PI: I (Continued) As the tool lies aDproximatelv 6+ in. to the left of the stvlus point, the template sho~Id be placed between the centres of the support heads a similar distance to the right of the intended position of the finished workpiece. E.g. material - mild steel, cur-ing speed 200 ft. (60 m.) per min. depth of cut is in. (5 mm.), feed rate 0'002 in. (0'05 mm.) per rev. A iT.i.lillmUm number of cuts per component should be taken to minimise tool point wear, thereby maintaining repeat accuracy :hroughout the batch.
Wherever possible, the more robust (a) of the two cutting tools should be used, the lighter tool (b) being reserved for work requiring steep bad~ angles and grinding relids (fig. 9). The hydrau:.:c angle slide should be fed to its extreme inward position by means of u'1e hand control lever. Rotate u1.e cross slide hand wheel in an anti-clockwise direction until the stylus point contacts "L1.e smallest diameter of the template and COIT'Jner:ces actuating the valve controlling the hydraulic slide .. SCREWCUTTlNG (Fig. 7) A higher cutting speed for screw cutting can be achieved by use of the Copying equipment.
Whilst the only purpose of the equipment during screwclltting is the automatic withdrawal of the tool, the man- ual withdrawal speed is usually the factor limiting 11 tP.reading operation, ;;0 the ac.vantage to be gained from using the equipment will be reedEy appreciated. Tl1e most satisfactory results are obtainec. on fine threaded work and with the more free cutting materialS, e.g. brass, cast iron, etc. With a tool overhang of approximately I in. position the rear tool slide to ensure thaI the tool is clear of the largest diameter of the workDiece blank.
Care should be taken to ensure that th.e tool is set exacrIv to centre height otherwise discrepancies will occur eSDeciailv on s;r{all diameter work. " - Copy turning can now commence, the depth of cuts for the 'first off' only being set by the rear tool slide handwheeL For cutting right-hand threads the tool should be in an inverted position, the direction of rotation of the headstock spindle therefore being in an anti-clockwise direction when viewed from the tailstock end of the lathe.
On completion of the first workpiece, withdraw t..;"e hydraulic slide by means of the hand control lever and, only if more than one cut is necessary, traverse the whole slide assembly away from the work by means of the cross slide handwhee1 a distance equal to the depth of profile; on subsequent workpieces the cuts should be applied by this hand wheel. The setting of the rear tool slide should not be altered after compietion of the 'first off'unless a uniform fine finishing cut over the entire profile of the workpiece is required. For cutting left-hand threads the tool should be in the normal upright position, the direction of rotation of the headstock spindle being in a clockwise direction.
The template required should have a single shoulder of sufficient depth to allow ui.e tool to be automatically withdrawn from the work. The stylus point must always be clear of the template diameter contacting only the shoulder at point of withdrawal. If more than one cut is necessary, then these should be applied by the cross slide handwhee1. The micrometer saddle stop supplied with the lathe can be set towards the tailstock to position carriage after completion of each cut.
The cur-Ling speed, depth of cut and feed rate are, as in normal turning, dependent upon the material, but accepted practice using carbide tipped tools is to combine high cutting speed with a fine feed to obtain the best surface finish. Taper screwcutting can be carried out to advantage (the above remarks regarding fine threads or free cutting materials again applicable), but the 'setting-up' differs slightly from that of parallel screwcutting. A template is required having a taper similar to that of the taper thread being produced, the stylUS point contacting this 23 ,