Fox of Derby: Lathe in Birmingham
Note: This is a sub-section of Fox of Derby
See photographs. This is described as 'c.1820', and it came from an 1817 machine shop at Milford Mill, Derbyshire.
It is now in store in the Birmingham Museums and Art Gallery Collections Centre, having been removed from the former Birmingham Science Museum.
W Steeds' 'A History of Machine Tools 1700 - 1910' includes photographs and information on the lathe. It is larger than the lathe at Wortley Top Forge, having a much longer bed, but the design is very similar, except for the lack of a leadscrew for screwcutting.
The lathe was 'officially' dated at 1817, although Steeds was 'inclined to put it five to ten years later'. The lathe also features in L. T. C. Rolt's 'Tools for the Job', and it is interesting to note that, like the Wortley lathe and the Birmingham museum planer and London Science Museum's slotter, it came from Strutt's ground-breaking workshop at Milford Mill. Rolt says: '… they were used in the construction and maintenance of textile machinery. They were driven by waterwheel and as the date 1817 appears on the cast-iron beams and line-shafting brackets of the building that was evidently built to house them, it is reasonable to ascribe them to this year. The machines have been attributed to William Strutt, but while Strutt was a most ingenious engineer and was undoubtedly responsible for the Milford building, the advanced and masterly design of the tools clearly reveals the hand of Fox'.
The acheivement of James Fox in identifying key aspects of lathe design, which we now take for granted, cannot be overstated. His appreciation of the the important design criteria and the quality of his detail design and the quality of construction are remarkable for the time.
Details
In photo 3, the ratchet handle and small wheel (bottom left) were connected to a small chain which moved the drive belt between the fast and loose pulleys on the overhead lineshaft, in order to start and stop the lathe. A great deal of effort went into making the cast iron bracket for this lever, and bedding it to the shape of the lathe's bed and leg. The bracket is also visible in photo 13. The horizontal rod at the bottom of photo 3 moves a lever to operate the reversing bevel gear cluster seen in photo 4. The bevel gears turn the square layshaft which drive the worm and wheel to move the lathe's carriage.
In photo 6, the two brackets projecting from the headstock are used to support the shaft with six pulleys and two gears seen in photo 7. The two gears slide on 'feathers' (long keys which are a sliding fit in the gears). One pair or the other will be engaged to provide high or low ratios, giving 12 spindle speeds.
Photo 8 shows the carriage (saddle) and toolpost, and the large wormwheel which turns a pinion engaging with the cast iron rack to traverse the carriage. An important feature of the carriage is the extent to which the 'wings' extend forward, providing excellent support when the toolpost is close up to the headstock (the slideways for the carriage extend all the way to the end of the bed). Also note the cut-outs near the ends of the 'wings'. These were provided to accommodate a plate, enabling to carriage to be used as a boring table.
Photo 9: The worm travels with the carriage. To disengage to drive from the carriage, the large lever seen in photo 8 throws the wheel forward out of engagement. Alternatively the square layshaft can be stopped or reversed by the bevel gear cluster at the headstock end.
Photo 10: The design flair and the fine workmanship are evident in every detail of the toolpost.
Photo 12: The design of the tailstock is generally well thought out. It can be moved along the bed by a hand-cranked pinion. Provision is made for offsetting the centre for taper turning. The only shortcoming is that the barrel can only be moved forward by the forcing screw, and has to be pushed back after releasing the screw.
Photo 13 shows the steps taken to ensure that the cast iron bed was rigid, without incurring excessive weight.
Photo 16: Fine work by the blacksmith: the square part of the layshaft was forged and filed, not machined.
The design of a lathe's spindle, bearings, and headstock are critical to the accuracy and finish of work that can be produced. Fox's approach is impressive and intriguing. As described by Holtzapffel:-
The mandrel fig. 85, [Photo 17] was invented by the late Mr. Fox of Derby and is favorably known; the construction appears to have arisen from the idea of a rod supported between centers, modified to expose the one extremity for the reception of the chucks. The shaded conical steel collars are permanently fixed in the cast iron headstock, the mandrel has the screw and shoulder for the chucks, then a large cone which fits the front collar, followed by a cylindrical portion to receive the driving wheels, and then a smaller cylindrical part upon which a loose steel cone is fitted, standing the reverse way to the former. The loose cone is keyed to the mandrel and revolves with it, it is adjusted by a double nut behind, which places the two cones at the distance required by the conical collars and prevents end play, and last of all, there is the tail pin [see below] as before. This, is still more necessary than in the previous example having cylindrical bearings, for in addition to receiving the endlong thrust in turning, it now also prevents the front cone from being jammed into its seat. The cone acting as a wedge, both increases the endway pressure, and squeezes out the oil that should remain between the mandrel and the collars for lubrication, and without the tail pin, their surfaces are exposed to the risk of heating and deterioration from the friction. The adjustment of the tail pin in all cases should be only just sufficient to avoid undue friction in the collars, at the same time it should leave the mandrel under their guidance.[1]
The intriguing aspect of this is, how was adequate lubrication assured? There is no provision for routine oiling of the bearings. The bearings were steel, and the spindle would be either steel or wrought iron, a combination not ideally suited to poor lubrication. It may have been necessary to regularly slacken off the nuts, pull the spindle back, and squirt oil into the bearings, but this would be inconvenient, especially with the need to use pin spanners to adjust the nuts.
The tail pin referred to above is the back stop which bears on the back end of the spindle. Many lathes had a single tapered bearing at the chuck end, and a conical tail pin the support the back end and to take the thrust load. With Fox's arrangement the tail pin has no support function, and serves to adjust and maintain the small clearance in the two tapered journal bearings. Some French drawings show a conical tail pin on Fox lathes, but in fact it was probably flat. Photo 6 shows the tail pin (RHS of picture).
See Also
Sources of Information
- ↑ 'Turning And Mechanical Manipulation' Vol 1, by Charles Holtzapffel, 1856