The following points highlight the various types of attachments used on turret lathes. The types are: 1. Bar Stops 2. Roller Box Turning Attachments 3. Knee-Turning Tool 4. Combined Boring, Turning and Facing Tools Attachment 5. Tooling for Drilling, Reaming and Boring 6. Facing and Recessing Tool Slide 7. Roller Reset Taper Attachment 8. Screw Cutting Self-Opening Die Heads and Few Others.
Type # 1. Bar Stops:
When the work is produced from a bar fed through the spindle a stop is held in the turret and the bar is brought forward to a fixed position to locate the bar end against the bar stop. This ensures that the amount of stock projecting from the spindle is constant for every component and if all the tools are fed with reference stops, they will produce uniform components. These stops usually consist of the adjustable type.
Type # 2. Roller Box Turning Attachments:
Roller box turning tools are generally used for turning any appreciable length on the bar. It consists of a cutter (tool) and a work support (two adjustable rollers), all combined as an integral unit. The support may be in the form of Solid-V or rollers, but rollers are invariably used.
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Fig. 32.10 given below shows a roller box turning tool. Support rollers may either lead or trail the cutting tool and these avoid the deflection of work piece. When the work has been machined previously, then rollers are used leading the tool so that concentricity is maintained. When the roller trails the tools this often brings about an improvement in surface finish due to burnishing action between roller and machined surface.
The main advantage of using this tool is that even for large reductions in diameter, a well-finished surface within close limits of accuracy can be achieved.
V-steadies are also used in place of roller steady support. It is preferred for machining brass and other free- cutting materials. It may also be used for machining two diameters simultaneously.
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Star turning tool holder is used for turning short lengths to prepare the work for use with a roller steady turning holder. Work is supported on a centre which slides along a spring loaded shank as the turret moves forward. In order to neutralise cutting forces, two cutting tools are used in diametrically opposite position.
Type # 3. Knee-Turning Tool:
A knee-turning tool is used on turret for combined boring and tuning operation and for large- diameter work piece. Fig. 32.11 shows how the combined turning and boring operation is performed on the turret lathe.
There is a hole on top, housing a guide bush, in this attachment, in which pilot-bar comes in from headstock and thus giving rigidity and better support to the tool during cutting operation. In this way overhang of tool holder is taken care of.
Type # 4. Combined Boring, Turning and Facing Tools Attachment:
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It is somewhat like a knee turning tool with the difference that it is a larger unit. Normally, four tools can be mounted one for boring, one for facing and the remaining two for turning which can be set to the work one after the other or simultaneously on different diameters.
Type # 5. Tooling for Drilling, Reaming and Boring:
Drill chuck is attached to and operated from the turret. Start-drilling tool holder is used to prepare the work for drilling. This type of tool holder is also provided with a pair of cutters to enable operations like facing and chamfering.
Reamer is generally mounted in a special floating adaptor so that reamer may centralise itself in the hole. Boring is also performed from the turret using boring bars employing single or multiple tools.
Type # 6. Facing and Recessing Tool Slide:
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Most of the facing work is done from the cross-slide using standard tools, but on occasions it may be necessary to work from the turret. In such cases, a straight edge tool, with its edge set up perpendicular to the axis and held in knee tool holder is used.
Recessing can be done more conveniently by a special attachment called recessing tool slide. An operating handle actuates the slide by means of a rack and pinion, and stops are provided to control the diameter of the recess A typical recessing tool slide is shown in Fig. 32.13.
Type # 7. Roller Reset Taper Attachment:
This attachment is used for taper turning operation on the turret lathe. It consists of tapered guide bar mounted over the work in the same direction as pilot bar. The tool holder resembles the bar turner and can be easily adjusted for size by means of a graduated dial. The tool and the rollers recede as they progress along the work, guided by the bar, thus producing the desired taper.
Type # 8. Screw Cutting Self-Opening Die Heads:
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When a required length of the job is to be threaded, this attachment is used. When the job has been threaded, the feeding of turret head is stopped and the die opens instantaneously to clear the thread portion of the job while returning back with turret head. Commercially it is available in various types and sizes.
Type # 9. Collapsing Tap:
It is used for cutting internal threads. Its most important feature is that blades are caused to collapse into the body of tap, when threading is completed.
