3. Milling Machine Accessories And Attachments

3. Milling Machine Accessories And Attachments
a. Arbors. Milling machine cutters can be mounted on several types of holding device. The
machinist must know the devices, and the purpose of each to make the most suitable tooling
setup for the operation to be performed. Technically, an arbor is a shaft on which a cutter is
mounted. For convenience, since there are so few types of cutter holders that are not arbors,
we will refer to all types of cutter holding devices as arbors.
(1) Description.
(a) Milling machine arbors are made in various lengths and in standard diameters
of 7/8, 1, 1 1/4, and 1 1/2 inch. The shank is made to fit the tapered hole in the
spindle, the other end is threaded.
NOTE
The threaded end may have left-handed or right-handed threads
.
(b) Arbors are supplied with one of three tapers to fit the milling machine spindle
(figure 4), the milling machines Standard taper, the Brown and Sharpe taper, and
the Brown and Sharpe taper with tang.
(c) The milling machine Standard taper is used on most machines of recent
manufacture. It was originated and designed by the milling machine
manufacturers to make removal of the arbor from the spindle much easier than will
those of earlier design.
(d) The Brown and Sharpe taper is found mostly on older machines. Adapters or
collets are used to adapt these tapers to fit the machines whose spindles have
milling machine Standard tapers.
(e) The Brown and Sharpe taper with tang also is used on some of the older
machines. The tang engages a slot in the spindle to assist in driving the arbor.
(2) Standard Milling Machine Arbor (figure 4, and figure 5).
(a) The Standard milling machine arbor has a straight, cylindrical shape, with a
Standard milling taper on the driving end and a threaded portion on the opposite
end to receive the arbor nut. One or more milling cutters may be placed on the
straight cylindrical shaft of the arbor and held in position by means of sleeves and
an arbor nut. The Standard milling machine arbor is usually splined and has keys,
used to lock each cutter to the arbor shaft. Arbors are supplied in various lengths
and standard diameters.
(b) The end of the arbor opposite the taper is supported by the arbor supports of
the milling machine. One or more supports are used, depending on the length of
the arbor and the degree of rigidity required. The end may be supported by a lathe
center, bearing against the arbor nut (figure 4) or by a bearing surface of the arbor
fitting inside a bushing of the arbor support. Journal bearings are placed over the
arbor in place of sleeves where an intermediate arbor support is positioned.
FIGURE 4. STANDARD MILLING MACHINE ARBOR INSTALLED.
(c) The most common means of fastening the arbor in the milling machine
spindle is by use of a draw-in bolt (figure 4). The bolt threads into the taper shank
of the arbor to draw the taper into the spindle and hold it in place. Arbors secured
in this manner are removed by backing out the draw-in bolt and tapping the end of
the bolt to loosen the taper.
(3) Screw Arbor (figure 5). Screw arbors are used to hold small cutters that have
threaded holes. These arbors have a taper next to the threaded portion to provide
alignment and support for tools that require a nut to hold them against a tapered
surface. A right-hand threaded arbor must be used for right-hand cutters; a left-hand
threaded arbor is used to mount left-hand cutters.
(4) Slitting Saw Milling Cutter Arbor (figure 5). The slitting saw milling cutter arbor is a
short arbor having two flanges between which the milling cutter is secured by tightening
a clamping nut. This arbor is used to hold the metal slitting saw milling cutters that are
used for slotting, slitting, and sawing operations.
(5) End Milling Cutter Arbor. The end milling cutter arbor has a bore in the end in which
the straight shank end milling cutters fit. The end milling cutters are locked in place by
means of a setscrew.
(6) Shell End Milling Cutter Arbor (figure 5). Shell end milling arbors are used to hold
and drive shell end milling cutters. The shell end milling cutter is fitted over the short
boss on the arbor shaft and is held against the face of the arbor by a bolt, or a retaining
screw. The two lugs on the arbor fit slots in the cutter to prevent the cutter from rotating
on the arbor during the machining operation. A special wrench is used to tighten and
loosen a retaining screw/bolt in the end of the arbor.
(7) Fly Cutter Arbor (figure 5). The fly cutter arbor is used to support a single-edge
lathe, shaper, or planer cutter bit, for boring and gear cutting operations on the milling
machine. These cutters, which can be ground to any desired shape, are held in the
arbor by a locknut. Fly cutter arbor shanks may have a Standard milling machine
spindle taper, a Brown and Sharpe taper, or a Morse taper.
FIGURE 5. TYPES OF MILLING MACHINE ARBORS.
b. Collets and Spindles.
(1) Description. Milling cutters that contain their own straight or tapered shanks are
mounted to the milling machine spindle with collets or spindle adapters which adapt the
cutter shank to the spindle.
(2) Collets. Collets for milling machines serve to step up or increase the taper sizes so
that small-shank tools can be fitted into large spindle recesses. They are similar to
drilling machine sockets and sleeves except that their tapers are not alike. Spring collets
are used to hold and drive straight-shanked tools. The spring collet chuck consists of a
collet adapter, spring collets, and a cup nut. Spring collets are similar to lathe collets.
The cup forces the collet into the mating taper, causing the collet to close on the straight
shank of the tool. Collets are available in several fractional sizes.
(3) Spindle Adapters. Spindle adapters are used to adapt arbors and milling cutters to
the standard tapers used for milling machine spindles. With the proper spindle adapters,
any tapered or straight shank cutter or arbor can be fitted to any milling machine, if the
sizes and tapers are standard.