A dial bore gage must be “set” to a reference master that has a known dimension. The master may be a cylindrical master ring or two flat surfaces that are accurately spaced to a given dimension. Mastering a dial bore gage to a master ring gage is the preferred method because the ring gage duplicates the geometry of the workpiece being gaged. It is accepted as the quickest and most economical for high production gaging. It is also the most precise, especially for bore sizes under 1 inch, or any bore sizes that require master quality finer than “X” accuracies. Master rings have the further advantage of being more directly traceable to the National Bureau of Standards than any adjustable or multiple component device. Mastering to flat parallel surfaces is a practice generally related with dial bore gaging of larger allowances – or short-run job-shop applications that do not justify the cost of a extra master ring gage. Mastering to flat parallel surfaces requires substantial operator skills in generating an accurate gaging contact axis in two right-angle planes at one time.
Any dial bore gage “set” between parallel flat surfaces (as with gage blocks or bore gage setting master) must have gaging contacts free from wear. Any “flats” on the gaging contacts will cause an error in “setting” that is approximately equivalent to twice the height of the chordal segment that is made by the radius of the bore and the width of the flat on the gaging point. The use of maximum wear-resistant material substantially reduces the possibility of worn contact errors. Norbide, tungsten carbide or diamond-tipped gage points are representatives of the materials that should be used.
Most optical comparators are rugged machines that can work in virtually every environment. However, proper care and precautions can guarantee longer lifespan of such device.
The first element that needs proper care is power supply. Optical comparator should be plugged into power outlet rated at minimum of 15A. It should be connected only to outlet with proper ground. Optical comparator power supply features cooling fan. In order to proper operation of the unit sufficient cooling must be supplied to power supply. If the fan fails, the power supply is in danger of overheating. If the fan is working intermittently it is most likely due to a power interruption either inside the fan or in the wires that supply the power to the fan. Check the connectors for the fan power wires to make sure they are tight. Check the connections at the transformer to make sure they are also tight. Look over the fan wires and make sure they are not frayed or pinched between any parts of the machine. Check to make sure there are no obstructions in the fan blades such as wires or a piece of paper. If everything looks ok, the power interruption is most likely inside the fan or is mechanical, due to wear or contamination causing binding. In this case the fan will need to be replaced.
Optical comparator has some moving parts inside. Moving parts are most likely to fail because of wear and tear. One example is focus bearings. However it is very unlikely that those bearings fail, proper care should be considered. Removing instruction is beyond the scope of this article so we are just going to focus on cleaning. Bearing surfaces should be inspected with a 3X loop, then clean or replace the focus bearing rails or bearing cages as necessary. If the rail surfaces look slightly dented then they should be carefully checked that they are truly dents and not just a buildup of varnish or old oil. These “dents” should clean with solvent. Also bearing rollers should be inspected for possible buildup of varnished oil.
