Tag Archives: Lathe

Lathe: Backgear

Beginners are sometimes confused about how to engage backgear – especially if the lathe lacks a handbook – but with a little care anyone can work out how it should be done, at least on a conventional machine. On the main spindle of the lathe, the one carrying the drive pulley, will be found a large gear, generally referred to as the “Bull Wheel”. The Bull Wheel is attached to the pulley by a nut and bolt, a spring-loaded pin, a pawl that presses into a gear on the pulley (or some other means) and, if this fastening is undone – by slackening the nut and pushing it towards the pulley, or by pulling the pin out – it should be found that the pulley will spin freely on the shaft. By moving the “backgears” into position – they generally slide sideways, or are mounted on an eccentric pin – the mechanism will come into operation. If the pulley will not spin on the shaft, or there seems to be no obvious way of disconnecting the Bull Wheel from the pulley, it may be that you are dealing with an “over-engineered” machine where some clever device has been introduced to make life “easy” for the operator. Sometimes there will be a screw, flush with the surface of the drive pulley and beneath this a spring-loaded pin that pushes into the back face of the Bull Wheel. Quick-action “Sliding-cam” mechanisms are occasionally used (as on the Drummond and Myford M Series lathes) where a knob on the face of the Bull Wheel has to be pushed sideways, and so ride up a ramp, which action disengages the connecting pin automatically. Some lathes, with enclosed headstocks (like later Boxford models) have a “single-lever” backgear; in this system moving the first part of the lever’s movement disengages the connection whilst the next brings the backgear into mesh.

Lathe: Lead Screw

The lead screw provides automatic feed and makes thread cutting possible. It is a precision-threaded shaft, driven by gears as the headstock turns. It passes through the front of the carriage apron and is supported at the tailstock end by a bearing bracket.  Controls in the apron engage a lead nut to drive the carriage as the lead screw turns. Continue reading

Lathe: Cross Slide

The cross-slide is mounted to the top of the carriage to provide movement perpendicular to the length of the bed for facing cuts. An additional motion assembly, the compound rest, with an adjustable angle, is often added to the top of the cross slide for angular cuts. The cutting tools that do the actual metal removal during turning are mounted in an adjustable tool holder clamped to the compound rest.

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Lathe: Carriage

The provides mounting and components for tooling. The carriage moves left and right, either through manual operation of a hand wheel, or it can be driven by a . At the of a carriage is a saddle that mates and aligns with the bed ways.

The ‘s cross-slide, compound rest and tool holder are mounted to the top of the carriage. Some carriages are equipped with a rotating to allow a variety of to be used in succession for multi-step operations.

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Lathe: Headstock

  1. The headstock holds the spindle and drive mechanism for turning the work piece. The spindle is a precision shaft and bearing arrangement rotated directly by a motor or through a motor-driven belt. Gears or sliding pulleys mounted at the rear of the headstock allow spindle speed adjustment.

  2. A work piece is held in the spindle for turning or drilling by a jawed chuck or a spring collet system.  Large, unusual shaped, or otherwise difficult to hold pieces, can be attached to the spindle with a face plate, drive dogs and special clamps.
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