. Model making; including workshop practice, design and construction of models, a practical treatise for the amateur and professional . t, is to see that there is a cone pulleyon the lathe. At least two steps and preferably threeshould be demanded, as the only practicable method ofchanging speed, and at the same time producing the cor-responding change in potver delivered at the ivorh, is bymeans of the cone pulley. The one exception to this state- 28 Model Engineering ment is fomid in the case of the expensive, direct-con-nected, motor-driven lathes. The popular idea that avariable
. Model making; including workshop practice, design and construction of models, a practical treatise for the amateur and professional . t, is to see that there is a cone pulleyon the lathe. At least two steps and preferably threeshould be demanded, as the only practicable method ofchanging speed, and at the same time producing the cor-responding change in potver delivered at the ivorh, is bymeans of the cone pulley. The one exception to this state- 28 Model Engineering ment is fomid in the case of the expensive, direct-con-nected, motor-driven lathes. The popular idea that avariable-speed electric motor can be belted direct to thelathe pulley and a satisfactory adjustment of speed andpower obtained is a fallacy, as the variations in motorspeed produce a corresponding variation in power deliv-ered at the work. The proper way to belt a motor directto a lathe of this kind is by means of a cone pulley on themotor as well as on the lathe. By this means, whengreater power is required at ^the work, the small pulleyon the motor will revolve at high (proper) speed whilethe large pulley on the lathe will take all of tl\,e power. Fig. 10—Centering a Steel rod possible from the belt owing to the far greater tractivesurface presented to the belt by the large pulley. Other considerations are of lesser importance, butamong them may be noted the size of the live spindle,which should be as large as practicable to afford stiffness,the proportions of the nose (threaded portion of spindle),which should have plenty of metal under the threads, andthe size of the hole in the spindle. The bed of the lathe should by all means be machined(milled). Some very cheap lathes are turned out forwood turning with the beds simply cleaned up on agrinder, and these are an abomination. The tailstock (opposite the headstock) should be ad-justable along the bed by means of a screw clamp readily Lathes and Lathe Work 29 accessible, for this adjustment is made hundreds of timesduring the course
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