Tools for Planing Operations | Machine Tools | Industrial Engineering

Planing tools have a relatively large cross-section because they are designed for maximum rigidity. The shank of the tool is made of high strength heat treated alloy steel and inserts are brazed or held mechanically on the shank. By using carbide tools in place of HSS, the planing time can be reduced by about 50%.

The number and variety of cutting tools used on a planer depend upon the shape of the work to be machined on the planer. If the work varies considerably, especially in its form, quite a number of tools of different shapes will be needed. Fig. 15.5 shows some of the typical tool forms and the examples of the kind of planing for which these are adopted. Planing tools are commonly made of high speed steel and tungsten carbide.

The shank of the tool, which has relatively larger cross-section for rigidity, is made of high strength treated alloy steel. Usually negative back rake angle is provided on carbide tools, being higher for tougher materials, i.e., zero degree for soft metals, – 3 to – 5° for C.I., M.S. and – 5 to – 15° for difficult to machine materials.

Side rake of 0 to + 3° is provided for free cutting metals and 0 to – 15° for difficult to machine materials. Side rake controls the chip flow. Excessive negative side rake should be avoided as it may cause chatter.

Optimum side rake eliminates the need for chip breakers. Approach angle for planing tools is 65—70° for most metals. Side and end clearance angles of 5° are used for C.I. and of smaller value for steels. For roughing cuts, relatively small nose radius is preferred. For finish machining of most metals, broad, flat nosed tools (often as wide as 30 mm) are used.

Tool (A) is used for taking deep roughing cuts in cast iron. This style of tool is also made to the opposite hand (B), because it is sometimes desirable to feed the tool toward the operating side of the planer; ordinarily, however, horizontal surfaces are planed by feeding the tool away from the operator, the tool moving from right to left, as viewed from the front of the machine. This enables the operator to see just what depth of cut is being taken at the beginning of the cut.

In tool (A) as the cutting is done by the curved edge e, the front surface b is ground to slope backward from this edge to give the tool keenness, the slope being away from the working part of the cutting edge. The end of flank of the tool is also ground to slope inwards to provide clearance. The angle of clearance (c) is about 4 to 5 degrees. (It may be noted that this clearance is much less than that for lathe tools).

This small clearance is allowable because the planer tool is held about square with the platen, whereas, a lathe tool, the height of which may be varied, is not always clamped in same position. Further in case of lathe tool more clearance is required because it has a continuous feeding movement, whereas a planner tool is stationary during the cut, the feed taking place just before the cut begins.

Thus in planer tool, providing excessive clearance would mean weakening of tool which is not desirable. The slope of the top surface b depends upon the hardness of the metal to be planed, the slope being less for hard material to make the cutting edge more blunt and stronger.

The tool (C) is provided with a broad cutting edge and is used for taking finishing cuts in iron. Tools of this type are made in various widths and when planing very large and rigid castings, wide cutting edges and coarse feeds are used. The coarse feed is used because the tool has to remove the ridges left in rough planing with a round nose tool; consequently, the cuts are comparatively light and the tool can be given a large feeding movement.

The feeding movement must be, however, somewhat less than the width of the flat cutting edge to provide some overlap and prevent the formation of ridges. Wide finishing tools (C) for cast iron are sometimes ground so that the cutting edge slopes back at an angle to give a shearing cut.

The edge of a broad cast- iron finishing tool should be ground straight by testing it with a small straight edge or scale. The corners should be rounded slightly because a square corner on the leading side will dull quickly.

Tool (D) is a plain round nose tool and is often used for rough planing steel or wrought iron. It can also be made into a finishing tool for the same metals by grinding the nose or tip end flat. The width of the flat cutting edge is much less, however, than for cast iron finishing tools, because steel offers a greater resistance to cutting than cast iron.

Tool (E), known as diamond point tool, is also used for rough planing steel or iron and for taking light cuts. The diamond point is ground with a narrow rounded point. This is useful when a light cut is necessary, either because the work cannot be held securely for planing or for some other reason.

The bent tools (F) and (G) are used for planing either vertical surfaces or those which are at a considerable angle with the platen. These are right and left-side roughening tools, and are adopted to either cast iron or steel. They can also be used for finishing steel. In tool (F), as the cutting is done by edge e, the face b [similar to that shown for tool (A)] should slope back from edge e.

Tools (H) and (I) are used for finishing vertical or angular cast iron surfaces. These have wide cutting edges to permit coarse finishing feeds. Vertical surfaces can often be planed to better advantage by using a straight tool in the side-head, when the planer is so equipped.

Tools (J) and (K) are right and left angle tools used for planing angular surfaces which, by reason of their relation to horizontal or other surfaces, can only be finished by a tool having a pointed form as illustrated.

A typical example of the kind of angular planing requiring the use of an angle tool is indicated in the illustration. After finishing side a, the horizontal surface b (from which a roughening cut should have been taken previously) could be planed feeding the same tool horizontally.

Tool (L) is a square-nose tool and is used for cutting slots and squaring corners, and the same style of tool is made in different widths. As the square-nose tool cuts along its lower edge e, it should be given clearance c on the end and sides, as shown in the two views. The longer edge is the widest part of the cutting end, the sides sloping inward in both the vertical and horizontal directions, which prevents the tool from binding as it moves through a narrow slot.

Tool (M) is a narrow square nose or parting tool and is used for cutting narrow grooves. It can also be used for cutting a part in two, provided the depth does not exceed the length of the narrow cutting end.

Tools (N) and (O) are known as right and left side- tools. These can frequently be used to advantage on vertical or angular surfaces. It cuts along edge e which, as the side view shows, slopes backward. Though planer side tools are not always made in this way, it is a good form as the sloping edge starts a cut gradually whereas a vertical edge takes the full width of the cut suddenly, producing a greater shock.

Tool (P) is used for planing brass. It has a narrow rounded cutting edge and very much like a brass turning tool. For finishing cuts in brass, tools having narrow flat ends are often used. Tools (Q) and (R) are right and left bent, square nose tools used for cutting grooves or slots in vertical surfaces and for similar operations.

The tool (S) is used for rounding edges. Tools of this type are sharpened by grinding on the front face only, in order to retain the curved edge. (In the sharpening of tools other than formed tools, the grinding is done both on the face and end, because a sharp edge can be secured more quickly by this method).

Tool (T) is known as goose-neck type of tool because of its shape. It is a peculiar shaped tool and is especially adopted for finishing. This tool is intended to eliminate chattering and the tendency which a regular finishing tool has of gouging into the work, particularly if the planer is not in good condition.

By referring the side view it will be seen that the cutting edge is on a line with the back of the tool shank, so that any backward spring of the tool while taking a cut would cause the cutting edge to move along an arc c or away from the work.

When the cutting edge is in advance at position x, as with a regular tool, it will move along and arc d, if the strain of the cut causes any springing action, and the cutting edge will gouge in below the finished surface. Ordinarily the tool and the parts of the planer which support it are rigid enough to prevent such a movement, so that the goose neck tool is not always necessary.