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The horizontal boring mill is not a high-volume production machine. Instead, it’s a versatile machine able to conform to a number of machining operations including boring, drilling, milling, reaming, tapping, threading, turning, shaping, forming and duplication. Machines such as the horizontal boring machine were made precisely for their rigidity and versatility. A direct descendant of Wilkinson’s boring machine which made James Watt’s steam engine practicable in eighteenth century England. The horizontal boring mill was developed to perform a number of applications in just one setup. For example, a workpiece can be produced by carrying it from one machine to another of the four basic types; lathe, drill, mill and planer & shaper. Manufacturing parts by moving them from one machine to another is impractical, especially involving large and heavy pieces. Also, every time a part was moved to another machine, new possibilities for error would be introduced and difficult to hold close tolerances. The principal parts of the horizontal boring mill parallel the heavy work that is done on the machine.

PRINCIPAL PARTS
Headstock - The unit which supports the drives and feeds the tool. May contain one or two spindles, one slow-moving for heavier operations of boring and one fast-moving for lighter operations such as drilling and tapping.
Column base - Supports the column and houses the gears and driving mechanisms. For floor types the base is mounted so the spindle is at right angles to the ways of the runway while table types have the spindle parallel to the runway.
Column - Gives support for headstock while accurately guiding it up and down on ways. It also balances the headstock since it’s constructed hollow in order to house counterweights, making it easier to move.
End support column - Supports the end of the bar when a line bar is used. Table type machines have the end-support’s bearing block traveling in unison with the headstock while the floor type’s end support adjusts separately aligning the headstock through the use of a scale and vernier.
Runways - Used to hold the main column, end-support column and a rotary table (if needed).
Table - Provides the locking and clamping of the work, a support for holding the workpiece. The table generally travels at right angles to the axis of the spindle unless equipped with a saddle.
Saddle - Lets the table move axially and transversely to the spindle.
Bed - All table and planer type machines have beds. Stores the coolant tank and supports the column, headstock, end supports, and table.
Floor plate - Made from several pieces and is mounted and leveled into position.
There are two basic types of horizontal boring mills, table-type and floor-type. The table-type and floor-type horizontal boring mills differ in their applications. In a tabletype machine, the workpiece is set up on the machine table and is moveable, so that the work can be brought to the machine. For floor-type units the reverse occurs where the workpiece is fastened down onto the floorplates, and the spindle travels to the work. The table-type is more favorable towards machine accuracy and versatility of metal removal. Other types include planer-type, which resembles the table-type, but with a reciprocating table the piece moves past the tool on a bed in the same manner as in a planer. Mostly used for long work or where rigidity is needed. Multiple-head types is the only machine of the horizontal boring mills that can do vertical as well as horizontal boring or milling, useful for working on V-type engine blocks. Precision boring machines are primarily designed to bore holes in small machine parts. It’s performed with a single-point tool at high cutting speeds in order to produce accurate and finished hole sizes.

SELECTION
When making a decision on evaluating equipment, the horizontal boring mill is flexible in housing operations of large or complex parts with high production volume. Make sure when selecting a machine that it will be able to satisfy your production requirements and can turn out finished work at a lower cost per unit more so than any other type of machine. In order to do this, you must be familiar with the many capabilities and options a horizontal boring machine can provide.
In many operations the horizontal boring mill is an adapter that is used between the spindle and the cutting tool. Cutting tools are placed in many bars that send motion and power passed on by the machine spindle. The technique behind the bar support varies to correspond with the length of the bar required to reach the cut, how accessible the bore is, and the degree of stringency of the finish. When doing hole work on a horizontal boring mill the tool is rotated. To move from one position to another, either the spindle or the workpiece is traversed, depending on the machine type used. Other processes such as reaming, counterboring and tapping are done in a similar fashion. Depending on what kind of boring needs to be done, there are primarily two types of boring bars used: stub bars and line bars. Stub bars are supported at the spindle end and are used to bore holes that are situated comparatively close to the headstock. Regular boring bars have various slots along their length where a flat type of cutter can be inserted. Some cutters have a setscrew adjustment, others are located by an accurate slot. The tool itself may have one cutting edge or two where there is one on each side of the boring bar. Additional cutters of two or three are mounted at times to handle roughing, intermediate, and finishing cuts in just one setup. Boring fixtures, used for increasing the productivity of the machine, operate to support the workpiece and align it to the bar before boring begins. Any type of milling cutter can be used for milling work on a horizontal boring mill. Grooves, slots and holes can be performed by end mills. Facing cutters finishes all sorts of flat surfaces. Circular grooves can be machined around the workpiece with any number of special operations that need to be performed. The two most important structural features of the horizontal boring mill are its rigidity of construction and durability of working parts. Since these machines in many cases are in operation continuously, the rigid construction and durability become essential for this type of precision work. With the recent age of computer-aided design, these machines now produce greater accuracy at lower weights. Another important consideration is the inherent accuracy of the machine. Usually, large workpieces will require extremely close tolerances whereas small ones require looser tolerances. The versatility of the horizontal boring mill can be flexible enough to fit many different machining operations, so it’s important for the user to select and purchase the model best suited for their jobs.

INSPECTION
NON-POWER
These inspections can be made with a leveling device.

For table-types:
Make sure the machine bed is level transversely and longitudinally.
Examine all ways for wear and scores.
Make sure the table top is parallel to the bed ways.
Check all hoses, cables and plugs for any damage.
Make sure the table edge is parallel to the saddle guiding edge.
Make sure the table edge is square with the spindle.
Verify that the spindle is parallel with the table top, saddle, and the longitudinal travel.

For floor-types:
Make sure the spindle is parallel with the floor plate.
Check that the spindle is aligned with the edge of the bed and the longitudinal travel.
Make sure the vertical travel of the headstock is perpendicular to the working surface.
Look for any pitch and roll of the column slide on its runway.
Confirm that the T-slots and floor plate edge are parallel to the runway ways.

UNDER-POWER
Look for spindle concentricity through the use of a dial indicator.
Inspect for spindle sleeve face run-out with the use of the dial indicator.
Make sure the gears seem to be working and sounding smoothly, listen for any peculiar sounds.
Test the speed gear boxes through all speed ranges, making sure they run quietly and properly.
Test the feed gear box through all feeds.
Run the machine through a complete cycle, verifying all systems are working properly.
Check the emergency stop buttons.

*This is one article in a series of How to Buy Metalworking Equipment. Each article showcases and explains a particular type of metalworking machine. They were originally published in the Metalworking Machinery Mailer published by the Tade Publishing Group.