Home Shop Machinist

Trail of crumbs.


The Smithsonian Channel’s Alaska Aircrash Investigations is a documentary series that follows Anchorage-based NTSB investigators as they respond to and analyze airplane accidents. What makes the show different from Smithsonian’s other show, Air Disasters, is the focus on small plane mishaps.

The manufacturer of this aftermarket VW cylinder head stamped ID marks in two places. I have no idea what they mean. If someday it becomes important, I am sure somebody will!

When it comes to aviation safety, crash investigation shows provide food for thought. Watch and learn. Aircrash investigators consider every scrap of information, no matter how small, as important. In one segment, factory markings on a propeller suggested it may not have been approved for use on that plane. This led the team to consider if it could have been a factor, if not the ultimate cause, of the crash. While the particular aircraft and propeller in question were not Experimental, it got me thinking: When, where, and what type of maker’s marks might an Experimental builder use?

Manufacturers of airplanes—big brand or small and individual builders—have an obligation to leave more than a trail of crumbs to document their work. Logbook entries may be the minimum requirement, but that doesn’t mean you can’t put strategically placed ID marks on important or custom components. When someone sees a “born on” date and your initials on the part, it provides an immediate clue to its origins. Such maker’s marks can be a big help to future maintainers or, God forbid, crash investigators, should the need ever arise.

Comparison of letter stamping, vibrating pen and a chemical-etching on stainless steel.

Identification codes can be as simple as your initials and the date, or a drawing number, if there is one. On my Bob Fritz-built Jabiru, some of the fiberglass parts were marked with a Sharpie. Jim Weir provided some great tips for marking electrical wires using printed sleeves (see Aero ‘lectrics, January 2017). Sharpies and labels have their place, but since this column is about machine shop methods, we’ll look at engraving, which can be mechanical or chemical, and stamping, which can be achieved by embossing with a metal stamp or with a rubber stamp and indelible ink. There’s no universal right or wrong choice for all cases. Each has advantages and disadvantages.

A vibrating engraving pen can quickly and permanently ID this propeller crush plate.

The old standby for quick-and-dirty engraving is the vibrating metal-marking pen. They are easy to use and qualify as permanent because their markings can’t be erased or destroyed, at least not easily. One issue with them is, if your handwriting is lousy, you run the risk of making a mark no one can read. Because engraving gouges and scratches the metal, there is the potential to compromise the integrity of a component. You should never, for example, engrave on thin-wall tubing or on areas of parts that may be subject to flex. In those cases, either skip it or mark it with an ink stamp, Sharpie or adhesive label. The last thing you want is to unintentionally create a stress riser. This goes for any method of embossing or engraving.

The Etch-O-Matic “super” kit.

The blue carbon paper is the stencil used to etch the mark on this homemade chain-breaker tool. The white card is a backing sheet to prevent the stencil from tearing when you type or write your pattern.

Until low-cost industrial lasers came around, electro-chemical etching was the universal method for marking mass-produced knives, high-speed steel cutters and drill bits. It’s still very popular for low-volume work and one-off parts because there’s literally no set-up cost involved. The system will work on any conductive metal, including stainless steel, brass, copper, bronze, titanium, aluminum, tin, and zinc. It can also be used over black oxide coatings. The area to be marked should be clean, but does not have to be sterile or polished, although the more visible tool marks are, the more they tend to reduce the crispness of the image.

The Etch-O-Matic “super” kit (shown below) costs around $250 and consists of a transformer, a marking head with a felt pad, a supply of stencils, and a bottle each of electrolyte and neutralizer solutions. A basic “starter” kit, which includes lesser quantities of the stencils and solutions and has a smaller power supply integrated into the transformer/marking head unit, sells for a very reasonable $90.

To create a mark, you put a sheet of paper over the provided stencil material and write or type the information you want to etch. The stencil material appears to be nothing more than carbon paper (if you don’t know what that is, ask someone who was around before computers and smartphones). I keep an old IBM typewriter around just for making Etch-O-Matic stencils.

Once you have the stencil, you are ready to make a mark. Attach the ground clip to the part to be marked, plug in the transformer, moisten the marking pad, position the stencil and, being careful not to allow the stencil to slip or move, gently press the moistened pad onto the stencil and count to three. That’s it.

Embossed metal letter stamps are pretty straightforward. I have several sets, but I rarely use them for anything other than making single-letter designations (such as revision “B,” etc.). To be frank, when it comes to spelling out a word or making a number sequence and getting the characters lined up and perpendicular, I suck. No matter how I try, it looks like the work of a 5-year-old. I could buy or build a stamping fixture to space and hold the stamps correctly, but if the job is that important, it’s quicker and faster to use the Etch-O-Matic system.

The set of metal stamps on the left are 3/16-inch tall letters and the set on the right are -inch tall.

Rubber stamps may seem pretty low-tech, but with a good indelible ink such as StazOn, you can make professional looking marks on any rigid material without any of the structural risks associated with embossing or engraving. Rubber stamps are cheap and come in all shapes and sizes. I paid less than $15 for the 13-character, alpha-numeric stamp shown. Provided the surface is clean and dry, marks made with StazOn ink will not fade or wash off with soap and water. While the ink is not resistant to solvents like alcohol and acetone, there are plenty of parts that get installed in places that will never be subject to solvents or chemicals.

This 13-character alpha-numeric stamp with StazOn ink can make professional-looking marks on almost any rigid material.

For more information on parts marking, see FAA Advisory Circular 43-213A, Parts Marking Identification.


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