You can easily create curves and bends in flat acrylic or plexiglass sheets for your models or miniatures. The tutorial which follows shows how you can make bends with a simple jig and common heat sources. Most scale models won't need bends in acrylic more than 1/16 inch thick. The difficulty with small projects, having tight bends close together, is control of the heat source so the adjoining curve isn't affected.
To create bends for small-scale projects in plexiglass (perspex) or acrylic 1/8 inch and thinner, you can use a small torch (butane kitchen torches work well), a paint stripping heat gun, or an embossing heat tool, which is a wand that works very similarly to a paint stripping gun, but using a smaller more directed heat flow with a smaller fan. Using these instructions, a modeler can bend anything from paperweight sheets of acrylic, up to 1/8 inch thick material, in sizes suitable for most miniature projects.
Tools and Materials Needed to Make Simple Bends in Sheet Acrylic and Plastic
To Bend Sheet Plastic and Acrylic You Will Need:
- Heat Source - Small projects with bends that are close together will need upon heat source which can be easily aimed at small areas. The two best tools for this are a small butane torch, the type used in the kitchen work well, or you can also use an embossing heat tool, used by card makers and scrapbookers to melt and apply embossing powders. For larger projects, it is possible to use a heat gun, of the type used by airplane modelers to apply shrink plastic coatings, or a paint stripping heat gun or regular propane torch. Hair dryers will not achieve the level of heat required for anything more than very thin sheet acrylic and will move too much air to be of much use working with thin materials.
- Clamps - We like using quick release bar clips but you can use anything that will hold your scrap strip wood in place as a bending jig.
- Scrap wood - You need a straight-edged piece of wood for your jig; we suggest something at least 1/8 inch thick and wide enough for your clamps. You will also need spacers the same thickness or slightly thinner than the plastic you need to clamp, to keep your stripwood jig even with the top of the plastic you will be bending. You also need a heatproof work surface or a scrap of MDF or plywood to act as a work surface you can clamp your bending jig to.
- Plexiglass or Acrylic Sheet - This system works well for small pieces of plexiglass in thicknesses of up to 1/8 inch. For thicker acrylic, you will need to use a metal bar clamped very securely, and you may only be able to work with narrow strips of material as your heat source may not be able to heat wider areas of thick material.
- Protective Equipment - Hot plastic can be dangerous. Always work in a well-ventilated area away from flammable materials, other than those you will be working with. Wear eye protection, and use welding gloves or kitchen oven gloves to protect your hands from burns.
Some types of sheet acrylic are sold as heat withstanding, or plastic which can be embossed from stamp and scrapbook stores. These types of plastic will not bend when heat is applied. Avoid sheets of thin plastic/acrylic which claim to be 'embossable'.
Set up Plastic or Acrylic Sheet in a Simple Bending Jig
To set up your plastic or acrylic sheet to bend simple curves for your miniature and model projects you need to first remove the protective covering from the material you wish to bend. Use long thin (1 inch or so in width) test strips to practice your technique and learn how your particular heat source affects your chosen thickness of plastic.
Lay your plastic on your heat safe work surface and place a scrap of stripwood over your plastic roughly 1/4 of an inch in front of where you want your bend to be. This will be somewhat determined by the thickness of your plastic. Thicker plastic will need a wider radius curve for most bends. Use a ruler to check that your sheet of plexiglass or plastic is held squarely clamped beneath your stripwood jig. The stripwood will restrict the application of heat (it will catch fire if you overheat the wood) and will prevent the plastic beneath it from becoming soft enough to bend.
If possible, leave a long end of your plastic strip where you can easily push up on it with a hand protected by a welding glove or oven glove. It is far easier to bend the long end of a plastic strip than the short end. Make sure any flammable or heat sensitive material on your clamps is well away from where you will be applying heat to your plexiglass.
