|
Probably the best choice as both wood and metal can be turned. It is also easier
to adapt and make the specialist chucks and accessories used by an ornamental
lathe.
Machines by either Messrs. Myfords or Boxfords would probably be the best to
obtain, both being capable of being driven at high or low speed and having wood
turning attachments and other accessories available. This is not to say that
other makes are not suitable as there are many other makes available especially
secondhand but, care should be exercised if choosing a "Foreign
clone". The older Colchester and Harrison Lathes are generally too slow
although their more recent models have a greater and more useful speed range.
If buying second hand a simple check can be carried out described below under
"Tailstock". At left hand end of the bed is the headstock where the
drive is situated and a good range of speeds must be available ranging from
around 40rpm to at least 1500rpm. It should have a hollow mandrel and at least a
number two Morse taper socket in the nose for holding centres and other tooling.
The chucks will either fit by means of a screwed external section on the mandrel
or on some top quality machines onto a taper and held in place by either a
locking ring or cams. These latter two fixings are ideal as they securely hold
the chuck under both forward and reverse motion whereas a screwed fitting will
undo under reverse. (It is possible to make up a simple locking ring to prevent
this providing there is sufficient room behind the chuck fixing thread).
At the other end of the bed is the Tailstock which can be clamped at any point
along the bed and serves to support the work in hand whilst turning. Like the
mandrel it should have a hollow barrel with ideally a number 2 Morse taper
socket for holding centres of various types as well as drill chucks and other
cutting devices. A simple alignment check can be carried out by placing centres
that have been checked previously into both the Headstock Mandrel and Tailstock
Barrel and seeing how well they line up then swap them around and check they
still line up. The tailstock has (usually) alignment screws for offsetting the
centre for machining tapers but there will be no adjustment for vertical
discrepancies although where the fault lies in wear of the tailstock it may be
possible to use shims. The barrel should preferably have a graduated scale for
depth / travel measurement. The carriage runs on the bedways and is controlled
by a hand wheel which engages a rack attached to the bed and carries a further
part the top slide which in turn has a fixing for the cutting tool. The top
slide should be attached via a circular spigot so that it can be rotated and
locked in position to allow cutting to be done at any angle. It's removal
generally leaves a socket into which other accessories can be fitted such as
hand turning rests for both wood and metal or a vertical slide. A further
control on the carriage (normally a lever or pin) engages the "lead
screw" a threaded rod that runs the length of the bed and connected to the
headstock mandrel by a set of gears. This allows for cutting threads or for
semi-automatic feed.
NOTE : This
facility must not be used for converting wood from the square to the round as
the shock loading will in time cause the teeth of the change gears/gear wheels
to fracture and break off.
|