Laser Cutting and Engraving

Introduction We have all probably used a lens to focus the sun’s rays onto a piece of paper or card and watched it burn a hole and/or burst into flames. Imagine a CO2 laser tube (or diode, or other device) as providing the equivalent of the sun’s rays, and a computer-controlled fast-moving lens and you have the principle behind a laser cutting and engraving machine, henceforth referred to as ‘laser’ in this article. A correctly focussed laser beam (illustrated above right) will cut or engrave a wide variety of materials.
The heat source for the laser can be provided by a number of devices. As with my previous article on 3D printing, I do not confess to be an expert on lasers, just an experienced user, nine years and counting, who has used the technology to further his railway modelling hobby. My laser is a 35Watt HPC 3020 with a usable work area of 200mm x 300mm (A4 size in old money). It is this laser I will describe in detail, but I will also mention other types of laser you might see advertised and how their performance might differ from mine. HPC 3020 CO2 laser on homemade wheeled stand which slides under my layout when not in use. The laser software 'Newlydraw' requires Windows XP which runs on a second-hand laptop shown to the right of the laser. Files are transferred using USB sticks.

So if laser cutting machines work by using a focussed source of heat to cut or engrave different materials it follows that they work by burning stuff! The first basic therefore has to be a good fire extinguisher and fire blanket. The machines are a very real fire risk and must NEVER be left unattended, even for that short loo break. My own ‘fires’ have been limited to small glowing embers of cardboard when I have had the power too high and the lines too close together. I keep a small water spray bottle close to the laser and this easily deals with these. Please take this warning seriously and ensure that if you do use a laser, your own or another's, you have the appropriate fire provention/protection equipment in place first.

The second basic is good ventilation. Most of these machines come with some sort of fan and tube to enable the fumes and toxic gasses from the cutting process (burning) to be removed. For infrequent use an open window will suffice, but the best solution is to vent through a hole in the wall. I have added a further, powerful, fan to my extraction system. This is particularly useful when cutting materials like Acrylic Sheet which have a strong smell when cutting. Other materials, like PVC, produce such toxic gasses THAT THEY SHOULD NEVER BE USED. My yardstick is ‘if I can smell it then it is doing me harm’.

Given that you have to be present whilst the laser is working, and that the process is not silent, you will also have to tolerate some considerable background noise in your workroom.

Note that the wavelength of the light produced by many laser cutters is invisible and VERY harmful to eyesight. My laser has a lid that cuts off the power when lifted, and a glazing material which filters out the harmful aspects of the laser light so you can safely watch the laser as it works. Without protection built into the machine you must wear suitable glasses to protect your eyes.

All lasers work by using a focussed beam of heat to cut or engrave a material. The source of that heat can vary. My experience is with a 35Watt CO2 laser and it is that laser I shall describe here. The laser tube is made of glass, is water cooled, and therefore you need a tank of water and a pump to circulate it. After a few hours use the water heats up and the laser becomes less effective. The larger the tank, the longer you can use the machine. I have a water chiller unit (about £300) which both circulates the water and chills it so I can use the laser all day if I need to. The laser tube lasts about 1000 hours and costs about £250 to replace, equivalent to about 25p an hour to run. The laser tube sits along the back of the machine and emits its beam into the first mirror which reflects it to a second and third mirror and down to the workpiece via a focussing lens. The honeycomb bed can be raised and lowered to focus the laser on different thicknesses of material.

The laser sits at the back of a substantial metal cabinet and the beam from it (which is invisible) is moved by stepper motors and reflected by mirrors to a lens which focusses the beam into a tiny spot on the workpiece. The worktable can be raised and lowered to enable different thicknesses of material to be focussed exactly. It is this spot of intense heat which does the work. By using more or less power the intensity of the heat spot can be varied, as can the speed at which it moves over the workpiece. Low power and fast speed will engrave the surface, high power and low speed will cut the workpiece.

