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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:
- Hard 60 - 61 - T-6 or 6061 is a good hard alloy aluminum that is general purpose. You can find this in both sheet and bar form from most metal supply houses. This material takes to other processes like anodizing, painting, sand blasting and brush finishing. When cutting .090 or thinner material, especially clamped on the edge, a single or two fluted straight flute cutter will keep the material from lifting off the table by reducing vibration. It's recommended that you use a solid carbide tool for prolonged cutter life. When cutting .125 and thicker, a single flute up-cut spiral is recommended. This cutter will remove larger chips and reduce heat buildup. As a rule of thumb, it is best to never exceed the width of the bit with the depth of the cut. For example: cutting a piece of aluminum .5" thick with a 1/8" tool, it is recommended to cut in at least four passes.
- Soft 30 - 31 - Never use a two-flute spiral cutter when cutting soft aluminum. The aluminum will gum up in the cut, and be welded back together. To achieve proper chip size, it is recommended to use a .187 or larger bit.
General tips on cutting aluminum:
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
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.
GOLD, SILVER, PEWTER
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.