Work of a Shaper | Machine Tools | Industries | Engineering

Shaper work is generally limited in size by the maximum length of stroke of the shaper ram. The shaper can machine a variety of plane surfaces, profiles, and contoured surfaces when equipped with a tracing attachment. Much of the work performed on shapers is done with the workpiece held in a shaper vise.

The bottom of the shaper vise is an accurate locating surface that is parallel to the base. One jaw of the vise is a stationary jaw while the other jaw is movable. The stationary jaw forms a second locating surface and must be kept perpendicular to the bottom of vise. The movable jaw should not be used as a locating surface because the clearances that are necessary for it to slide without binding allow it to tip slightly.

Generally both the jaws have heat-treated steel inserts. The shaper vise has a swivel base graduated in degrees and it permits the vise jaws to be positioned parallel, perpendicular, or at an angle with respect to the stroke of the ram.

The cut is adjusted by lowering the tool-box on its slide on the end of the ram, and the flat surface is then generated by reciprocating the tool across the work, and imparting a horizontal feed motion to the work table. It is very important for accurate work that the shaper vise as well as the shaper table be ascertained for their accuracy.

Holding the Work in Vise:

The work may be held in a vise without additional tools when it is large enough so that the stock to be removed is above the vise jaws. Thin stock may be raised to a convenient height in the vise by placing a pair of parallels under the work. A round bar of soft metal (for a steel wedge) is found to be helpful in preventing wide pieces of material from being forced out of the vise.

Fig. 14.10 shows how a hold-down wedge can be used to force the workpiece against the solid or reference jaw of the vise to help insure that the surface being cut is perpendicular to the finished surface. It may be noted that rough and hard surfaces of castings can damage the finished jaws of the vise. To protect jaws, some compressible material like emery cloth is used between the workpiece and jaws of vise.

Fig. 14.11 shows the use of a cylinder of soft metal to provide line contact on the edge of work. This prevents the movable jaw from providing a lifting movement to the work as the screw is tightened. As the work is tightened, it is tapped onto the parallels with a Babbitt hammer and the free jaw of vise takes some play. After tightening, the parallels are checked so see that they are firmly in contact with the bottom of the workpiece.

The finished surfaces of the shaper vise and all other precision machinist’s vises should always be protected from being marred by rough unfinished surfaces of castings, forgings having a rough mill scale. This is done by placing shims made of soft aluminium, copper or brass sheet between the workpiece and the finished surfaces of the vise. When seating the work on parallels, it should be given a ‘dead’ blow with a lead hammer {i.e. hammer should not bounce away from the workpiece).

The rough workpiece is taken as seated in vise if one of the parallels is tight. Actually it is not possible to seat the rough work on both parallels because the rough surfaces can’t be square or parallel with each other. The vise should not be tightened further after the work-piece has been seated as this may cause it to become unseated.

The tool holder should be set in the tool post such that the tool bit does not extend further than 50 mm from the tool post.

It has been found that chattering is caused on the shaper if:

(i) The tool is suspended too far from the tool holder,

(ii) The work is not held rigidly in the vise, or

(iii) The ram gibs are not adjusted properly.

The chattering, however, can be eliminated by:

(i) Regrinding the cutting tool for less front clearance,

(ii) Reducing the distance between the tool and the work,

(iii) Retightening the work in the vise or on the table,

(iv) Adjusting the jibs of the ram for a minimum of clearance.

It is important to note that a hammer should not be used on the handle of a vise in an effort to tighten it.

The vise handle being long enough, application of little pressure at the end may exert excessive pressure to clamp the jaws tightly on the work. While shaping a plane surface, the clapper box of the shaper should be tilted so that the top slants slightly away from the cutting edge of the work (Fig. 14.12).

This causes the cutting tool to swing away from the shoulder made by the tool during the cut when the ram is making its return stroke. Further it is essential that the tool be clamped in a vertical position so that it will swing out of the work if it slips. The shaper table should be so adjusted that the overhang of the tool slide is minimum.

The length and position of the ram stroke should be so adjusted that the tool clears the ends of the work by approximately 20 mm at the beginning and approximately 10 to 15 mm at the end of the cutting stroke.

Checking Jaw of Vise being Square with the Stroke of the Ram:

For this purpose first fasten the vise securely to the table with the solid jaw towards the ram. Place an indicator in the tool holder so that the point of the indicator touches the finished surface (Refer Fig. 14.13). Note the movement of the indicator as the vise is moved perpendicular to direction of stroke with the aid of the cross-feed.

