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.
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
The lathe is a machine tool used in metal cutting operations called “turning.” The work piece is rotated as tooling is applied to it to remove material. Lathes can be manually operated or operated by computer numerical control (CNC). In either case, the basic parts are similar.