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.

To 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.

If 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.

I 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.

Although 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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