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Title: |
1895 Article-P. Pryibil, Twist Machine |
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Source: |
Modern Mechanism 1895 pgs 113-114 |
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Insert Date: |
6/8/2011 2:19:36 PM |
The Pryibil Twist-Machine, shown in Fig. 1. is a recent production for making all kinds of spiral or rope moldings, either straight, tapered, curved, or so called oval. It will make right, left, or pineapple cuts, and will also do straight fluting: and a further extension of its range is in its capacity to cut from one to six threads on a piece, and to make any degree of twist, from one turn in 1½ in. to one in 10½ in. of length. The cutters which it employs are similar in shape and arrangement to those used on variety shapers and are held between collars; but they are so arranged that the knives have a peculiar action, cutting from outside in. Whether the twist is right or left handed, the cutters rotate in the same direction. At starting upon its design the makers considered the fact that machines having solid cutter-heads and using knives formed to outline, like those on straight molding-machines, cut across the work at the angle of twist, and. by cutting one side of the body against the grain, were apt to make rough work. In avoiding this, machines having two cutter-heads and two sets of knives, placed close together and turning in opposite directions, have been used; but this requires the employment of two sets of spindles, pulleys, bearings, belts, etc.; of course, more than doubling the care required to effect adjustment. In addition to this there are required two separate and complete sets of cutters where right and left twists are required; and, as each set comprises four slotted and formed knives, the expense is considerable in this direction alone. But it is in the substitution of one set for another, and the difficult setting of all of them to match, that the principal disadvantage of the two-cutter system lies; besides which there is an additional trouble in the difficulty and danger of running two sets of knives side bv side at 5,000 turns per minute, close enough together to have their cuts meet, yet without the cutters themselves touching each other. This makes the double fly-cutter undesirable, particularly where work in great variety and quantity has to be turned out at a low price. The end-cutter, or boring-cutter, is another class of machine originally devised to produce smooth work; there being a single knife at the end of a spindle that is set square with the work, and which at the beginning of the cut is fed endwise, causing the cutter to bore to proper depth, after which it cuts sidewise. In this class of machine there are required both right and left hand knives, as with the double-fly cutter, and both they and the belt must be changed to suit right and left hand twists. There being but limited space between the two bodies on a piece of twist work, there is room for only one knife, and. as this can not be set at such an angle as to cut properly, it practically scrapes its way through the stock—a slow operation, calling for very frequent resharpening of the cutting-tool. The Pryibil machine uses both classes of cutters, the boring and the scraping tools, but the former are used only in that class of double spiral work where there is a space between two separate and disconnected spirals, each one twisted around the other, but not touching it. Ply-cutters can not do such work as this, but can do every other class of work. They have been made to do square work by setting them sidewise to their collars at an angle of 45°, causing them to cut with a shearing action from the outside of the work toward the center. As the knives are made from bar-steel, and are straight-faced and right and left, the two of a pair can be placed together face to face to compare their outline in grinding. By this system the difficulty is much reduced of cutting the two sides of the body to match at the top; but still further accuracy in this particular is got by an adjustment to the machine by which the work may be swung around to match the cutter in a moment without stopping the cutter. The same movement enables double and Flo. «.-Eg«n ou-ved-moldlng machine.
curved tapers—that is, tapers that are large in the middle and small at both ends—to be made by the use of suitable wooden forms. This machine is particularly well adapted to making screen-work of the "Moorish" pattern, consisting of long, thin spirals interwoven
like wire-netting. Such work is ordinarily considered very difficult to make, by reason of the trouble in getting the thin sticks to stand up against the cut. In the subject of this illustration there is a steadv rest directly opposite the cutter, holding a wooden block, through which a hole is bored, fitting the stick to be cut spiral. The cutter works its own way through the block to the work, and, as the cutter and the block maintain their relative position while the work feeds along, the latter can not spring or break. The spindle-frame of this machine is counterbalanced so as to swing easily from right to left, and is fed to the work by a quick lever-motion. Changes of twist are produced by turning two wheels on a screw, according to a table attached to the machine; the change from right to left is effected by placing the gears on one or the other side of a rack. |
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