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After getting facinated by machinetools and subtractive manufaturing, I developed an interest in precision mechanics, and how that precision is achieved. So, like any normal person I spend a significant chunk of my money on equipment and materials to learn about it, and do it myself.
Disclaimer: This is kind of missplaced in the projects category. This is going to be simply a collection of stuff, techniques, fun facts, some actual projects and anything I can think off that fits the topic. And if it gets too big I'll split it off into a seperate list of links.
An essential tool in making precise surfaces is removing small amounts of material in specific spots. One of the older ways to do this is by scraping it. Originally with a tool made from hardened Steel, nowadays more commonly with a carbide blade. This tool would be sharpened with an optuse angle of usually about 95°, or a negative rake of 5°. That way the tool only removes about 10 microns (~0.0004") at a time (this amount will of course vary, based on various factors like the pressure being applied, the sharpness of the blade, and several other factos). This depth somewhat limits the accuracy achievable with scraping. Generaly scraped surfaces can be made to about 5 microns (~0.0002"), though we usually only consider the local high points as part of the surface. The valleys that the topology of a scraped surfaces inherently include don't affect most applications (negatively) and are therefor usually mostly ignored. Common applications include measuring equipment (such as surface plates), machine ways (hydrodynamic bearings benefit from a scraped bearing surface, because oil gets trapped in the valleys) and matched flanges
Another way to remove small amounts of material is by lapping. By rubbing two parts against one another with some abrasive grit inbetween the two the area of contact will be worn down, removing high spots. Common abrasives are Alumininum Oxide (aka corundum, ruby, saphire, and probably a thousand more names), silicon carbide, zirconia and diamond. What abrasives should be used depends on how much material needs to be removed and what material is being worked. Further a differentiation is made between lapping with free abrasive, that is tumbled between the surfaces, and lapping with a charged lap, where the abrasive is embeded in the soft lap. Lapping is used for even higher precision, and when the surface can't have the topology of scraping, reaching well into the nanometer range. Common applications include even better measuring equipment (sometimes, when the topology isn't a problem surfaces are scraped and then lapped), optics and sharpening scraper blades :D
Another way to remove small amounts of material is by lapping. By rubbing two parts against one another with some abrasive grit inbetween the two the area of contact will be worn down, removing high spots. Common abrasives are Alumininum Oxide (aka corundum, ruby, saphire, and probably a thousand more names), silicon carbide, zirconia and diamond. What abrasives should be used depends on how much material needs to be removed and what material is being worked. Further a differentiation is made between lapping with free abrasive, that is tumbled between the surfaces, and lapping with a charged lap, where the abrasive is embeded in the soft lap. Lapping is used for even higher precision, and when the surface can't have the topology of scraping, reaching well into the nanometer range. Common applications include even better measuring equipment (sometimes, when the topology isn't a problem surfaces are scraped and then lapped), optics and sharpening scraper blades :D
To be able to use these methods to create accurate surfaces it's neccessary to know where to remove material. The arguably easiest way to do this is to "Print" of a master the surface of wich will be copied. To do this, a thin layer of color (typically Prussian/Engineers/High-Spot Blue, which is a non-drying blue paint) is applied to the master. Then the Workpiece is rubbed against this master, and anywhere where the pigment is transfered material is removed. This Methid has it's limits, because the surface being scraped can't be too smooth, because if it is, the paint will smear. This makes it particularly practical for scraping.