|
The Mk. 3 Model TB was very similar in general arrangement to the Mk. 1, but with a significant number of general improvements.
The bed was of V, rather than flat section, and arranged along the lines of some models of the American LeBlond lathe, with the front V constructed so the the main load-bearing and wearing surface was made very wide and presented at a shallow angle, whilst the inside of the same V was made both steeper and shorter. A better range of bed lengths was also offered, from 10 feet in foot intervals up to 22 feet - at which point the between centres' capacity was 17 feet and 6 inches - and the bed had 5 support legs. The gap could be ordered in two versions, single and double. The single gap allowed material up to 46 inches in diameter and 11.5 inches deep to be turned whilst the optional "double gap" increased the depth capacity to 18 inches; although the gap was held by just a single bolt between the ways it was also, for accuracy of location, dovetailed and doweled into place as well.
The tailstock was modified so that the pressure applied by the three clamping bolts was more evenly distributed - two still emerged on top of the tailstock, the third was repositioned in the centre of the well of the casting. Unfortunately, the same design of through barrel (which was ungraduated) was retained but, as an option, a worm and wheel driven barrel was offered - again based on what looked very much like a LeBlond-like design.
A more powerful main-drive motor was fitted - with 15 instead of 12.5 hp and two speeds instead of one - and the adjustment changed from a pivoting plate to vertical motor rails held within the headstock-end cabinet leg. The drive was by 6 V belts, as before, but the clutch was changed to one by Anderton which included a powerful brake; as before, the headstock clutch lever had its control duplicated by one on the saddle. With the two-speed motor the number of spindle speeds was doubled to 16 and spanned 12 to 400 rpm. The 4.125" bore headstock spindle was identical to that used on earlier models, but now ran in two Gamet high-precision taper roller bearings instead of the Timken variety previously used.
The screwcutting gearbox could generate 60 threads instead of the previous 50, but it was still necessary to change the (quiet-running fibre) feed gears in order to convert it to metric screwcutting.
Binns & Berry estimated that the lathe's work potential was the removal of 15 cubic inches of .45 carbon steel per minute.
|
|
