O Features archive - February 08
O How to...
Choose a lathe
I defy any one of us to deny we’d love a lathe in the workshop but what to choose? We asked Tony Griffiths from www.lathes.co.uk to give us an idea of what to look for.
What makes the perfect workshop? I think we can all agree on a warm, dry space with a well-lit bench of stout construction, a strong vice, a good selection of quality hand tools and a bench drill.
However, what you really need is a lathe. The lathe can turn, bore, grind, drill and generate screw threads. With a few simple modifications and/or practice, the user can produce flat surfaces, make the most precise of components, machine a crankcase or rebore a cylinder.
Finding a lathe can be just as exciting as locating a long-sought-after motorcycle; you just never know what’s going to turn up. The main considerations are: will it do the job – to buy new or used – and how much to pay?
The market is now awash with cheaply built machines from China – that country having largely displaced the former leaders, Korea and Taiwan in the manufacture of these products. Machine tools from all these countries offer a lot of ‘metal for the money’ however they sometimes lack several vital elements such as: quality of materials; care in assembly and set up; tumble reverse; backgear and a selection of slow spindle speeds.
British and American small lathes normally include most of these essential features. However – and this cannot be overstated – these features make an enormous difference to the usability and functionality of any lathe.
The result is that a second-hand but properly specified British, American or European machine can be worth as much as and sometimes more, than a new Far-Eastern example. ‘Regrets about the low-quality last far, far longer than the celebrations over the low price’ applies well to machine tools. However, not all is doom and gloom, some imports really are quite decent. Inspect the intended purchase personally and it’s possible to pick up a bargain.
Size
The ‘English’ method of sizing a lathe is to quote the centre height – or ‘throw’ – the distance from the centre of the chuck to the nearest point on the bed. The American method quotes the largest diameter of a workpiece that can be turned clear over the bed – termed the ‘swing’ – instead. So a 4 x 24in using UK terminology would equal an 8 x 24in USA size.
How big to go? Well, bigger is not necessarily better – and moving larger machines can be an expensive proposition. For motorcycle work something between a 3 x 15in machine and 6 x 30in (UK sizes) would be suitable – the former would be light enough to lift off the bench yourself, the latter needing an engine crane and a trailer to get home.
Lathe beds
Arguments have raged long and hard over the best profile for a lathe bed and the claimed merits of English flat and American V-ways. On smaller lathes there can be no doubt that it simply does not matter which one you have. Claims favouring one over the other are just that, claims. In practice you will be able to discern absolutely no difference in performance between them. Round-bed lathes with single or twin bars, have always been available, some designed down to a price but others of almost toolroom quality.
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