In making, say, a roller about 0 in. in diameter by 50 in. long, threaded with sixteen threads in 9 in. half-way round the roller, its other half having a straight thread, proceed as follows. First make a plain pattern of one-half the roller from which to obtain four castings. Allow for metal to turn off the threads and for facing at the .joint. Two half castings being faced and fastened together, the parallel rings may be turned out. The other two halves being attached to each other, a double thread (a single one would not answer) may be cut. Each roller is now divided, one-half of each taken, and the pair dowelled together to form a pattern. The turner should leave a taper in each ring to enable the pattern to be easily drawn from the sand. The halt' pattern with the parallel rings is lifted straight from the sand; the other half is withdrawn by screwing out of the sand. As this causes the pattern to move endways in the mould, the latter must be mended afterwards, or, better, the plain neck at one end (it there is one) should be attached loosely so that it may be withdrawn first; the end motion then carries the pattern into the space left.

A few rollers only may be built up of turned pieces in the manner described, a neck being arranged with collar at, each end for holding the parts together. A cast screw is likely to cause trouble if required to actuate a nut. The rollers could be made of hard wood, but a special tool would be wanted for the screw-cutting lathe. Any jobbing iron-founder would make the castings if supplied with the pattern. In turning the pattern, consider the shrinking of the metal during casting, double contraction being allowed for the plain half roller.