A depth gauge or Z-axis meter for the Unimat-SL (DB-200)
The Unimat DB-200 is a nice
mini lathe/mill/vertical drill machine. It has many of the features of
larger lathes, combined into a small package that fits nicely inside a
small room. One of the disadvantages that can be easily realized when
using the mill/vertical drill for the first time, is the absence of a
depth gauge (or Z-axis meter). To drill a hole at a predefined depth,
one has to drill it slowly in steps, removing the drill each time and
measuring the depth with an appropriate tool.
overcome this problem, I have decided to build such a gauge. The
requirement was that no modifications to the lathe should be done. I
realized that the lever that sets the Z-axis movement, allows a ring to
be installed around it, which with appropriate scale marked on it, can
be used for the purpose.
the ring is attached to the lever using a set screw, it moves
circularly along with the lever as you move it. The set screw, allows
for zeroing the scale as desired. All that is needed to complete the
gauge, is a needle and this can be made simply by drawing a line, using
a permanent marker, without modifying and ruining the lathe. A
permanent marker can be easily erased at any time using alcohol or
acetone, but it can not be erased by lubricants, that are most likely
to be used on the lathe.
have not included an automatic stopper for the depth because I could
not figure out how this could be done. However, neither the X or the Y
axis have such a stopper. The
scale has been calibrated by very carefully measuring the amount of the
Z-axis movement and marking the appropriate line on the gauge surface,
using a permanent marker. Then the scale lines were engraved onto the
marker lines. To keep the scale easy to read, each line represents one milimeter of the Z-axis
movement in my prototype.
the step of one milimeter per line does not seem too good at first, it
is in fact adequate for most operations. Nevertheless, one could never
expect to achieve the step size of the X and Y axis, because there is
not a fine pitch screw on the Z-axis. However, the milimeter lines are
close enough and the half milimeter can be very comfortably set by
observing the two adjacent lines and halfing their distance. Going to
less than half milimeter is not very practical, considering the
backlash of the lever. In such a case, you can always use an external
precision depth measure gauge.
To finish the gauge, a knurling tool was used to make a diamond pattern
on the aluminum ring and the stainless steel set screw, so that they
can be both set quickly using your fingers, with no need for a tool.
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