Checking Jaw of Vise for being Parallel with the Stroke of the Ram:

For checking that the solid jaw of the vise is parallel with the stroke of the ram, fasten the vise securely to the table with the edge of the solid jaw parallel to the ram. Place an indicator in the tool holder with the point of the indicator touching the finished surface of the jaw (Fig. 14.14).

Note the movement of the indicator as the ram is moved slowly back and forth. In case it is found that the work is not parallel within reasonable limits, after a cut has been taken from each side of the work, then vise should be inspected thoroughly for dirt and chips and it should be made sure that it is clean. If this does not correct the condition, then vise jaw should be checked with an indicator.

Checking the Work for being Level with the Surface of the Table and Parallel with the Slide of the Table:

For most jobs, the surfaces may be checked with a surface gauge as shown in Fig. 14.15 by sliding the surface gauge along the table and noticing any variations.

However, when a more accurate check is required, an indicator may be fastened to the tool holder, and moved across the surfaces with the aid of the cross-feed or the movement of the ram.

Holding the Work on Table:

In certain cases (very large pieces, odd shaped jobs) it may not be convenient to hold the workpiece in the shaper vise.

Most jobs can be securely held by means of clamps which are bolted to the table with T-bolts (Fig. 14.16). In this case it should be ensured that the clamping force is directed towards the work than the block that is used to level the clamping strap. A block in conjunction with thin metal shims of suitable height is placed under one end of the clamp to keep it level.

A thin piece of work may be held with the help of toe dogs combined with the use of a stop (Fig. 14.17). These exert a downward force on the work-piece to hold it to the shaper table. Several pairs of toe dogs would be used to hold the work, according to the length of the material.

The top and front views of the toe dog are shown in Fig. 14.18.

Shaper can be conveniently used for internal shaping works like internal key waying. Fig. 14.19 shows shaping of four internal square holes in a plate without change of set up. Proper tooling is required for carrying out internal shaping jobs on a horizontal shaper.

Fig. 14.20 shows the use of a shaper for shaping splined shafts with a set of index centres. Similarly it can be used for shaping internal gears also. Large awkward castings can be secured to the machine with supplementary table tops. Many unusual shaping works like knurling, marking etc. can be carried out using special fixtures or even special shapers.

Fig. 14.21 shows a special shaper (hydraulically operated) with two tool heads. Other special shapers are tandem shapers, draw-cut shapers etc. and these require special fixtures for mounting and feeding the work.

Shaper and Planer Tools:

Since shaper and planer tools cut with shock at the start of each cutting stroke, these must have more adequate support beneath the cutting edge than in other turning tools.

Since shaping speed is low, HSS is commonly used for shaping tools. Carbide tools are prone to chip due to impact force at beginning of cut and interrupted cutting.

As shaper and planer tools cut in one direction only, a side rake angle is seldom ground on them. Because the tool is fed, or is moved into position to cut, on the return stroke of the machine only, the clearance angle may be less than on lathe tools. The front clearance should be 3—4 degrees when the tool is in the cutting position (Fig. 14.22).

The reason for the minimal clearance is to provide support for the cutting edges. As speed is low, high-speed steel tools are used. Most of the tools used in the shaper are of high speed steel, with preference towards grades having high vanadium for better shock resistance.

Carbide tools are generally not used because they are prone to chip, but may be used for making finishing cuts on die blocks or for shaping difficult-to-machine materials, hard and abrasive materials.

Some examples of tool bits ground for use on shapers and planers are shown in Fig. 14.23.

Roughing tool should remove as much stock as possible (the depth and feed being maximum) consistent with the power and rigidity of the machine, the strength of the tool and the strength of the workpieces, leaving about 0.25 mm material to be removed by finishing cut.

To reduce cutting force, feed should be lessened before a reduction in depth of cut. On cast iron, roughing cut should completely penetrate the scale on the first cut. The tool would dull very quickly if it rides upon the scale.

Chatter would be experienced if the adjustment of machine gibs is poor, or overhang of tool, tool slide or workpiece is excessive. Chatter can be reduced by checking all above points, and limiting the radius on the point of the tool to 0.75 mm or less.

Tool should be mounted as close into the tool post as possible and the toolslide overhang should be minimum possible. Tools should be kept sharp and the cutting edges honed after grinding to give the longest possible tool life.