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presuming you mean the lead screw on a lathe, used when cutting threads on the workpiece, then the screw itself is obviously fixed, but the rotation of it may be able to be changed, depending on the lathe manufacturer.
Pitch measurement refers to the distance from one thread to the next when threads are cut on a lathe. Different threads have different pitches and a lathe can be set to to cut to any specified pitch. This is achieved by selecting the pitch and engaging the lead screw on levers located on the headstock, then engaging the half-nut around the lead screw from the apron. With the correct threading tool inserted threads can be cut into the workpiece.
The lead screw moves the turret by a precise increment for every rotation of the screw. This allows the machine to generate threads in a workpiece, to generate precise length and diameter dimensions, and to maintain a constant rate of metal removal.
what is a leadscrew
the leadscrew is used for thread cutting on a lathe
By hand. You can achieve incredible accuracy by hand, it just takes forever. Also lead screws made on the new lathe will be better than the hand filed one and so on...
sliding pair
A half nut is literally a nut split in half, length wise and makes up the basic half-nut mechanism. Such a mechanism is typically found on a engine lathe. This mechanism can be "open" or "closed" and when closed clamps onto the lead screw of said lathe. This forms a connection between the apron of the lathe sliding on the ways. The apron carries the cross and compound slides, the latter in turn holds the cutting tool. When closed, or "engaged", the movement of the apron moves relative to the rotation of the lead screw. This lead screw is precise in nature and can be described in terms of threads per inch (or per meter or millimeter in case of metric). The lead screw is also connected somehow (there are various methods) to the main motor of the lathe and this ratio of gears can be changed so that many variations of threading, all relative to the thread of the lead screw, can be accomplished on the workpiece being turned/threaded by the screw cutting operation. On a basic older style lathe, the screw begin cut can not be cut in a single pass of the cutting tool. This means that the half-nut may need to be disengaged to reverse the direction of the apron allowing for the cutting operation to be repeated, each time engaging and re-engaging the half nut, until the depth of the screw being cut has reached a final thread depth.
A half nut is literally a nut split in half, length wise and makes up the basic half-nut mechanism. Such a mechanism is typically found on a engine lathe. This mechanism can be "open" or "closed" and when closed clamps onto the lead screw of said lathe. This forms a connection between the apron of the lathe sliding on the ways. The apron carries the cross and compound slides, the latter in turn holds the cutting tool. When closed, or "engaged", the movement of the apron moves relative to the rotation of the lead screw. This lead screw is precise in nature and can be described in terms of threads per inch (or per meter or millimeter in case of metric). The lead screw is also connected somehow (there are various methods) to the main motor of the lathe and this ratio of gears can be changed so that many variations of threading, all relative to the thread of the lead screw, can be accomplished on the workpiece being turned/threaded by the screw cutting operation. On a basic older style lathe, the screw begin cut can not be cut in a single pass of the cutting tool. This means that the half-nut may need to be disengaged to reverse the direction of the apron allowing for the cutting operation to be repeated, each time engaging and re-engaging the half nut, until the depth of the screw being cut has reached a final thread depth.
Lead screws (always pronounced "LEED," as in the present tense of the verb "to lead") are used in mechanical transmission systems to convert rotary motion to controlled linear motion. A common example is in the machinist's screw-cutting lathe. Here a motor turns the lathe's headstock to rotate the piece being machined. A train of gears connected to the headstock turns the lead screw which is usually as long as the entire lathe. As the lead screw turns it propels the cutting tool along the workpiece at a rate directly linked to the rotation of the headstock.
Yes very dangerous, can contain lead and asbestos.