Milling cutters with side teeth are called side milling cutters.
These are used to machine steps and grooves or, when only the sides of the workpiece are to be machined, in straddle setups. An example is cutting hexes on bolt heads. Grooves are best machined in the workpiece with full side mills that have cutting teeth on both sides (Figure K-71). Steps may be cut with half side mills having cutting teeth only on one side (Figure K-72).
The size, type, and diameter of side milling cutter to use will depend on the machining task. As a rule, the smallestdiameter cutter that will do the job should be used as long as sufficient clearance is maintained between the arbor support and work or vise.
A good machinist will mark the workpiece with layout lines before securing it in the machine. The layout should be an Figure K-71 Full side milling cutter machining a groove.
exact outline of the final part shape and size. The reason for making the layout prior to beginning work is that reference surfaces are often removed during machining. After the layout has been made, diagonal lines should be chalked on the workpiece indicating the portions to be cut away. This helps Before you use a milling cutter, inspect the cutting edge for sharpness. If the cutting edge of the tool shows any
sign of wear or dullness, it should be sharpened. Milling cutters need to be sharpened on a tool and cutter grinder so that every cutting edge is exactly in the same cylindrical plane as every other one. If one cutting edge extends beyond any other, it will produce a wavy or scalloped
surface on the machined workpiece.
Dull milling cutters create excessive cutting pressures that may distort the workpiece or move it from the work-holding device.
Milling cutters leave a rough surface finish if they need to be sharpened.
identify on which side of the layout lines the cut is to be made (Figure K-73). The workpiece may be mounted by any of the traditional methods discussed previously. If you are using a vise, be sure it is aligned along with the table. If you are clamping directly to the table, follow the rules of good clamping.
Frequently, side milling cutters will cut a slot or groove slightly wider than the nominal width of the cutter. The causes of this can be cutter wobble due to small chips or dirt between the cutter and spacing collars or multi- ple passes through the workpiece. Other factors influ-
encing the width of cut are the feed rate and/or the type of material being machined. A slow feed rate will allow the cutter to make a wider slot; this can also happen when softer materials are machined. If the drawing calls for a slot width of .375 in., using a .375-in.-wide cutter
may result in a slot .3755 to .376 in. wide. To achieve the correct slot width, a 250-in.-wide cutter may have to be used and multiple passes made. However, if a slot slightly wider than the cutter width is needed, using a shim between the cutter and the spacing collar may
give the desired results. Remember to use shims on opposite sides of the cutter, 180 degrees apart. The resulting wobble will make an oversized slot. The faces of arbor spacing collars may be lightly stoned to remove burrs. This technique may also result in reduced cutter
Positioning a Side Milling Cutter
To machine a slot or groove at a particular location on the workpiece, the side mill must be positioned both horizontally (for location) and vertically (for depth of cut). To position the cutter for location, lower below the top surface of the workpiece. With the spindle off and free to turn by hand, insert a paper strip between cutter and work (Figure K-74) and move the workpiece toward the cutter until the paper is pulled
between the work and cutter. At this point, the cutter is about .002 in. from the workpiece. Set the saddle micrometer collar to zero, compensating for the .002 in. of paper thickness.
Position for depth by lowering the knee and moving the workpiece under the cutter. Then, raise the knee and use the paper strip gage to determine when the cutter is about .002 in. above the workpiece. Set the knee micrometer collar to zero. Move the table until the cutter is clear of the workpiece, and then raise the knee the amount required for the depth of the feature.
A less accurate but quicker method of cutter alignment is direct measurement (Figure K-75). A rule may be used to measure the position of the cutter relative to the edge of the workpiece, after which the saddle micrometer collar should be set to zero.
Making the Cut
After the cutter has been positioned for location, raise the knee the amount required for the depth of the cut. Machining to full depth may be accomplished in one pass, depending on the width of the cut and the material being machined. A deep slot may have to be machined in more
than one pass, each pass somewhat deeper than the one before. Until you gain experience in milling, hold the depth setting to about .100 in.
Set proper feeds and speeds and turn on the spindle.
Approach the workpiece in an up-milling mode. Hand feed the cutter into the work until a small nick is machined on the corner (Figure K-76, point X). Stop the spindle, back away, and check the dimension relative to the edge of the workpiece. If you are machining a slot, check the width with an adjustable parallel and a micrometer (Figure K-77), or use a dial/vernier caliper. If the dimensions are correct, complete
the required cuts. Precise depth can be measured with a depth micrometer (Figure K-78).
Side milling is an excellent way to machine a shaft keyseat, especially if the keyseat is quite long. The procedure for keyseat milling is much the same as in vertical milling.
The cutter must be centered over the shaft and set for depth. After selecting and mounting a cutter of the proper width, raise the workpiece beside the cutter and use the paper feeler technique to position the cutter alongside the shaft. Lower the knee and move the workpiece over a distance equal to half the total of cutter width plus shaft diameter. Raise the knee until the cutter contacts the shaft and cuts a full width cut.
Set the knee micrometer collar to zero. Lower the knee and move the cutter clear of the workpiece in the table axis only. Raise the knee to obtain the correct keyseat depth. Using proper feeds and speeds, approach the workpiece in an upmilling mode,and mill the keyseat to the proper length.
Side milling cutters are combined to perform straddle milling.
In straddle milling, two side milling cutters are mounted on an arbor and set at an exact spacing (Figure K-79). Two sides of the workpiece are machined simultaneously, and final width dimensions are exactly controlled. Straddle milling has many useful applications in production machining. Parallel slots of equal depth can be milled by using straddle mills of equal diameter.
Interlocking side mills are used when grooves of a precise width are machined in one operation (Figure K-80). Shims inserted between individual cutters make precise adjustment possible. The overlapping teeth leave a smooth finish in the bottom of the groove. Cutter combinations that have become thinner from resharpenings can also be adjusted to their full width by adding shims.