| Rex Swensen's Web Site Optical Centre Finder for Zeroing Coordinates |
When working with CNC it is imperative that the zero point in X and Y be
accurately established. In clock plates, for instance, if a series of pivot
holes are to be accurately drilled relative to a certain point, then this point
must be very accurately established. To facilitate this, an optical centering
microscope is highly desirable, so that the axis of the spindle may be aligned to say a certain reference.
Such devices are quite expensive, so I built my own, based on a design published in Model Engineers Workshop, Issue No. 1. I modified the design to incorporate a magnifying lens salvaged from an old 8mm movie projector. It gives about a 2:1 magnification.
The heart of the device is a special home made perspex square section optical "lens-prism", which has a polished surface at 22.5˚ to the machine axis. This acts as a mirror due to the internal reflective properties of perspex. Additionally the two ends are polished. The body is machined from aluminium, with a rectangular slot for the lens-prism. The viewing leg is at 45˚ to the machine axis.
A tiny conical indentation has been made exactly on the centre axis in the lower polished end, and this white dot is aligned with the target as shown in the second photo. This photo has been graphically enhanced to make it clearer. The device may be used in a conventional drilling machine or lathe.