Make: Electronics by Charles Platt (classic books to read TXT) 📗

textured on one side, which is the side that should face outward, as it is more scratch-resistant than the smooth side.

Because you won’t be adding paint or other finishes, you’ll have to be careful not to scuff the plastic or scratch it while working. Clean your bench thoroughly before you begin, taking special care to remove any metal particles, which tend to become embedded in the plastic. Use wooden shims in the jaws of your vise, and avoid resting the plastic accidentally on any sharp tools or screws. Working with ABS requires a clean environment and a very gentle touch.

Cut with Care

You can saw ABS, but if you use a table saw, the plastic will tend to melt and stick to the blade. These smears will get warm and sticky when you feed the next piece of plastic into the saw, and the result will be extremely unpleasant. The whirling blade will grab the plastic and hurl it at you powerfully enough to break bones. This is known as “kickback” and is a very serious risk when sawing plastic.

If you have extensive experience using a table saw, you are actually more vulnerable, because the reflexes and cautions you have developed while dealing with wood will not be adequate for working with plastic. Please take this warning seriously!

Your first and most obvious precaution is to use a plastic-cutting blade, which has a larger number of thicker teeth to absorb the heat. The blade I have used is a Freud 80T, but there are others. If you use a blade that is not suitable, you will see it starting to accumulate sticky smears. This is the only warning you will get. Clean that blade with a solvent such as acetone, and never use it for ABS again.

Regardless of other precautions, always wear gloves and eye protection when using a table saw, and stand to one side when feeding materials into it. Personally, after one episode of kickback that I thought had broken my arm, I prefer not to use a table saw on plastic at all.

For long, straight cuts, the alternatives include:

Panel saw (big and expensive, but safe and accurate).

Miniature handheld circular saw with a blade around 4 inches in diameter, guided with a straight edge clamped to the sheet.

Hand saw. This is my old-school preference. My favorite is a Japanese pull-to-cut saw, which makes very clean cuts: the Vaughan Extra-Fine Cross-Cut Bear Saw, 9-1/2 inches, 17 tpi (teeth per inch). If you use one of these, be careful to keep your free hand out of the way, as the saw can easily jump out of the cut. Because it is designed to cut hard materials such as wood, it has no difficulty cutting soft flesh. Gloves are strongly recommended.

Figure 5-76. The perils of kickback. Plastic easily sticks to the blade of a table saw, which will hurl it at you unexpectedly. Use other tools to cut plastic.

Curving Cuts

Curving cuts involve relatively little danger, although eye protection and gloves are still advisable. My preferred tools:

Band saw with a 3/8- or 1/4-inch blade designed for thin wood or plywood.

Jigsaw. I have a special liking for the DeWalt XRP using Bosch blades that are designed for hardwood or plastic. This will cut complex curves in ABS as easily as scissors cutting paper.

No matter what type of saw you use, you’ll have to clean ragged bits of plastic off the cut afterward, and the absolutely necessary item for this purpose is a deburring tool, available from http://www.mcmaster.com and most other online hardware sources. A belt sander or disc sander is ideal for rounding corners, and a metal file can be used to remove bumps from edges that are supposed to be straight.

Figures 5-77 through 5-80 show various cutting tools. Figure 5-81 shows a deburring tool, and Figure 5-82 shows a disc sander.

Figure 5-77. A band saw is an ideal tool for cutting complex shapes out of ABS plastic. You can often find them secondhand for under $200.

Figure 5-80. This DeWalt jigsaw can run at very slow speeds, enabling precise and careful work with plastic.

Figure 5-78. A handheld circular saw, running along a straight-edge, is much safer than a table saw for cutting plastic, and can produce comparable results.

Figure 5-81. A deburring tool will clean and bevel the sawn edge of a piece of plastic in just a couple of quick strokes.

Figure 5-79. This Japanese-style saw cuts when you pull it, rather than when you push it. After some practice, you can use it to make very accurate cuts. Because ABS is so soft, minimal muscle-power is required.

Figure 5-82. A belt sander or disc sander is the ideal tool for rounding corners when working with ABS plastic.

Making Plans

I like to use drawing software to create plans, and I try to print them at actual scale. I tape them to the smooth side of a piece of white or natural-color ABS, then use an awl to prick through the plan into the soft surface beneath. I remove the paper and connect the awl marks by drawing onto the plastic using a pencil or a fine-point water-soluble pen. Its lines can be wiped away later with a damp cloth. Don’t use a permanent marker, as the solvents that you will need to clean it may dissolve the plastic.

Because ABS will tend to open a fissure when you bend it at any inside corner where you don’t have a smooth radius, you need to drill holes at these locations, as shown in the cart plans in Figure 5-92 on page 275.

A regular half-inch drill bit is too aggressive; it will tend to jam itself into the plastic within one turn of the drill. Use Forstner bits (shown in Figures 5-83 and 5-84) to cut nice smooth circles.

Figure 5-83. A Forstner drill bit makes clean, precise holes; a large regular drill bit will chew up ABS