Harold Hall

Workshop Projects


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 holes.


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.

Using a Centre Finder, on the lathe.