Using a circular cutter
I have used a circular cutter to make 180 degree cuts in 0.040 inch styrene sheet for a couple of tunnel portals that I will install on my N scale model railroad. The cutter is made by Olfa, and I purchased it at a local art supply store rather than a hobby shop that sells train stuff. Art supply stores sell lots of tools, paints, craft items, and materials useful to a model railroader. The circular cutter has a strong, sharp compass point that is mounted on a sturdy head which has an adjustment screw. By loosening the screw, a horizontal beam can slide in or out a variable distance from the center point and then be locked down at the desired distance. The replaceable cutting blade (held into place by another screw) is mounted on the horizontal beam.
Nobody makes an N scale tunnel portal the size and shape that I want, so I had to cut my own. The tunnel opening has a radius of 8 ½ scale feet from the track center line, so that is what I set on my circular cutter. The straight vertical dimension for each side is 20 scale feet above the top on the rails plus another 3 feet for the height of the rails, crossties, and roadbed. Both of the vertical sides have to be exactly tangent to the semicircle above, so determining where to position my straight edge for the first side was the trickiest part of the whole project. From that line, I used a steel drafting triangle (also purchased from the art supply store) to place the cutting point and center compass point. I swung a 180 degree arc to locate the position of the other vertical side. My N scale ruler (shown here) is 10 scale feet wide, so my first vertical cut was 10 scale feet from the edge of the styrene sheet. After the circular cut and both vertical cuts were completely through the plastic, I could easily remove the excess from each side.
Figuring the geometry of where to position my circular cutter and the straight edge to guide my razor blade required a lot of thought before doing any of the actual cutting. Once I began cutting, I had to be careful to keep my blades in the right places, but the cutting itself was very repetitive and time consuming. Each tunnel portal required an hour or two of MANY short, little cuts before I broke through the plastic sheet. Then there was sanding to smooth it out and trimming the overall piece to fit the future mountain that I haven’t built yet. This photo shows the positioning of the circular cutter, but I took the photo after the job was done (and my nails repainted). For all this cutting, I used my Dupli-Cutter to hold my work in place. The Dupli-Cutter has clamps that can be positioned in several places, an adjustable slide sheet held down by the clamps, and a frame whose jaws can be opened up to hold various thicknesses of plastic for making precise, square cuts.
Using a circular cutter
I have used a circular cutter to make 180 degree cuts in 0.040 inch styrene sheet for a couple of tunnel portals that I will install on my N scale model railroad. The cutter is made by Olfa, and I purchased it at a local art supply store rather than a hobby shop that sells train stuff. Art supply stores sell lots of tools, paints, craft items, and materials useful to a model railroader. The circular cutter has a strong, sharp compass point that is mounted on a sturdy head which has an adjustment screw. By loosening the screw, a horizontal beam can slide in or out a variable distance from the center point and then be locked down at the desired distance. The replaceable cutting blade (held into place by another screw) is mounted on the horizontal beam.
Nobody makes an N scale tunnel portal the size and shape that I want, so I had to cut my own. The tunnel opening has a radius of 8 ½ scale feet from the track center line, so that is what I set on my circular cutter. The straight vertical dimension for each side is 20 scale feet above the top on the rails plus another 3 feet for the height of the rails, crossties, and roadbed. Both of the vertical sides have to be exactly tangent to the semicircle above, so determining where to position my straight edge for the first side was the trickiest part of the whole project. From that line, I used a steel drafting triangle (also purchased from the art supply store) to place the cutting point and center compass point. I swung a 180 degree arc to locate the position of the other vertical side. My N scale ruler (shown here) is 10 scale feet wide, so my first vertical cut was 10 scale feet from the edge of the styrene sheet. After the circular cut and both vertical cuts were completely through the plastic, I could easily remove the excess from each side.
Figuring the geometry of where to position my circular cutter and the straight edge to guide my razor blade required a lot of thought before doing any of the actual cutting. Once I began cutting, I had to be careful to keep my blades in the right places, but the cutting itself was very repetitive and time consuming. Each tunnel portal required an hour or two of MANY short, little cuts before I broke through the plastic sheet. Then there was sanding to smooth it out and trimming the overall piece to fit the future mountain that I haven’t built yet. This photo shows the positioning of the circular cutter, but I took the photo after the job was done (and my nails repainted). For all this cutting, I used my Dupli-Cutter to hold my work in place. The Dupli-Cutter has clamps that can be positioned in several places, an adjustable slide sheet held down by the clamps, and a frame whose jaws can be opened up to hold various thicknesses of plastic for making precise, square cuts.