Shaping is a machining process in which a single-point cutting tool moves with a reciprocating motion relative to the workpiece. Material is normally removed during the forward stroke, while the return stroke repositions the tool ready for the next cutting stroke.
Shaping machines were important during the development of machine tools and were widely used for producing flat surfaces, slots and other features. They are much less common in modern production because milling, broaching, grinding and CNC machining can usually provide greater productivity and flexibility.
The shaping process nevertheless remains useful for understanding single-point cutting, reciprocating machine mechanisms and the production of geometrical features using relatively simple tooling.
In a conventional shaper, the cutting tool is mounted on a reciprocating ram. The workpiece is secured to a table beneath the tool.
A typical machining cycle consists of:
On many mechanical shapers the return stroke is arranged to take less time than the cutting stroke. This reduces the time spent on the non-cutting part of the cycle and is commonly known as a quick-return motion.
Although machine designs vary, the principal elements of a conventional shaper include:
| Part | Function |
|---|---|
| Base and column | Provide the main machine structure and support the reciprocating mechanism. |
| Ram | Reciprocates relative to the workpiece and carries the cutting-tool assembly. |
| Toolhead | Supports and positions the cutting tool and provides adjustment for the required cutting geometry. |
| Clapper box | Allows the tool to lift or move away from the machined surface during the return stroke on machines using this arrangement. |
| Table | Supports the workpiece, vice or fixture and provides positioning and feed relative to the cutting tool. |
| Cross-rail and saddle | Provide adjustment and support for positioning the table on conventional shaper designs. |
| Drive mechanism | Converts rotary drive into the reciprocating motion required by the ram. |
A mechanical shaper requires rotary motion from the machine drive to be converted into reciprocating motion of the ram. Various mechanisms have been used to achieve this movement.
The mechanism illustrated below produces the reciprocating ram movement. The arrangement can be adjusted to alter the stroke length and the position of the stroke so that the cutting movement corresponds with the location and length of the workpiece.
A quick-return mechanism is arranged so that the ram completes the non-cutting return movement in less time than the cutting movement. The return stroke therefore occurs at a higher average velocity.
For further information on mechanisms used to generate reciprocating motion see: Reciprocating Motions .
Shaping uses single-point cutting tools similar in principle to those used for turning. The tool geometry is selected according to the workpiece material, direction of cut and surface or feature being produced.
Because the cutting action is intermittent, the cutting tool is repeatedly loaded and unloaded during operation. The toolholder, toolhead and machine must therefore provide adequate rigidity while allowing the tool to clear the workpiece during the return stroke.
Simple tool shapes can be ground for particular operations, which was historically one of the attractions of the shaping process. Flat surfaces, slots and special forms could be generated without requiring a complex multi-edge cutter.
Many conventional shapers use a hinged toolholder arrangement known as a clapper box. During the cutting stroke the tool is supported against the cutting force. During the return stroke the arrangement permits the tool to move away from the newly machined surface rather than dragging the cutting edge heavily across it.
The required toolhead and clapper arrangement depends on the direction of cutting and the feature being machined. Particular care is required when shaping vertical or angled surfaces because the tool must clear the workpiece correctly during the return movement.
The versatility of the shaping machine comes from the ability to control the direction of the cutting stroke, the feed direction and the geometry of the single-point cutting tool.
Typical shaping operations include:
Flat surfaces are among the most straightforward features produced on a shaper. The cutting stroke passes across the workpiece and a small feed movement is applied between successive strokes.
The final surface is therefore generated by a series of adjacent single-point tool paths. Tool geometry, feed, machine rigidity and the condition of the cutting edge influence the resulting surface finish.
One advantage of single-point reciprocating machining is that relatively simple tools can be used to produce slots and grooves. The tool width and geometry are selected for the required feature and successive cuts are used to reach the required depth and form.
Shaping can also be useful for certain keyways and internal features where a suitable reciprocating tool can reach the cutting surface. For repetitive production, however, broaching, slotting or CNC machining may provide a more productive solution.
