Taper Turning on Conventional Lathe MachineTaper turning on conventional lathes can be done via the following methods:Compound (Rest) Slide Method Tailstock offset (set-over) MethodUse of taper attachment1. Compound (Rest) Slide Method Features:Applicable for turning short, steep-angled tapers (normally with degree setting ranging from 10to 890incremental by 10)The compound rest is swiveled (set) to the required angle of taper referred to the lathe’s spindle axisTool feed is done via the compound slide handwheel, hence tool feed by power means is not applicable
1A. Determining Degree setting on compound rest1.Given end diameters D, dand length of taper TLDegree setting,ϴ=tan−1(D−d2TL)2.Given tpi,(taper per inch) Degree setting,ϴ=tan−1(tpi2)3.Given tpf ,(taper per foot)Degree setting,ϴ=tan−1(tpf24)4.Given degree of taper with reference to an axis perpendicular to the works axis ofrotation:Degree setting,ϴ=900−β;where β= the given angle;5.Given included angle of taper:Degree setting,ϴ=12x givenincluded angleᶿdDTL
2.Tailstock Offset (Set-over) MethodFeatures:Applicable to comparatively long, gradual tapers;Workpiece is held between centers; being out of alignment, center holes are likely to wear out of their true positions if the lathe centers are offset too far, causing poorresults and possible damage to centers.Tool feed by power means is available.Determining Amount of Tailstock Offset The most critical operation in taper turning by the offset tailstock method is determining the proper distance the tailstock should be moved over to obtain a given taper. Two factors affect the amount the tailstock is offset: the taper desired and the length of the workpiece. If the offset remains constant, workplaces of different lengths, or with different depth center holes, will be machined with different tapers as shown illustrated belowEffect of fixed amount of set-over with different lengths of workpieces.1. Given over-all length of workpiece OL, length of tapered portion TL, large end diameter of taper Dand small end diameter d;Offset=OL(D−d2Tl)
2. Given taper per inch tpior taper per foot tpfand overall length of workpieceOL;Offset=OL(tpi2)=OL(tpf24)3. For Metric tapers:Metric tapers are expressed as a ratio of 1 mm per unit of length. If the small diameter (d), the unit length of taper (k), and the total length of taper (TL) are known, then the large diameter (D) may be calculated. The large diameter (D) will be equal to the small diameter plus the amount of taper. The total amount of taper will be the taper per millimeter (l/k) multiplied by the total length of taper (TL).D=d+TLkThen, the amount of tailstock offset can be calculated as follows:Offset=OL(D−d2Tl)Example 1. A portion of a piecepart having an overall length of 150mm is tapered to a length of 60mm, the small end diameter being 10mm. If a taper ratio of 1:30 is applied, determine the amount of tailstock offset to taper-turn the part.