Figure 10-15.--Typical tooth rest blades.
Figure 10-16.--L-shaped tooth rest blade.
firmly against the tooth rest, ensuring a correct cutting
helix cutters, shell end mills, and small end mills. The
edge. If this method causes too much burring on the
offset tooth rest blade (view C, fig. 10-15) is a universal
cutting edge, you may reverse the direction of wheel
blade and you can use it for most applications. Figure
rotation as shown in view A. If you use the latter
10-16 shows an L-shaped tooth rest blade used to
method, be sure the tooth being ground rests firmly on
sharpen metal slitting saws and straight tooth plain
the tooth rest during the cut.
milling cutters with closely spaced teeth. You can make
other shapes of tooth rest blades to fit the specific type
Dressing and Truing
of cutter or the cutter grinder you are using.
Holders for the tooth rest blades may be either plain
You will usually need a soft grade wheel to sharpen
a high-speed steel cutter or reamer. A soft grade wheel
blade in a plain holder and view B shows a tooth rest
breaks down easily and is less likely to burn the cutter.
blade in a universal-type holder. The universal tooth rest
True and dress the wheel before you start the sharpening
holder has a micrometer adjustment at its bottom to help
operation and then redress as necessary, depending on
you make precise up and down movements in the final
the amount of wheel wear. As you grind each cutter
positioning of the blade.
tooth, the grinding wheel diameter decreases because of
wear. As a result, you will remove less metal and the
Setting the Clearance Angle
teeth will gradually increase in size.
To compensate for wheel wear and to be sure all the
teeth are the same size, rotate the cutter 180° and grind
It is essential that the back of the cutting edge of any
all the teeth again. Be careful not to grind the cutter
cutter have correct clearance. If it has too little
clearance, the teeth will drag, causing friction and slow
To ensure a good cutting edge on the cutter, there
cutting. Too much clearance produces chatter and dulls
must be a good finish on the clearance angle; therefore,
the teeth rapidly. The cutting edge must have strength,
you will occasionally need to dress the grinding wheel.
and the correct clearance will provide this strength.
Use the wheel truing attachment for this operation and
for the initial truing and dressing operation on the
produced by grinding.
The primary clearance angle is the angle you grind
when you sharpen a cutter. The number of degrees in
Tooth Rest Blades and Holders
the primary clearance angle vary according to the
diameter of the cutter and the material being cut. A large
Tooth rest blades are not carried in stock, so you
diameter cutter requires less clearance than a small
cutter. Cutters used to cut hard materials such as alloy
must make them in the shop. Once you understand the
requirements for the blades, you can fabricate various
and tool steels require less clearance than cutters used
to cut softer materials such as brass and aluminum.
shapes to suit the types of cutters you will sharpen.
The primary clearance angles range from 4° for a
Normally, these blades should be made of spring steel.
large cutter to 13° for a smaller cutter. Some manu-
Use a plain (straight) tooth rest blade (view A, fig.
facturers of tool and cutter grinders have charts that can
10-15) to sharpen side milling cutters, end mills,
straight-fluted reamers, or any straight-fluted cutter.
help you determine the correct clearance angle. The
Use a rounded tooth rest blade (view B, fig. 10-15) for
width of the primary land (the surface created when you