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Taig
lathe carriage leadscrew / split-nut:
(click on the thumbnails for a larger image)
Adding
a leadscrew/split-nut to the carriage axis was a very successful
modification. It sets the carriage axis up to be driven by
a stepper motor and also allows for very even, fine feeding
capability when using the lathe manually. The leadscrew is
1/4-20 stainless lefthand threaded rod. I chose lefthand
thread because it makes using the crank at the right end
of the lathe
a more normal action. You turn the crank away from yourself
to feed the carriage into the spindle. A split-nut is used
to engage and disengage the leadscrew. This nut has two halves
which are clamped against the leadscrew to engage and unclamped
to disengage. When the split nut is engaged, the crank at
the right end of the lathe (manual mode), or the stepper
at the left end (CNC mode) can move the carriage by rotating
the leadscrew. When the split-nut is disengaged the stock
crank on the carriage can be used to rapidly move the carriage
using the stock Taig rack and pinion arrangement.
The
leadscrew has to be mounted very precisely in terms of being
parallel with the bed of the lathe and it must be square
to the side of the carriage. The side and end of the carriage
(which is a casting) were milled flat and square then a hole
drilled through in order to pass the leadscrew through it.
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The
top picture shows the carriage, leadscrew and split-nut
assembled.
The
middle picture
shows the finished split-nut mounted to the side of
the carriage. The brass knob in the
front
is
rotated by the operator about two turns in either
direction in order to turn a screw which drives the
two halves
of the nut together or apart. The screw has opposite
handed threads on either end and the two halves of
the nut are drilled and tapped to match.
The
bottom picture shows the rails on which the two halves
of the nut track in order to remain parallel in
closure. The acrylic shield helps to keep swarf
out of the nut cavity.
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The
top picture is the operator's view.
The
middle picture shows a small acrylic window on top
of the assembly which allows the
operator to view the halves of the nut closing
onto the leadscrew.
The
bottom picture shows all the parts laid out. A thin
steel plate is used to mount the parts and secure
them to the carriage. A small spring is used to assist
the separation of the nut from the leadscrew during
"disengagement".
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This
drawing is not dimensioned but it may help visualize
how things work.
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Last
changed
February 26, 2003
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