Slider Blocks C14 and C15 These are without doubt the most critical parts of the
whole assembly, except that is for the spindle itself. Being made from cast iron
it is unlikely to be accurately to size as purchased and will need to be machined
to size, and without milling facilities this is done in the four jaw chuck, Photograph
8. Having done that it will be a question of marking out and accurately positioning
The crucial requirement is the relative position of the hole for the column in relation
to the holes used for fixing the blocks to the spindle mount and even more so the
face in which these are drilled. As the holes are on different faces it is not straight
forward. The actual dimension is though not critical but that they are all identical
is. The following should make this relatively easy to achieve. Mark out the positions
for holes A and C and drill and tap as per drawing. Also mark out the position for
hole B on one block only.
Provisionally mount a length of angle, or square mild steel, on the drilling machine
table and with two cap screws in holes A, position the heads of these against the
end of the angle. Using a toolmakers clamp, or similar, clamp the two together. Now
adjust the position of the assembly such that a centre drill in the drill chuck lines
up with the marked position for the hole for the column. Clamp in place on the machine
table and centre drill, Photograph 9. Remove the block and fit one of the unmarked
blocks, again fitted with two cap screws, and centre drill. Repeat for block's three
and four. With care, this procedure will ensure that they are all the same.
Now, with the four jaw chuck mounted on the lathe and using a centre finder, set
the centre to run true, Photograph 10. Do pay particular attention to this task as,
whilst the clearance holes for the screws will permit a small error, the distance
to the mounting surface is vital. Any variation in this dimension and the assembly
will not move freely on the bars, as I found on final assemble. At this stage I had
to include a shim under one of the blocks.
Bore the first block a close fit on the precision ground column, repeat for the other
blocks, Photograph 11. However, make two off C15 oversize by about 0.2 mm. Mark the
two bored oversize so you know which they are when assembling.