After forging tools such as lathe and planer tools, reheat about 2in. to a cherry-red heat (750° C), dip about lin. in water until cold. Withdraw from the water and polish the cold portions with a piece of emery cloth so that the temper colour may be observed as the heat remaining in the undipped portion of the tool runs up the tool. If the tools are required for cutting hard material, the temper colour should be allowed to run to a light straw (220° C), when the whole tool should be dipped in water, and only removed when cold. For milling cutters, taps, dies, and drills the temper colour should be a dark straw or yellow (245° C).

General Note

Avoid as far as possible having sharp angles in any tools, as these frequently form the starting point for cracks when hardening. Never use quite cold water for hardening ; just take the "Chill" off. See that there is a plentiful supply of water being used, as this ensures a uniform hardness when more than one tool has to be treated. Tools to be hardened at one end only, such as lathe tools, should be kept in motion while in the water, or the hardened portion may break off when put into use. Remember it is very easy to spoil good steel.

To Ensure Accurate Work

If your lathe should not bore straight, level it carefully with a good level. This will entirely overcome the difficulty.

If your lathe should not face straight, it also is merely a matter of levelling.

If your lathe should not turn straight, use the same levelling operation, and then carefully test to see that the centres line up exactly with each other. Remember that if a long piece is turned between centres without steady or follow rest support the work itself will spring away from the tool to some extent.

If your lathe should chatter, it may be due to any one of several causes :-

Improper levelling; correct as above.

All four feet not resting solidly on the floor or on wedges.

Work extending too far from chuck ; change method of chucking or run outer end in steady rest.

Too great a distance between centres without support on slender shaft ; use steady rest.

Inaccurately fitted chuck plate.

Bolts which hold chuck to chuck plate not tight.

End play in the spindle ; adjust by means of the collar and nut on rear end of spindle.

Cross slide not fitting the bridge tightly ; adjust gib.

Compound rest gib loose ; adjust.

Cutting edge of tool below centre.

Dirt between one of the centres and its bushing.

Tool not securely clamped in tool post.

If using a tool holder, the set screw holding the inserted cutter should be tight.

Machine thrown out of balance- by addition of special chucking fixtures ; by work of an irregular shape or weight; or by being speeded too high on some classes of work.

If your lathe should cut a drunken thread, tighten the nut on the tail-stock end of the lead screw, if that nut is too loose. On the other hand, do not make the nut too tight, as it would then be difficult for you to get the sliding tumbler knob into the holes when the lathe is running. The lead screw is always in tension whether you are chasing right-hand or left-hand threads, because the pull is against the outer end of the bearing in either case.

Should you have occasion to remove any of the gears from the reverse plate, be sure, when replacing them, that they are properly located by the dowel pins.

Never leave your lathe with the chuck wrench remaining in the chuck-someone else might start up the lathe. ( The Model Engineer.)