Faced with the need to engrave a dial, typically for a lathe lead screw, then it
is probable that three line lengths will be required. The longest for the tens, mid
size for the fives and shortest for the units. Often the method will be to use the
top slide with suitable cutting tool and control the lengths using the slides calibration.
This can be a little tedious. Additionally, one must count the number of lines being
made to decide when a tens length or a fives length line has to be made.
The lining tool, the subject of this project, largely overcomes the problem as it
automatically sets the line lengths, also knowing which length of line to engrave
at each location. Internally, it includes a 10 tooth ratchet that advances the cam's
rotation by a tenth as each line is completed, the cam having been cut to set the
line length at each position, Photograph 1 should make this clear.
If however, a dial is being engraved for a metric lead screw where 0.1mm will require
the longest line and increments of 0.025mm the shortest lines. This would require
the cam to index just four times in one revolution which would be difficult to achieve
with the method being used. Therefore, the cam is made to suit, one long, three short,
one long and three short for one revolution of it. This though is just 8 divisions
and above a 10 tooth ratchet was mentioned as being fitted.
Photograph 2 shows the parts that make up the device from which it can be seen that
there are two ratchets, one of which is 8 tooth. To fit this, the tool will need
partially dismantling to change the ratchet, it is though a quick and simple task.
The photograph also shows that there is just one cam and that both the insets are
the same depth, this being for the metric example above. A cam having insets of
differing depths would be required for the tens, fives, units dial, as required for
an imperial lead screw. Photograph 3 shows the tool being used.