Acid-Etching part 4

THE ACID-ETCHING MACHINE AT WORK

Setting up the machine is the most critical step in its operation:

First, a long vent hose is made up to the PVC vent pipe atop the lid. This hose is run out the shop door and well clear of the house. From my air manifold I run a hose to the machines air agitation manifold and adjust the regulator to deliver less than one PSI of pressure. A hand valve between the regulator and machine is then positioned 'shut'. Approximately one gallon of Ferric Chloride acid is poured in to fill the machines vat to a level even with the lower edge of the lid mounting foundation.

Then I energize the installed heater and wait (about thirty minutes) for the acid to assume operating temperature. The lid is maintained in place and secured with a weight atop it to seat it down tight on its rubber gasket - this to assure that acid vapors don't find their way into the shop.

A large container of fresh water, big enough to permit complete dunking of the acid-etching machines lid, is set by the machine. The waters principle use is to wash off the work as I check progress of the cut. However, this tub of water also serves as an emergency wash-down in the event of accident. The moment of a spill is not the time to be flopping around looking for a quick wash-down source!

The work being taped to the foundation piece attached to the upper lid of my acid etching machine. When the lid is placed down on the machines vat, the brass becomes entirely immersed in the hot acid, and the cutting starts in earnest.

The developed brass plate(s) are readied by sticking masking tape to an edge. The shop is readied by cracking the door, putting the ventilation fans on high, lifting the lid off the machine, dunking it in water to kill any acid that got on the lid mounting foundation, dried with a rag, and the brass plates secured with the attached masking tap. The lid is then plunked down onto the machine, the securing weight placed atop the lid and air is admitted in brief spurts using the air-valve. After about one minute of acid immersion, the work is pulled, dunked in the water, and examined to see if any cut-through has been achieved.
 

My acid-etching machine at work. Note the frothing bubbles at the surface of the hot acid which works to scrub off the oxides formed on the surface of the metal being cut. The white PCV pipe 'chimney' caries away acid vapor laden air away from the shop, my tools, and my lungs! Poor neighbors.

The thing to watch for is an even cut across all areas of the sheet - we want to see daylight through the sheet at all spots where metal should be removed, occurring at the same time.

One minute of work reveals most of the plate completely cut through. I achieve cut-through on five-thousandths thick brass plate using this machine in about three minutes. Hot acid and vigorous agitation of the acid are the keys to quick cuts with the minimum of undercut. Most common plastics are impervious to Ferric Chloride attack and are used to make the machine you see here.

Two to three minutes are enough for the acid attack on both faces of a piece of five-thousandths thick brass to achieve cut-through using this machine. At that point the fret of brass is pulled off the lid foundation and tossed into the fresh water bath, completing the acid-etching operation.

The completed work.

A detailed discussion on the end-use of acid-etched items is a topic for another time. You have more than enough to absorb here!

...And why am I putting so much effort into presenting this stuff to rank amateurs, anyway? Hell... most of you can't even fill a seam properly! Why do you need to know these advanced techniques? Who cares, anyway?   Maybe I should concentrate on the ABC's of kit-assembly, something the Guild members might be able to grasp.

David Merriman