Holder

thicknesses are to be ground by the latter method, on wheels of two different diameters, six sets of templates will be required to meet all eventualities.

Moreover, when a large grinding wheel of say 12-in. diam. is employed, the curvatures formed on the faces of the tool will be nearly linear, but with a small wheel of only 3 or 4 in. diam., the concavities ground may seriously undermine and weaken the extreme cutting edges of the tool.

It should be emphasised that the grinding operation will be greatly facilitated if ground, square section, highspeed steel is used for making tiie lathe tools, for this material will lie flat and without rocking on the grinding table, and will thus enable the required angles to be accurately ground.

When the rest has been set, the tool is applied to the wheel with a sliding motion, and this movement must be maintained throughout, so that fresh surfaces are constantly brought to bear on the wheel, and the risk of overheating the steel is thus reduced. If the tool is allowed to dwell or is forced against the wheel, heating will arise which may spoil the tool's temper and cutting properties. On no account should the tool be dipped in water to accelerate cooling, for the subsequent evaporation of the water during grinding may cause surface cracks to form at the cutting edge.

When the cutting edges have been satisfactorily formed on the coarse wheel, the work is transferred to the fine or finishing wheel, and if, as already explained, the grinding rest is set to form a slightly smaller clearance angle, it will be found that but little further grinding is required to impart a good finish to the cutting edge, and at the same time there is very little risk of overheating the tool.

Stoning the Tool. On completion of the grinding operations, the final finish is given to the cutting edges of the tool on the oilstone. If free-hand stoning is employed, great care must be taken to avoid rounding the tool's edges and thereby reducing their clearance angles.

With this possibility in view, it is better, whenever possible, to use a stoning jig of the pattern described in the previous chapter, and if the tool has been ground in the manner indicated, it can usually be resharpened several times on the oilstone before regrinding becomes necessary.

It is essential that a hard stone, such as an Arkansas oilstone, should be used for this purpose, for if the tool cuts into and grooves the surface of the stone, a rounded or even a blunted cutting edge may result. Light pressure only should be applied when honing and the stone should be kept clean and well lubricated.

Hand-turning Tools. Before leaving the subject of sharpening lathe tools, two tools commonly used in hand turning should be mentioned, namely the graver and the thread-chasing tool.

The Graver. When mounted in a wooden handle and supported on the handrest, the graver, illustrated in Fig. 23, is used for a great variety of hand-turning operations.

Fig. 24.

As will be seen, the point is ground at an angle of 45 deg. to the long axis of the tool to form a lozenge-shaped facet, thus forming two cutting edges at the sides of the pointed tip. The tool is best ground by supporting it in a V-block 011 the table of the angular grinding rest, which is tilted to form an angle of 45 deg. with the side-face of the grinding wheel. The sides of the tool should on no account be ground, and great care must be exercised when grinding not to overheat and soften the slender tip.

After grinding, the flat area at the tip should be honed to a highly finished surface on the oilstone, and for this purpose, the use of a stoning jig will be found a great advantage.

A convenient form of stoning jig is illustrated in Fig. 24, but the jig described for stoning plane irons in the previous chapter can also be used, if a recess to receive the shank of the graver is filed in tht surface of the clamping piece.

When the surface of the lozenge-shaped facet has been accurately honed, the sharpening operation is completed by applying the sides of the graver flat to the stone, and with a few light, well controlled strokes removing any burrs that may have been formed at the cutting edges.

Hand Chasers. Chasers are essentially form-tools and may be used, when mounted in a wooden handle and supported on the hand rest, to give the correct form and final fit to threads screwcut in the lathe. It will usually be found that the upper surface of the tool is flat and in direct continuation of the shank of the chaser. This indicates that, in order to preserve it as a form-tool, the upper surface must be ground or stoned in precisely this manner, otherwise the shape of the cutting teeth will be altered and the tool will no longer serve its intended purpose.

When grinding is required, the upper surface of the end portion of the tool is applied to the side of the wheel, after which the chaser is laid flat on the oilstone and is then moved backwards and forwards in the direction of its long axis, after the manner of stoning the back of a wood chisel.

On no account must the front face of the chaser be allowed to come in contact with the grinding wheel, or the tool will be spoilt for the purpose of thread finishing.

Fig. 25

The ordinary form of hand-chaser designed for external work is depicted in Fig. 25, and for internal chasing the teeth are cut on the side of the tool which is then akin in form to a boring tool.

At this point, an unusual method of grinding an external chaser to serve a special purpose might, perhaps, be mentioned.

When some ribbed tread-plate was required for the cabin floor of a model steam-roller under construction, an |-in. pitch chaser was ground on its end face, with a clearance angle of 10 deg., until the teeth were almost obliterated and only the shallow hollows between the teeth remained. This tool was then mounted in the shaping machine, and a strip of tread-plate with raised ribs was machined equal to the breadth of the ch ^ser.

The work was then traversed for a distance equal to the number of the teeth of the chaser by means of the pitch feed screw, and the process was continued until the full width of the plate had been machined. The result of this improvised operation was most satisfactory and the appearance fully realistic.

In this short review of the subject of sharpening lathe tools, attention has been paid rather to the general principles involved than to listing the many varieties of tools, and the cutting angles recommended, for turning the numerous materials commonly used in the workshop.

In general, these angles are not critical except, perhaps, where maximum output is required ; and satisfactory work should result if the tool is given sufficient clearance to prevent rubbing ; adequate rake to promote free-cutting ; relief to prevent too large an area of contact with the work ; and a form to provide proper support for the cutting edges.

Lathe tools can readily be endowed with all these qualities by adopting the methods of sharpening described.

Finally, it is necessary to emphasise that turning tools should always be kept really sharp, that is to say in the sense that a knife capable of free-cutting is said to be sharp.

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Woodworking Tools and Installation Tips

Woodworking Tools and Installation Tips

There are a lot of things that either needs to be repaired, or put together when youre a homeowner. If youre a new homeowner, and have just gotten out of apartment style living, you might want to take this list with you to the hardware store. From remolding jobs to putting together furniture you can use these 5 power tools to get your stuff together. Dont forget too that youll need a few extra tools for other jobs around the house.

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