Materials and use

Castings are stress-relieved gray iron, ways are hand-scraped and oil-grooved, and the spindle and ram pinion are hardened alloy steel. The variable-speed sheave faces and the quill are hardened and ground, since both see constant sliding contact, and the head bearings are preloaded to keep the spindle running true. Tapered gibs throughout let a machinist take up wear during a rebuild rather than scrap the slide, which is part of why these machines stay in service for decades.

The ram-type mill is the default machine of toolrooms, maintenance shops, and small job shops because one operator can set up and run almost any milling, drilling, or boring job on it. Typical work spans squaring blocks, cutting slots and pockets, drilling and reaming hole patterns, boring accurate bores with the quill feed, and machining angled faces by tilting the head. Common workholding is a precision vise, a rotary table for arcs and bolt circles, and clamps in the table T-slots for larger parts. The machine's weakness is rigidity at full ram extension, so heavy roughing is done with the ram retracted and the head pulled close to the column where the structure is stiffest, and the long reach is saved for the setups that actually need to get the spindle out over the work.