End mills are made in a wide variety of types. We can attribute this to how many different places they’re used on machines and parts in industry. End mills are used to do work in various positions in the vertical heads of universal milling machines. These tools are held either directly in the spindle socket or in the head’s collets, using collet chucks.
Milling with an End Mill
There are also indexable-insert end mills. Because of their profile, end mills are generally used for operations like pocket milling and slotting.
When people think of end mills, cutting keyways in shafts usually comes to mind, but they’re also used for various other milling operations. For example, machining die components, drilling and enlarging holes, and hollowing out interior sections (pocket milling).
The image above shows a clamping-shoe slot being hollowed out with an end mill.
In the image above, a helical-flute, multi-tooth end mill that cuts on both the face and the periphery has been mounted in the machine’s universal head socket using a draw-in bar. However, it’s been rotated at an angle from the head, appropriate for the machining inside the hole. The workpiece is clamped to the table with a clamping shoe, packing block, and bolts, and a slot, or a pocket according to a drawing, is being machined inside it.
Above is an example of end-mill machining on a multi-axis vertical CNC machining center using CAD/CAM. End mills are used a great deal, especially in mold making, to machine pockets and detail surfaces.
Points to Pay Attention to When Milling with an End Mill
1 — The tip of the end mill must not be crashed into the workpiece while positioning it. It can break or run out.
2 — The clamping method should be chosen to match the shank’s shape.
3 — Unlike a drill, the tip of an end mill can’t feed along its own axis. It can only plunge by a limited amount.
4 — Since these cutters mostly cut with their side surfaces, their tips wear quickly. The worn amount can be reground on the face, but only peripheral, surface cuts should then be taken.
5 — On end mills, deep cuts that could flex the teeth where they join the shank should not be taken.
6 — In general, multi-tooth end mills with helical or straight flutes are used for milling surfaces, while 2-, 3-, and 4-tooth end mills are used for cutting various slots and for drilling operations that feed along a fixed axis.
Since these cutters, used for various cutting operations, are known to dull quickly, the explanations above should be followed carefully.
Slotting with an End Mill
When cutting keyways in shafts, it’s important to take the necessary care while using end mills. Otherwise, this rather expensive cutter can naturally be destroyed in an instant.
To illustrate this, pay attention to the explanations below.
The shaft is marked along its axis according to the type of keyway to be cut on it — that is, whether it’s open at one end or closed at both ends.
The workpiece is clamped in the vise or on the table with special clamping tools. If the shaft is being mounted on the table, the table is seated lengthwise in the “T” slots; if that’s not possible, it should be mounted on V-blocks, using clamps and bolts. The same shaft can, in a different setup, be mounted with a three-jaw universal chuck and a center, or directly between two centers.
Zeroing When Slotting with an End Mill
As shown at the side, the milling cutter is brought up to the side of the workpiece. With a piece of paper placed between them, the table is brought closer with the carriage until the paper tears. When it starts to tear, the cross-feed micrometer collar is set to zero. After setting the cutter’s side surface, the table is lowered from the knee.
For example;
If the end mill’s diameter is 12 mm and the workpiece’s diameter is 30 mm, since the paper’s thickness is 0.025 mm (which can be ignored), when the paper tears, the table’s position is,
12/2 + 30/2 + 0.025 =
6+ 15 + 0.025= 21.025 mm. The table is advanced this much from the micrometer collar.
The end mill can also be set to the workpiece’s axis using other methods, but
the method above is the most convenient.
Setting the end mill to the shaft’s axis when milling with an end mill is shown separately in the drawings above.
Set from the side surface, the cutter is brought onto the workpiece’s axis as shown above; here, zeroing is done so it’s tangent to the shaft, and the desired depth is then given.
The keyway is then cut using the appropriate cutting speed and feed for the end mill. If both ends of the slot are closed, a “two-flute” end mill should be chosen here. But if a multi-tooth end mill is going to be used, a hole of the appropriate depth should first be drilled at each end of the slot. This is because multi-tooth end mills can’t feed along their own axis — they’ll break.
At the end of the operation, it’s measured, checked, and cleaned up.
If the ends of the keyway are open, a cutter thin enough to enter from outside the part — a slot mill — can be used; or if the shaft diameter is large, small-diameter “T” slot cutters can also be used.
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