Civil Engineering Reference
In-Depth Information
Fig. 7.6. A depth micrometer comes with interchangeable rods so it can be used for
various depths.
WHAT IS BACKLASH?
Backlash is the wear in the machine's feed screws. When you wind the handwheel to
zero in one direction, the table is in one set position. When you wind the table to the
same zero from the other direction, it will not be in the same position as when you
wound it in the first direction. The difference in these two positions is the backlash.
This will only be a few thou at most, but it is still a nuisance. So, when accuracy is
important, always wind the handwheels in the same direction even if you have to wind
it back a few turns and then wind it back to zero again.
Machining shims
Occasionally you may be called on to make some very thin shims. They may
only be 10 thou or so thick. The easy way I have found to make these, assum-
ing the shim has at least one hole in it, is to carefully cut the shims oversize
with a pair of tin snips. Then clamp a piece of aluminium sticking out from the
vice. Put the shims on top of the aluminium, put another piece of thicker alu-
minium on top and clamp the lot together with a couple of toolmaker's clamps.
Carefully drill the required holes in the shims and fit nuts and bolts through
the entire package and tighten them up. Remove the toolmaker's clamps and
you can now machine round the outside profile of the shims. Undo the bolts
and remove the finished shims.