How to Make a Successful Straight Bend in Sheet Acrylic or Plastic
With your sheet plexiglass clamped securely to your work surface under a straight edge that defines where the bend will be, it is time to heat your material. The object of heating the sheet is to heat it evenly along a line just in front of the straight edge of your clamped jig. To make sure you apply heat evenly, pass your heat source at an even, slow speed along the line of plastic in front of the jig, keeping it far enough away that the heat source will not singe your wood jig. Try to keep the heat source at a right angle to your sheet of plastic/plexiglass. If you turn your heat source as you pass across the acrylic, the heat won't be evenly applied across the entire width of your sheet.
While you are applying even heat along the bend line, press gently upon the sheet of material you are bending. There will come a point when the material will move easily upwards as it reaches a molten state. You should be able to feel this point evenly along the full width of the strip you are bending. It should not be softer on one side than on the other.
When you feel that your sheet is allowing you to push up evenly on it, remove your heat source and set it safely aside on a stand or heat resistant surface; the end of your tool will be hot! Holding the sheet material evenly with both hands (both in protective gloves) push the sheet up gently bending it against the line of the jig as shown in the photo above. You must use two hands to do this with even pressure, or your material will twist slightly as you bend it, unless you are working with a very thin, narrow strip.
When you have your sheet at the correct angle or have bent the curve you want (for a window or the front of a curved bakery case, which may not be at 90 F), hold the plastic gently in place for a few seconds until it sets up again. Allow it to cool still clamped in the jig as shown.
You can use the same heat tool you use to bend plastic, to seal and neaten the cut edges of any plastic parts. Run your heat tool gently back and forth along a cut plastic edge to soften it just enough that it turns clear.
Problems When You Bend Incorrectly or Before the Material Is Soft Enough
In the photo on this page, you can see a poor bend in a sheet of 1/16 inch thick plexiglass. The bend is 'kinked' and not even, and is too far away from the jig, so it is not straight and square with the end of the material.
The problems with this bend were caused by not applying the heat source close enough to the jig, and bending the material before the material was evenly softened across the entire width of the material. You must wait until the moment when you feel the material 'slump' as you have no way of measuring the heat. When you are applying upwards pressure on the end of your acrylic, you will feel it start to move against your hand, then it will move very quickly. That free point when the material is able to move quickly is when you want to shape it against the jig. If you start trying to force it before it is fully softened, you will not get as even a bend, as it will be soft in some areas but not others along your bend line.
Problems Caused by Overheating Sheet Acrylic - Bubbles and Scorching
If you don't apply heat evenly to the bend line of a sheet of plexiglass or acrylic you can create bubbles or scorch marks which cannot be removed. Do not keep your heat gun or torch too close to the plastic. If you are singeing the wood on your jig, you are too close!
If you find bubbles or scorch marks occurring in your test bends, try to move your heat a bit faster along your bend line, or hold it further away from the surface of your sheet material. The distance and speed will be different depending on the thickness of the material you are working with.
Twisted Bends Caused by Uneven Pressure When Bending Sheet Acrylic
The photo on this page shows a test strip of sheet acrylic which did not bend evenly along the line of the jig. This is the same strip shown in the jig where the heat was applied too far away from the bend line and applied unevenly. The bend was made before the material was evenly softened, and this resulted in an angled rather than a straight line bend. The material on one side of the strip was not quite ready to bend fully when the bend was made. This resulted in an angled rather than a straight bend against the jig.
Making Even Bends in Paper Thin Acrylic or Plastic Sheet With a Simple Jig
You can make bends of all types in very thin sheet acrylic, provided you work out the heat and time required for bending thin material and do not pass that point. Thin sheets are easily warped quite far away from the bend. For thinner sheets, you need to apply heat evenly to a very narrow line of the material. If you do not have a heat source that will work for thin materials, try the method shown for heat welding plastic, using a metal kitchen spatula or blade heated against an iron, then pressed against the material.
The paper-thin acrylic sheet shown here was bent with an embossing heat tool, which was easy to control above the jig. Across a wider section of material, even heat application would be difficult to achieve without causing the material to warp. Using a heated blade would be a more reliable method.