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Work continues with emery 1m whose grains are comparable to those carbo 100 or 120 , but that leaves less deep fractures because of its lower hardness . Now we will adopt general way for the rest of the work, a normal stroke on which it must attract the attention specially: they consist a back and forth roughly centers (Fig 22 and 23), the total amplitude is about 1/3 of the disk diameters (therefore it is necessary to exceed one sixth of each side , 3 to 4 centimeters with a mirror of 20 centimeters), with a lateral departure constantly variable limit 1/8 at the each side.   the shape of the strokes may well affect that of a V or W or of a loop more complicated ∞ as an example ( G. W. Ritchey ) . Every five or six strokes it turns a little the upper disk in his hands and one turns oneself as in  roughing(coarse grinding) . What is essential in all this is only to respect roughly 1/3 the average amplitude and to vary as most possible

The gap of sphericity can exceed 2/10 of a millimeter on a mirror of 20 centimeters, it must be remembered has complete roughing by a slower method but catching this defect. It's not difficult, just keep working with racing roughly CENTERED as in Figure 18 B, but with a total range of motion not exceeding this time disk diameter of half

To deepen the mirror ( hogging out ) fastest way: the mirror of the center can go with safety until 1 or 2 centimeters edge of the tool and the straight runs being managed along chords may have ten centimeters with glasses of 20 centimeters diameter ; a little bit of experience indicate the non-hazardous limit for tilting the mirror on the edge of the tool. One can be five to ten straight races on site, then one rotates a fraction of turn the mirror in the hands and it resumes work in a direction slightly different , move around the post. If the post(stand) allows full rotation of the operator, the tool can remain stationary ; otherwise it is necessary to turn the timely manner a user also all its periphery. We see in Figure 18A, the figure described by the mirror of the center during this work