At this stage the assembly is unlikely to be balanced, considerably off balance if
a complex shape component is being machined. If then the lathe is started up it will
shake excessively making machining quit impossible and if the part needs to run at
a high speed due to the machining taking place at a small diameter then it may even
To balance the assembly weights must be added where the tests indicate. For these
weights I use T nuts as used on the milling machine and where these do not provide
sufficient weight then 10mm thick steel plates about 50mm square of which I have
a number from another application. The reader will no doubt have some items around
the workshop that will suffice.
Set the lathe spindle to run as freely as is possible, by freeing the drive belts
if belt driven or setting the gear box to neutral if you have a geared head. With
that done spin the faceplate and take note where it comes to rest doing this three
or four times to be sure it is a genuine position. Take note of the lowest point
realising that this is the heaviest side and add a weight to the faceplate on the
opposite side and carry out the test again.
If the faceplate still stops in the same place more weight will be required or if
it is possible move the added weight further out on the faceplate. If it though stopped
on the other side then less weight should have been added or the added weight moved
nearer the faceplate's centre. Tests should continue to be made and weights added
until the faceplate stops randomly when spun at least six times.
Unfortunately, though, the drag in the machine's bearings will inevitably prevent
one from getting anywhere near a perfect balance resulting in the lathe having to
run at a speed much lower than is ideal. My answer to this was to produce the balancing
fixture seen in Photograph 16, with which a much superior balance can be achieved
and the lathe can then be run at the appropriate speed for the machining taking place.
The fixture is well worth making if the viewer is going to use the faceplate from
time to time as it does enable a much superior balance to be achieved. Its main feature
is that it has my own form of ball races using cheap balls obtained from the local
cycle repair shop. As a measure of the success of the design it runs for around 25
seconds if an empty faceplate is spun rapidly. This compares to just two seconds
for my series seven lathe.