More thoughts on chisels
Now that I have a little more time to sit and think and type..
First of all, I own and use different chisels for different jobs. The Exacto chisel blade is ideal for situations where I need a very thin blade, as when slicing parts off a sprue, chopping bits of styrene to length, or working in between two pieces. Its small size is also handy for finer work. Though I have not done so, you can easily modify an Exacto blade with a Dremel tool, making a narrower blade for really tight spots.
On the other hand, shaving something like a lagging band or cast-on sand line off of a plastic boiler requires control, and that's easier with a more massive and physically larger tool. For that, I pull out my 1/2" woodworking chisel. I have not figured out if it's just the larger size (which fits my hand much better and gives me better control), or the quality of the steel, or the thicker, stiffer, heavier blade, but whatever the reason I find it does a much better job than the Exacto blade.
Whatever blade you are using, there are a few techniques, tricks, and rules which will help you do a good job and prevent your fingers from leaking, or worse. Some I've mentioned elsewhere and am restating for completeness, others I've failed to mention.
- Always maintain a sharp edge. A dull blade will not cut smoothly, and requires enough force to put you and your models at risk.
- Let the blade do the work. Your job is mainly to guide the edge, not jam it full force into the model. If you're pushing much harder than you'd push a pencil, you're pushing too hard. Remember that you lose fine control as you use more force, so things are less likely to go wrong if you are gentle.
- Take small cuts. Removing a large detail or area may require multiple passes with the blade, shaving a little off at a time. Smaller cuts require less effort, and are much easier to control.
- Work into a corner if possible. When a woodworker wants to cut a notch in a piece of wood, he first makes a plunge cut into the surface to make the edge, then shaves into that cut, and repeats the process as needed. Working into a corner like that helps to stop the blade from heading off in a new direction as it emerges from the work, and also keeps the slicing cut from going too far. If you must cut without a stop (such as when shaving off a grab iron), take extreme care not to use too much force, especially at the end of the cut.
- Never put a body part or any other critical item in the path of the blade. Think about what will happen if the blade slips - if there's flesh down wind, it will find it. Fortunately, a sharp blade makes a cut that heals well, usually.
- Slice rather than chop. Hold the blade at a slight angle to the direction in which you want to cut, and move it in a sideways motion past the cut. Rather than chopping plastic off, you're slicing it cleanly. This gives you better control and makes a smoother cut.
- Sharpen your blade with slightly rounded edges. This will prevent the corners from digging into the surface around whatever you're working on.
- A chisel held perpendicular to the surface makes an excellent scraper, and can remove very fine shavings to dress a surface. After slicing off a detail, turn the blade perpendicular, with the back toward the direction you want to go, and lightly push or drag it across the surface until the last remnants of the detail have disappeared.
- A chisel will go in the direction of the face closest to the surface. Hold the back flat against a model to slice cleanly, parallel with the surface. Put the bevel flat on the surface to do the same, but with the handle at a more convenient angle. If you raise the handle beyond that, the blade will tend to dig into the surface.
I've mentioned sharpening, and I mostly covered it earlier. While you can get quite fancy sharpening a blade, simple wet/dry sandpaper is more than sufficient. For the dedicated, multiple grits can be glued to a piece of glass. I normally use a loose sheet of 600 grit on my workbench, working near the edge in order to flatten the back. It takes a little time to get used to sharpening a blade - the key to making the bevel is to work as though you were going to slice something off the surface of the paper, working the entire bevel at one time. A circular motion is faster, but can round the entire edge if you're not careful. After sharpening the bevel, there will be a thin lip at the edge. That can easily be removed, and the back dressed, by laying the blade perfectly flat on the sandpaper and moving it in a circular motion. When you're done, you should have a blade with two perfect planes intersecting at the edge, both reasonably polished, and the edges very slightly rounded.
You can also change the angle of the bevel, if you like. A sharper angle will slice with less effort, but will dull more quickly. Conversely, a wider angle will be more durable, but will require more force. Personally, I have found that the factory angle is an excellent compromise and have never felt the need to change it.
