Metalwork - Materials - Working with Acrylic
In the metalwork room you will mainly be working with Acrylic, which you will probably call Perspex™. You may also work with some Nylon, but not near as much. In this section we concentrate on the techniques of working with Acrylic, but the techniques can also be used with other Polymer materials. Below is a list of the topics covered. Acrylic is available to you mainly in sheet form. The usual sizes that you will work with are 3mm, 5mm, 6mm, and 10mm. 3mm Acrylic is the best for bending or forming, as the other common thicknesses tend to melt or burn at the edges before the whole thichness of the piece is soft enough to shape. When you first get some Acrylic to work with it is usually covered with a thin plastic sheet cover. You should leave this on as log as possible as it protects the surface of the Acrylic from scratching. Take care when marking out the Acrylic, you can use a fine tip permanent marker or a Scriber. Always use Soft Jaws in the Bench Vice when you are using Acrylic, again to prevent scratching the surface.
When you wish to remove over 5mm from your piece you should hacksaw the excess away. Any measurement under 5mm and you should file. The reason for this is that if the hacksaw is not tensioned properly, or if you are not great at cutting a straight line you may accidently cut over your marking line, ruining the piece. As Acrylic is reasonably brittle you shoud keep the line that you are cutting as close to the jaws of the Banch Vice as possible. If you do not do this the Acrylic may crack or break. Cut with steady, slow, long strokes of the hacksaw and do not apply too much pressure; the teeth of the hacksaw will do the cutting for you. If you feel any vibration in the Acrylic then the line you are cutting along is too far from the Bench Vice or you are cutting too fast. If the shape you require is curved or intricate then you should use a Coping Saw, Fret Saw or a Tension File.
File the piece of Acrylic if you have less than 5mm to remove or if you want to finish off the cut. Good sharp files work well with Acrylic and a Double Cut File works the best. Again hold the workpiece as close to the jaws of the Bench Vice as possible, and use long, steady strokes. Be carefull as you may be surprised at how much material is removed by the file, especially if this is you first time working with Acrylic. When you are finished filing and you want to get a good surface finish on the Acrylic you should draw file, the edge, followed by using Emery Paper. This will remove the marks left by the file. Finally to get a perfectly smooth finish use a metal polish such as Brasso™ or a special Acrylic polish.
Be very careful when drilling Acrylic, as you may either crack or break the piece, or injure yourself. Because the Acrylic will bend easily make sure that you have the workpiece supported or held reasonably close to the point to be drilled. You should also put a piece of wood of an appropriate size beneath the, as shown below. Acrylic When drilling use a high speed and a light feed. If you press the drill too hard you will bend the Acrylic or cause it to punch through and chip the backside of the piece. Your teacher may have a set of drills with a Point Angle of 140°, which is better for drilling Acrylic, so check it out. The standard Point Angle of 118° tends to catch the Acrylic, which may pull the piece from the vice. Don't drill Acrylic and metals at the same time as the heat generated by the drill bit cutting through the metal may melt the Acrylic
You can join Acrylic using screws, nuts and bolts, however here we are looking at the Bonding of Acrylics using cements, solvents, and adhesives. Cements will fill gaps usually, and so are good to use if the surfaces to be joined are not that smooth. They also tend to be quite strong. Solvents such as Chloroform and Ethylene Dichloride, melt the surfaces to be joined so that they will stick together. They will not fill gaos so your work must be very smooth. You should also use something like masking tape to cover the areas close by that are not to be joined in order to prevent surface damage to these areas. Remember solvents are dangerous and so should not be used without the greatest care. They should also be used in well ventillated areas. Finally Adhesives, are glues. One type that works well is Superglue™. The surfaces to be glued should be gently scratched with emery paper befor gluing. Be very careful with Superglue™, use gloves as it will stick the skin on your fingers together.
If you wish to bend your piece of Acrylic then there are a number of methods depending on wheather it is a thin bend or a wide one. For a thin bend it is best to use Strip Heater which you should have in the metalwork room. Hold the piece of Acrylic with gloves as it can get quite hot. Do not let the Acrylic touch off the Strip heater as it will burn. You should turn the piece over regularly so as to heat the Acrylic through properly without burnign one side. In order to shape the pieve you can then use ready made jigs, that the teacher might have or pieces of metal. Allow the piece of Acrylic to cool before continuing to work on it.
If you wish to heat up the Acrylic for large bends you are probably best to heat up the whole piece in the oven. An ordinary kitchen oven will do and a temperature of between 60°C and 70° will do. You will also need glowes, tongs and a piece of cloth with pieces of wood stapled to the ends. It is a lso a very good isead to made a former that could be held in the Bench Vice so that you can bend the piece of Acrylic around it.
Forming is the same as Bending except in this case you always heat yp the piece of Acrylic in an oven. You also need a Punch and Die. The Punch and Die are opposite in shape and fit into one another. When you heat up the piece of Acrylic you then place it in the Die and use the Punch to force the piece into the Die. Hold the Punch and Die together until the piece of Acrylic has cooled.