The cutting of extremely detailed parts from brass, copper, and steel sheet metals, with no rough or bent edges, is generally considered to be a job for massive machinery which can cleanly punch out products by the thousands. This process below is simple, and does a fine job on all the metals mentioned, with the exception of Stainless steels. This method works so well it can be used to make metal parts for art, models, and even some machine and electronic parts. Fine engraving is also possible. Read on.
The advantage to this recipe and system of work is that it utilizes easily available but somewhat specialized materials, and the original author and inventor was well acquainted with chemicals and their reactions. For instance, one of the accepted ways to accomplish this has always been with nitric based acid baths -- and this is only partially true: Nitric acid baths generally create a FOAMING in most reactions with metals , and this disrupts the integrity of the wax shield at the edges, causing roughness, and unevenness.
The acid for this method is made like so:
3 Ounces potassium bichromate dissolved in 32 ounces of water, then 3 ounces of concentrated sulphuric acid is added. That mix there is also known as Photographers CHROMIC-ACID TRAY CLEANER. If you can get that premixed that saves time. Next an emulsifying oil is added to this mix, and that is a key to making this all work, as it gives the solution greater wetting power, and allows it to soak into the finest of lines scribed through the wax coating. A few drops ONLY of any emulsifying oil will make this a very efficient acid bath for the purpose of cutting out finely detailed parts. Rust inhibitor for car radiators works well, and liquid detergents will work too.
If aluminum is to be cut, add half ounce or so of hydrochloric acid to the above mentioned acid bath. When any metal but copper is cut, stir the bath frequently during the operation, to defeat any encrustations which may result, and slow down the etching. Preserve this mix after use by straining and storing for future use. Dispose of, when spent, by evaporation in an outdoor shed.
The metal to be used can be very thin sheet metals, and up to 1/16th inch thick or even thicker. The time required to cut the part is dependent on temperature (80 F optimum), and the thickness and type of metal. Experiment on scrap or practice pieces before tackling bigger jobs. Fine acid engraving can be accomplished with this process too, by allowing the metal to soak for only half the time, or less, which was required to cut the metal. That is very handy information indeed. Anything can be traced onto the wax, then scribed down to the metal so that the acid is allowed access: even photographic images can be engraved or cut out!
The wax coating is also very important to this process, and has to be of syncera or ceresin wax. Regular crayons usually work fine. Heat the metal slightly and dip in molten wax so good UNIFORM and TOTAL coating results. Let drain and dry by hanging until wax gets hard and everything is room temp. This coating will be what you draw your design through. It can be etched with a scribe or any sharp tool. You can trace a design easily on the wax, then go back after, with an exacto knife or something like it, and cut through the wax to expose the metal surface which will be cut by the acid. A template or tracing design can be held to the waxed metal with a dab or two of contact cement. Remember: where ever metal is exposed, the acid will cut.
Finally, it is very important that your metal be 100% finished before coating with wax, and cutting in the acid bath, because trying to polish a finely cut piece of sheet metal is ludicrous. Also, this polishing beforehand must entail total cleaning of the metal, because grease of any type will resist the acid bath and cause problems. Benzene works well as a final cleaner right before the wax coating. Remember your skin has oils too, so handle at that stage with rubber gloves if possible. You cannot be too careful. After the etching process, clean it all up with gasoline. If the type of wax you used does not come off with gas, use low heat in an oven until all the wax drains off.
For safety wear a good rubber apron, goggles or safety glasses, and gloves at all times, when handling chemicals such as explained above. Perform this job outside and don't breathe the fumes at all.
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