To keep the workpiece cool and blow away burnt debris, a small air jet, created by a small air compressor (more noise!) blows across the cutting point.

The laser is controlled by software which will be supplied with the machine. Imagine this as similar in function to the ‘printer driver’ software which comes with a colour printer. You don’t need to know how it works, just how to use it. My machine came with a program called ‘Newlydraw’ which has very limited functions, but can read two important file types and send them to the laser.

Newer lasers will come with newer software, but I believe the principles are the same. Most lasers will read a file type known as .DXF. These files are composed of lines which the laser will follow to cut, or on low power, engrave.

The other type of file commonly recognised is a .BMP (bitmap) file such as those produced from a picture. Suitably processed a .BMP file can produce some interesting engraved results from these .BMP files.

So, you have your laser machine, a pump and water supply to keep it cool, a compressor to blow air as it works, and a fan and tube to extract the fumes, you are ready to laser.

Before you can do anything you will need a drawing of what to cut or engrave. You will either need to find a suitable drawing done by others, or learn to draw items yourself. This involves using a CAD (Computer Aided Design) program, a ‘word processor’ for drawings. If you can use a word processor to write text and have learnt how to click on an icon to create bold, underlined, or bold text, then you will be able to learn how to use a CAD program. Various icons draw various shapes and others enable these shapes to be moved and amended.

For designs which combine cut lines (.DXF files) and engraved areas (.BMP files), I use CorelDraw which can save both types of drawing in the correct format and can also ‘paint’ a texture (.BMP file) into an area such as the walls of a house such that it is possible to engrave stonework onto card and then cut it out by loading both files into the laser. Older versions of CorelDraw may be available at reasonable cost via the Internet. Developing a CAD (Computer Aided Drawing) of a window for the laser to cut out. This is done in stages shown left to right. Cut and paste of shapes can be done in a CAD program, much like cut and paste of text in a word processor. This can speed up the drawing process.
For designs which might combine laser cut and 3D printed items I use Sketchup Make which, with a suitable plug-in, can export both .DXF files for cutting on the laser, and .STL files for 3D printing. Sketchup Make is available as a free download off the Internet, as are the plug-ins required to export .STL and .DXF files.

Which CAD program you decide to use is down to personal preference. I chose by downloading five free trial programs and after spending a couple of hours on each I chose the one I felt I had made the most progress with.

Sadly there is no shortcut to learning how to use a CAD program. You have to practice. However, given a couple of hours a day for a week, most people will be able to draw simple lineside objects such as fences, gates, cable trunking, control cabinets etc., as well as simple buildings with doors and windows.

Lasers are particularly useful where many parts of the same item are required, such as window frames and doors, or even a complete terrace house repeated many times.

Cardboard is the most versatile and usable of all the materials you might cut and engrave. Mount Card, as used for picture framing, is about 2mm thick, supplied in many colours, and cuts very well on the laser with low power and reasonably high speed. It also engraves well.

For prototyping I use cereal packet which is both free and lasers at high speed. This is especially useful when the final material is Acrylic sheet as this is relatively expensive and slow to cut.Window frames cut into cereal packet card, 2mm scale. The same window frames sprayed white and incorporated into a 2mm scale warehouse building. The stonework on the walls is laser-engraved mountcard.

This type of plastic is readily available in sheets 2mm and 3mm thick and a 35Watt CO2 laser will cut it in one pass at a relatively slow speed/high power setting. Unlike a sawn edge which is rough, a laser-cut edge on acrylic sheet is very smooth and can be used for small and intricate interlocking parts such as the corners of buildings and even gears.

I use Acrylic Sheet as a structural element in G Scale rolling stock and outdoor buildings where it provides a sturdy and stable base onto which I can then glue 3D printed detailing elements. Acrylic Sheet melts and welds together like Styrene with Plastic Weld or similar glues. Acrylic sheet laser cut to make the gears for a servo-controlled level crossing.