The adjustable toolhead and table arrangements of a shaping machine allow inclined surfaces and dovetail forms to be produced. This was particularly useful in traditional machine-tool manufacture where slides and guide features required accurately related angular surfaces.
The ability to produce such geometry using a simple single-point cutting tool illustrates an important characteristic of shaping: complex cutter geometry is not always required to generate a geometrically useful surface.
Unlike turning or drilling, where cutting speed is associated directly with continuous tool or workpiece rotation, the cutting speed of a shaper varies during the reciprocating stroke when a mechanical linkage is used.
For process planning, an average cutting speed may be considered from the distance travelled during the cutting stroke and the time taken to complete that stroke:
Vc = L / tc
where consistent units must be used and:
In practice the stroke must normally extend beyond the workpiece sufficiently to provide approach and clearance, so the machine stroke is longer than the surface actually being machined.
Feed in shaping is normally applied incrementally between cutting strokes. For machining a broad flat surface, the feed is generally transverse to the direction of the cutting stroke.
Depth of cut is established by the relative position of the tool and workpiece. As with other single-point machining operations, feed and depth of cut affect cutting forces, material-removal rate, tool life and surface finish.
The interrupted nature of shaping should also be considered. The cutting edge enters the workpiece repeatedly rather than remaining continuously engaged.
The workpiece must be held rigidly enough to resist the forces generated during the cutting stroke. Small components may be held in a machine vice, while larger or irregular workpieces may be clamped directly to the machine table or supported in a suitable fixture.
Workholding should provide adequate support close to the cutting region where practical. Excessive workpiece overhang or inadequate clamping can increase vibration and deflection and reduce machining accuracy.
The capacity of a shaping machine is strongly influenced by its available ram stroke, but stroke length alone does not define the size of component which can be machined. Table dimensions, vertical clearance, tool position, cross travel, workholding and machine power and rigidity must also be considered.
Shaping and planing are related reciprocating machining processes, but the principal cutting motion is arranged differently.
| Shaping | Planing |
|---|---|
| The cutting tool normally reciprocates while the workpiece remains substantially stationary apart from feed movements. | The workpiece normally reciprocates relative to a substantially stationary cutting tool or toolhead. |
| Traditionally suited to smaller and medium-sized workpieces within the capacity of the shaper. | Traditionally suited to large and heavy workpieces which can be secured to the planer table. |
| Normally uses a single cutting tool during an operation. | Planers may be arranged with more than one toolhead to machine multiple surfaces. |
See also: Planing.
Both shaping and milling can produce flat surfaces, slots and a variety of geometrical features, but their cutting actions are fundamentally different.
A shaper normally uses a reciprocating single-point tool and includes a non-cutting return stroke. A milling machine uses a rotating multi-edge cutter and can provide substantially more continuous material removal. This is an important reason why milling displaced shaping for many production applications.
The shaper nevertheless has the advantage that relatively simple single-point tools can be produced for specialised features without requiring a dedicated milling cutter.
| Advantages | Limitations |
|---|---|
| Simple single-point cutting tools | Return stroke does not normally remove material |
| Can produce flats, slots, angular surfaces and forms | Generally lower productivity than modern milling |
| Tool geometry can be produced for specialised features | Component size is limited by machine travel and working envelope |
| Useful access to some slots and internal features | Reciprocating motion limits the practical cutting cycle |
| Mechanically straightforward machining principle | Much less common in modern production environments |
Although shaping machines are now uncommon in high-volume manufacturing, the process remains useful from an engineering point of view. It clearly demonstrates the relationship between cutting motion, feed motion, single-point tool geometry, workholding and machine kinematics.
Older shaping machines also remain in some workshops, training facilities and toolrooms, where they may still provide a practical means of producing flat surfaces, slots or specialised features.
Where a component is to be machined using a shaper, the designer or manufacturing engineer should consider:
The following external resources were included on the original RoyMech page and are retained for additional information relating to shaping machines.