WORKSHOP HINTS AND TIPS OFF CUT COMPONENT I Setting-up for

second operations SMOOTH THREADED

HEsolution to many problems screwcutting, or with a die in the of setting up for second tailstock dieholder. I do not advise a operations is to use hand holder, unless you use it very T carefully with support from a pad which can be machined in the centre in the tailstock, for a cranked chuck or run between centres with or wobbling thread may not provide MPLNDRE the components mounted on them. an accurate mounting, even if you Concentricity and squareness are force the component up to a true thus ensured for components which shoulder on the . have been partly machined and A component with a thread on an then have had to be removed from outside diameter must be mounted by a mandrel which has an accurate the chuck for the reverse sides to internal thread. Diagram B2 shows be finished. the set-up. Face the material for this n TAPPED If a component is machined with a mandrel, centre with a. centre smooth bore in the first operation, from the tailstock, and drill to size you can mount it by this bore on a for tapping. You can perfom this mandrel for subsequent operations. last operation with the tap supported At the finish, you will be certain that by the tailstock centre, which must be all the diameters are concentric and pointed or hollow, depending on all the faces . There will be no whether the shank of the tap has a eccentricity or sideways wobble to countersink or a point at its end.Take cause trouble when the component is care to keep the tap supported all the assembled with others. time that it is cutting; apply oil to it, and turn it carefully back to clear By GEOMETER swarf if it sticks. Extra grip to drive a component on With light cuts from a sharp tool a stub mandrel can be provided which is set exactly at centre height, through a nut at the end, as illustrated you will find that friction drive is at C. This is advisable for sufficient for a small, smooth-bored a component of substantial diameter, component which is forced firmly on otherwise you may find that a dig-in a mandrel. In making, the mandrel by the tool stops the component with should be turned smoothly almost to the mandrel spinning in its bore. size. Then you can reduce it carefully If you have to turn the outside of a with a file and emerycloth until the large spoked wheel, I suggest that you component can be twisted on firmly. employ the type of mandrel which I On occasion, a component can be have shown at D. As it must project smeared with oil in the bore (to some distance from the chuck, you prevent scoring) and still hold. should centre-drill the end for support An off-cut, or the short remaining by the tailstock. Drill and tap two piece of a used-up bar of mild steel, holes in the larger diameter near the is suitable for a stub mandrel for the chuck to attach the driving bar and three-jaw chuck. The scrapbox in most packing by setscrews. workshops contains a variety of such To set up a taper-bored component, pieces. Select one which is long as at E, a mandrel must be turned with enough to go well into the jaws of the a corresponding taper and provided chuck. Then the set-up will be as with a nut. Fit the two tapers by shown at A. If you are likely to use carefully filing the mandrel, using a the mandrel on future occasions, you smooth file, or preferably a Swiss. should mark it lightly with a centre You can see where to file from marks punch in line with No 1 jaw. left on the mandrel by trying the When a component has a threaded component. Centre-drill this mandrel, bore, which has been tapped or too, for support by the tailstock. screwcut at the first set-up, you can Points in centre are illus- mount it by the bore on the second trated at F. As a centre forms a F occasion, using a threaded mandrel. bearing, the conical part should be An example of this type of mandrel is fairly deep. The tailstock centre 0 illustrated at Bl. When you have must clear, and so if your centre drill chucked the material, turn it to size, is stumpy follow it with an ordinary undercut it, and then thread it, by drill. 31 MAY 1962 673 MODE L ENGINEER