These products do not laser cut well as the edges round and melt with the heat and detail is lost. A similar-looking material called Rowmark is available that does laser cut well and glues together like normal styrene sheet, however, it can be expensive and difficult to source. A G scale signal constructed out of laser-cut Rowmark (styrenetype material) with an acrylic sheet base housing the three servos and electronics.

For anything requiring fine detail I turn to Mylar. This is a tough plastic often used as a masking film by airbrush artists and is readily available in thicknesses from 75 to 500 microns.

To laser cut fine detail in Mylar I use a glue stick to affix it to mountcard. This keeps it flat whilst cutting and also gives you a good indication of the correct power as the cardboard is marked by the heat as the Mylar is cut. For the finest detail I use high speed and low power and do three or four passes of the laser. This avoids burning the edges of the Mylar. Detailing at the top of the columns on the building, above right, is laser -cut Mylar. The centre hole is less than 1mm in diameter. This 4mm scale building is made of several layers of laser-cut and engraved mountboard with a styrene and Mylar veranda.

These are produced in various qualities and types. Ensure you purchase ‘laserable’ varieties which are created w ith suitable glues for non-toxic laser cutting/engraving. The edges are always blackened by the cutting process. Many commercial companies use 2mm and 3mm M DF to make O gauge build ing kits, often with laser-engraved brickwork. Laser-cut super-light baseboard with a 6mm plywood top. As the laser can only cut up to A4 in size, the framing is 2mm MDF designed to overlap and is glued together making it 4mm thick.

There are many companies offering laser cutting. If you can draw your object and export it as a .DXF file, they can produce your item(s) for you. Alternatively you could investigate whether you have a FabLab or Makerspace near you. They often have laser cutting equipment which is free to use, or for hire by the hour.

The most powerful and versatile equipment for laser cutting and engraving for our hobby is the 35w/40watt CO2 laser. Bought in the UK with backup and support (from companies like HPC Laser in Elland, West Yorkshire) they currently cost from about £2,000 plus VAT. Similar-looking machines are advertised on Ebay for about £400 but often do not have the air assist compressor, and the amount of support will vary. If you know someone with a laser, or have access to a FabLab or Makerspace for support and help these may be worth considering.

A 35Watt CO2 laser as described above can produce items of ‘commercial’ quality, albeit of perhaps a smaller size and somewhat slower.

Lasers based upon laser diodes are also available, and although I have no experience of these I have a colleague who speaks highly of his 5Watt (5000 Mw) Emblaser2 machine. Even this requires multiple passes to cut through material other than thin card. Diode lasers with even less power than this are advertised on Ebay but my impression is that they will be limited to marking rather than cutting cardboard. Read reviews and look at the relevant Forums before purchase.

There are also industrial lasers capable of cutting through metal but their cost puts them outside the scope of this article!

Laser cutting and engraving machines can produce excellent commercial quality results from CAD produced .DXF files. However, the most versatile lasers have a relatively high price tag and need setting up carefully to work successfully in a domestic environment.

Before investing in a machine, ensure you will be able to make the most of it by learning CAD first.

• HPC Laser: www.hpclaser.co.uk for laser machines and materials, Rowmark type plastic
• HPC laser forum: www.forum.laserscript.net for useful advice for beginners.
• RM Web: www.rmweb.co.uk scroll down and select the laser cutting section.
• Makerspaces: Search Google for ‘makerspaces uk’ to find out about locations.
• FabLabs: www.fablabsuk.co.uk
• Hobarts: www.hobarts.com sell lasers, but good for laserable sheet materials.
• York Modelrail: www.yorkmodelrail.com sell laser cut and engraved model railway items and also offer a bespoke service to cut your own designs.
• www.stencilwrehouse.co.uk can supply polyester film (Mylar) for fine detailed work.
• Schools and Colleges also often have laser cutting equipment, so children and grandchildren often have access to these machines and may welcome a project for them.

Bob Gledhill is the author of Laser Cutting and 3D Printing for Railway Modellers published by Crowood Press ISBN 978 78500 226 7