Complete Guide to CNC Engraving [Laser, Metal, Wood, Machines]

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CNC Engraving is one of the most interesting and artistic things you can do with a CNC Machine. In this guide, you're going to learn everything you need to know to tackle your own CNC engraving work.

What is CNC Engraving?

Engraving is the art of carving a design into a hard surface. Typically its done by hand, using an assortment of hand engraving tools:

Image via Wikipedia

This is a laborious and difficult to learn process. Fortunately, CNC machines are capable of very sophisticated engraving.

Sometimes CNC engraving is purely utilitarian, for example to add a serial number to a part. Other times it is an artistic embellishment. The type of CNC Engraving Machine you have will determine most of what's needed to engrave.

CNC Engraving Machines

CNC Engraving is typically done either by a laser or by a rotating tool in a milling machine or CNC Router.

Laser Engravers and Machines

Image courtesy of Epilog Laser...

Lasers can be used to engrave in two ways. First, if the laser engraver is powerful enough, it can cut the material. Second, even if it isn't powerful enough to cut the material, it can discolor it in a visually distinctive way using a process called Laser Marking.

In many ways, laser engravers can be simpler than machines that use rotating cutters. The reason is a simple XY position will suffice-no Z axis is necessary with the laser.

They also have the great advantage that the laser beam imports no force to the workpiece, so workholding is not an issue. Often the workpiece just rests on the laser machine's table without anything but gravity holding it there.

Materials that can be engraved

Many materials can be cnc engraved by laser including:

Wood: The laser carbonizes or burns many natural materials like wood and leather.
Leather
Plastic
Metals: Metal requires a lot more power and sometimes specific laser types that operate a frequencies that work more efficiently with metal.
Coated Materials: Sometimes it's easier to engrave with a laser that burns away or discolors a particular coating. There are specialty coatings made for exactly this purpose.

Common Laser Types

Laser Diodes

Very low end laser engravers use laser diodes and are typically less than 5 watts in power. In fact, 5w laser diodes are rare and most are much less. These lasers can't do much at such low power levels, so they're more a curiousity than anything.

CO2 Gas Lasers

The most common type of laser in laser engraving machines is the CO2 Laser. These layers use a tube filled with CO2 (carbon dioxide) gas. They have very high efficiency and beam quality, plus they're fairly cheap. That's why they're so common. They're best suited for processing non-metallic materials. CO2 laser engravers have gotten quite inexpensive and commonly available. You can pick up a 40W laser engraving machine from Amazon for a little over $400.

Fiber Lasers

Fiber lasers are solid state lasers that work by generating a "seed" laser beam and then amplifying it in specially designed glass fibers. They produce a beam that's 100x more concentrated than a CO2 laser, which makes them ideal for metal applications. They're also good for plastics.

Crystal Lasers

Crystal Lasers are pretty similar to Fiber Lasers from an application standpoint.

Laser Power Requirements

The amount of power required for a laser depends on the mateirial and the desired operation.

For example, when cutting materials like wood and plastic, consider the following guidelines for cutting:

1/8" thick requires 30w
1/4" thick requires 40w
3/8" thick requires 50 to 60w
1/2" thick requires 75 to 120w

These are rough estimates. You can use a lower powered laser to cut any thickness, but it requires more than the single pass these estimates assume.

The issue of choosing the proper laser power can be complex, so consult the manufacturer's representatives to see what will work best for your application.

Smoke and Toxic Fumes from Laser Cutters and Engravers

Lasers work by heating the material they're cutting or marking. When cutting the material is typically vaporized or turned completely into gas by the heat of the laser.

Most materials will produce smoke and sometimes toxic fumes when this is done. Consequently, it is often important to provide positive ventilation to carry the fumes outside via blower.

Mill and Mini CNC Engraving Machines

Any CNC Milling Machine can be used as a CNC Engraving Machine. Some are better at it than others.

One of the issues that will determine how good a CNC Machine is for engraving is the maximum spindle speed. Engraving Tools tend to be quite small in diameter and a lot of the materials being engraved are quite soft.

Both small diameter and softer materials leads to higher spindle speed requirements for cnc engraving.

If your milling machine lacks a high speed spindle, you may find it's worthwhile to add a sub-spindle if you do a lot of cnc engraving work.

Bosch Colt Router attached as a high speed sub-spindle...

Here are a couple of articles about that:

Austin Barnett’s Awesome Custom CNC Car Badges: Austin attached a trim router as a high-speed sub-spindle to his Bridgeport CNC Mill.
High Speed Secondary Spindle: A scrapbook of high speed sub-spindle projects others have fabricated.
Easy Multiple Spindle Options in G-Wizard: This article tells how a $400 sub-spindle made a job finish 6x faster. Quite an improvement!

Router Engraving

CNC Routers can be great engraving machines. Typically they have a large bed, and they're fitted with a high speed spindle. For more on CNC Routers, check out our Wood CNC Machine guide.

Engraving Tools: V-Bits, Drag Engravers, and Such

The typical cutting tools used for cnc engraving are V-Bits, small Ballnose End Mills, and Drag Engravers:

Metalworking tool with pointed tip and cylindrical body.

Floating Tool Holders for Engraving

Engraving can be very sensitive to surfaces that are not completely flat. You could just surface the area to be engraved with a fly cutter before the engraving process. But, another way to compensate is to use a floating tool holder for cnc engraving: