Referred to here, this is not the brightly coated or anodized aluminum we use to make plaques or trophy plates. This is machining grade aluminum found in the construction of control panels, interior and exterior signage, and for industrial applications. Aluminum can be temperamental and can be compared to brass, copper and bronze in cutting difficulty. Almost all aluminum will cut with some experimentation and patience. There are too many grades or alloy numbers of aluminum to mention, but a few deserve special mention:
A slow Z-axis plunge speed is recommended when entering aluminum material. None of the cutters in the aforementioned paragraphs are designed for aggressive plunges such as drill bits. It is also recommended not to go too slow when cutting aluminum. Slow feed rates mean higher friction. Try speeding up the feed and lowering the spindle rpm. When cutting any metal, always use a coolant misting system to reduce heat buildup and increase tool life. At a minimum, add coolant to the aluminum surface before or during the cutting process to lubricate and cool the cutter.
Commercially purchased brass will probably be very hard for engraving. "Engravers Brass" or "half-hard" brass is much softer and can easily be deep cut. Half-hard brass may also be referred to as "red brass" or "leaded brass". Engraving material suppliers usually have a stock of this softer brass. If you must source this material from a local house, be sure to tell them that you plan on engraving the material. For deep cut signage, brass with a thickness of .040-.060" is recommended. This material can be paint filled for contrast between the letters and the brass background.
Trophy brass and aluminum is generally sold in 12"x 24" size sheets. The material is usually .020" or .050" for brass, .025 for aluminum and .015" for brass plated steel. Brass plated steel yields the look of brass but at a reduced cost, about 1/2 of the price. The brass or brass plated steel can be diamond dragged or burnished using carbide or rotating diamond tools. The anodized aluminum can be diamond dragged. Burnishing aluminum does not give very satisfactory results. The tools tend to gouge the material and the finish becomes rough. I only recommend using aluminum if a specific color of the finished plate is required or if the job must be produced with the least expensive materials. Aluminum has found its way onto millions of inexpensive sports trophies and should probably only be used for this purpose. High-end awards warrant the look of a solid brass plate.
Although each of these materials is unique, some general rules can be applied. These metals are soft by their nature and are easily cut. In most engraving applications these will be found in gift items, so diamond drag engraving will be the method of choice. These materials can be deep cut easily and the same tools that are used for brass and aluminum may be used. In most cases no cutting fluids will be necessary.