Introduction to the

Horizontal Mill

Introduction:
The primary difference between vertical and the horizontal milling machine is the spindle is horizontal and in the same plane as the table. As a rule horizontal milling machine do not have a quill that extends from the spindle for drilling, boring, etc. Horizontal mills are able to utilize cutters and attachments that normally would not be practical to use on vertical machines. The milling machine with only three table motions is called the Plain Milling Machine. The following will review the purpose of the plain horizontal mill, the main operating parts of the mill, and some of the machining operations that can be performed on this machine.

The development of the Horizontal Milling Machine:

The old cliché "necessity is the mother invention" holds truth, for American colonist were not legally permitted to manufacture or to import machinery. This forced the Americans to think independently and develop their own designs of machinery. For example the first machine for production in the United States was a textile mill designed by Samuel Slater in 1790 without the benefits of a replica or plans. History notes that France before 1560 as having lathes, however the early development of modern machine tools, lathes, planner, and the shaper are generally credited with England. Planners and shapers are limited in what machining operations can be performed and more diversified machines were needed to meet the new manufacturing demands in the United States. The Plain Horizontal Milling machine is one of those. The Lincoln horizontal mill manufactured by Pratt and Whitney is accredited as being the first. The milling cutter was nothing more than a saw which had exceptionally broad teeth. Once the value of the horizontal mill was recognized new designs rapidly came into being an eventually evolved into sophisticated numerical control machine centers of to day.

Horizontal Milling Machine Functions:

A horizontal milling machine using an arbor is able to employ multiple cutters (mill gang milling) to "side", "face" and "form" machine in one operation. Face cutting can also be performed directly from the spindle. Here the operator is at a disadvantage in that often they are not able to see the cutter performing and still be at the controls in front of the machine. To overcome this problem many manufacturers have additional controls to the side so the machine can be operated from the side and back of the spindle. Although not as convenient as milling machines with a quill that extends from the spindle drilling, reaming, tapping, boring, etc. can be achieved, here the side controls are most helpful.

Horizontal Milling Machine Parts:

Face Cutting With End and Shell Mills:

Face milling is machining a surface at right angles to the axis of the cutter as the work is fed past the cutter. Face cutting can be performed by a variety tools but to step cut end and shell mill is best used. Cutting simultaneously  (90°) require the cutter to have cutting edges on the periphery and face. Both cutters are solid bodies having cutting edges on the periphery and face of the tool and carried at the spindle ether in a holder  or a stub arbor.
Both cutters are made from a single piece of tool steels and become quite expensive in the larger sizes. Replacements cost can be amortize by re-sharpening the cutters but have some disadvantaged in that the cutter is now undersize and less clearance in the flutes.
End mills have from two to six flutes and normally will not exceed two inches in diameter.
Machining softer materials, magnesium, aluminum, plastics, etc. requires coarse cutters such as two and three flutes end mills, six flutes end mills for the hard materials.

Face Cutting Carbide Inserts Blades:

For face cutting carbide inserts blades shell mills are more practical. Carbide inserts cutters operated at speeds and feeds from three to ten times faster than solid body high-speed steel cutters. Also cost for inserts is far less than re-sharpening cost. Inserts cutters work well when only a small periphery step is need or no periphery at all. Cutters with inserts avenge size is ten inch in diameter and are available in larger sizes. The drawback with larger cutters is the machine may not have the power to run at the full potential of the cutter.
Like the solid bodies shell mill the cutter is held in the spindle with a stub arbor.
Blades can be cemented or brazed in position but much more popular is the carbide inserts that are clamped to the cutter body or held with a torx locking screws.
As the cutting edges of the inserts become worn the insert is indexed until all cutting edges are dull. Dull inserts are then discarded and replaced. Inserts are uniformly manufactured at precision tolerances so when replaced there are little or no machine adjustments needed. Also there is added labor saving in that all replacements are made with out removing the cutter.

Supported Arbors:

Supported Arbors are for cutters that the arbor passes completely through and requires a support at the end for rigidity. The most popular style of arbors are   “A” and “B,” both have number 40 or 50 taper and a drawbar thread hole for holding the tool. Of the two types the main difference is that style “A” has a small pilot end for support, style “B” is distinguish by a large support bearing collar that can be position as close to the cutter/s and the arbor support possible to provide maximum rigidity when milling. Other than the support both arbors are the same and come in a number of diameters ranging from 7/8 to 2½ inches. Both have keyway to prevent the cutters from turning on the shaft. In order for the cutters to be in the precise position on the shaft spacers and spacers shims are used and held in this position by tightening the arbor nut. This arbor nut should not be tightened without the arbor support in place for it may bend the arbor. The machine and arbor must be cleaned at the time of setup for dirt and chips will damage the machine and the arbor tapers, and prevent the arbor from running true.

Climb or Conventional Milling:

Machining on a mill is performed by ether climb or conventional cutting and has advantages and disadvantages; this is also known as down or up milling.
1. Climb Milling (also known as down milling). As implied the flutes dig in to material with a climbing action, the workpiece and rotation of the cutter are going in the same direction. With this forward stroke the tooth starts with a full chip and pushes the workpiece down against the table or the holding device.

·        Less machine power is needed.

·        Cutter does not dull as soon.

·        Thin material machine easier.

·        Better for deep and narrow slots.

·        Forms a smoother machine finish.

It is not uncommon to conventional mill to perform the rough cutting and climb mill for the finish cut. Climb cutting can be a disadvantage for older and light machines for the gibs may not hold against the pulling action.


2. Conventional Milling (also known as up milling). Up milling best describes conventional milling for the cutter rotation and the workpiece feed are going in opposite directions; the tool is cutting upward starting with a zero chip thickness and progressively gets thicker until clearing the surface of the part. This is a disadvantage in that the upward motion is pulling the workpiece up and the part must be held secure. Conventional milling is at an advantage for does not have the pulling action of climb milling and allow old or light mills without backlash eliminator to be used.

Summation:

Diversified machines were needed to meet the new manufacturing demands in the United States and the Plain Horizontal Milling machine is one of those machines. Horizontal milling machines can face and drilling operations from the spindle and using an arbor multiple operations such as "gang milling" to "side", "face" and "form."

Cutting on a mill is performed by ether climb or conventional milling and both have benefits.

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