valutazioni - 2, GPA: 3.5
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Facilità d'uso
However, the parting tool is a rough cutter, so that ultimately the skew must be used in cleaning the cut. The whole operation can be done with the skew, and this technique is illustrated by the drawings in Figs. 49, 50 and 51. The first movement is a nicking cut with the toe of the skew, as shown in Fig, 49. This cut cannot be made very deep without danger of burning the chisel, so a clearance cut is made by inclining the skew away from the first cut and again pushing the tool into the work. This procedure of side cut and clearance cut is continued as often as needed. The important point to note is that while the skew can be pushed into the wood in any direction, the cutting edge itself must be inclined a little away from this plane, see Fig. 51. Note that if the full cutting edge of skew bears against the cut surface, the tool will have a tendency to run. Now, observe the proper way to make the cut, as shown at left end of Fig. 51. The chisel is pushed straight into the work, but the cutting edge is inclined away from the cut surface - only the extreme toe cuts. This is the most important principle in skew handling, and you wili run into it repeatedly in making shoulders, beads and vee cuts. CUTTING A SHOULDER The parting tool is first used to reduce the wood to within 1/16” of the required shoulder and diameter, as shown in Fig. 52. The waste stock is then cleaned out with the gouge, Fig. 53. Actual cutting of the shoulder is done with the skew, as shown in Fig. 54, and is a duplication of squaring end. The horizontal cut is also made with the skew, but in a little different manner from that used in doing plain cylinder work, if the shoulder is long, the ordinary skew position can be used for the outer portion of the cut, but at the angle between the horizontal and vertical cuts, the heel of the chisel moves into a position tangent between the skew and the cylinder, as shown in Fig. 55. In this position, the handle of the chisel is raised slightly to allow it to cut as the tool moves along the rest. A very light cut should be taken in order to produce smooth work. The heel of the skew can be used for making the entire cut, if desired, but the cut, whether in this position or any other position, should not be picked up directly at the end of the stock. It is quite evident that any horizontal cut started directly from the end of the work will have a tendency to bite into the wood, often ruining the entire piece. Always run off the end and not into it, Where a very short shoulder makes this impossible, it is best to use the skew fiat in a scraping position. If the cutting technique is used, engage only with the heel of skew in a very light cut. Fig. 52 Fig. 53 Fig. 54 17 Fig. 55 CUTTING SMALL BEADS Beads can be scraped or cut. The easy method of scraping is done with the spear chisel, and works to best advantage on beads separated by parting tool cuts, as shown in Fig. 56. Scraping is slower and less productive of clean work than cutting, but it has the advantage of perfect safety - you won’t spoil the work with long gash runs. Cutting beads quickly and accurately with the small skew is one of the most difficult lathe operations. Various working methods can be used, the usual system being as shown in Figs. 57, 58 and 59. The first cut is a vertical incision at the point where the two curved surfaces will eventually come together. This cut can be made with either heel or toe of skew, Fig. 60 showing the toe being used. Now, place the skew at right angles to the work and well up on the cylinder, as shown in Fig. 57. The chisel is flat on its side at the start, and is evenly rotated through the successive stages of the cut, as shown in Figs. 57, 58 and 59. At the same time, the chisel is pulled slightly backwards to maintain the cutting point. The entire cut is made with the heel of chisel. The opposite side of the bead is cut in the same manner, one cut serving to produce the full shape in each instance. Beads cut in this manner are beautifully smooth and polished, and the technique is well worth mastering. Fig. 60 VEE GROOVES Cutting the vee groove demands much the same technique as the bead, except the skew is hinged straight into the work without rotation, as shown in Fig. 61. Only one-haif of the vee is made at a time, and one, two or more cuts may be needed on each side to obtain the desired shape. As in all cutting with the skew, the bevel next to the cut must be used as a fulcrum, without at the same time allowing the full edge of the chisel to catch and cause a run. Vee grooves can also be made with the toe of the skew, in the manner already described for squaring an end. Fig. 61 18 LONG CUTS Long cuts are usually either convex or straight-tapered surfaces. With a convex surface, the method used in making the finishing cut is shown in Fig. 62 and 63. The gouge is turned on the tool rest so that it wiil be inclined considerably in the direction in which it is about to move. The grind i...
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