Chapter 2: Before Modeling

Before we begin the modeling, let us explain some of the properties of the laser-cut model we will be using, which are different from those of ordinary kit models.

(1) Removal of burn marks

As you know, processing parts by laser cutting leaves burned marks on its cut surface, which must be removed by grinding, especially for parts exposed after assembly. However, since simply grinding the part will result in smaller dimensions, this model has an even grinding allowance on all or part of the cut surface, depending on the thickness of the part and its usage conditions. The red line in [Fig. 2-01] shows it. The amount of grinding is about 0.1 to 0.4 mm, depending on the plate thickness, and is uniform, so grinding itself does not require excessive effort. The machined pieces have at least 0.5 to 1 mm of excess wall and are non-uniform, so we had to be careful in shaping them. This uniformly added grinding allowance is called the offset and is specified for each part in the Offset folder on the DVD.

(2) Squareness correction

Another issue with laser cutting is that the cutting width differs slightly between the front and back surfaces of the board due to minute power differences caused by the distance the laser beam reaches, resulting in the cut surface not being perpendicular (at right angles to the surface).

This is not negligible when thicker plates are used, as in the case of structural models, but the addition of offsets, mentioned earlier, is also used to eliminate this weakness. Especially on straight parts, right angles can be restored by grinding burn marks, using a right-angle shaping jig (as shown in the guidebook) as shown in [Fig. 2-02]. The use of a micro belt sander, which is not affected by the size of the curvature, is also effective for curved surfaces such as frame parts, especially those with many concave parts [Fig. 2-03].

(3) Inverted joining of parts

On the other hand, this model uses burn marks without grinding to simulate tar filling on the joint surfaces of parts. This includes frame parts and keel joint surfaces. However, if the joints are left as they are, there will be a diagonal gap between them, so either of the adjacent parts is designed to be inverted in advance and then inverted again during assembly to align the surfaces firmly [Fig. 2-04]. Parts with inverted shapes are also marked with their part IDs inverted, so it is easy to identify which parts are inverted parts (turned over again during assembly).

(4) Printing correction of large size drawings

In the modeling process, we frequently refer to prepared assembly drawings, etc., and take measurements. At this time, when large sized drawings such as assembly drawings are printed on a home printer, the figures are printed slightly larger (or smaller) than the actual design dimensions due to the printing accuracy of the printer. For example, this model has a total length of about 500 mm, and a printer accuracy of 0.2% would result in a deviation of about 1 mm. When using printed drawings for dimensional measurements, etc., the error cannot be ignored and must be compensated for. When printing a PDF file, there is a size option called "Custom Scale". By selecting this option and specifying a scale of 99.8% (or 100.2%), for example, the file can be printed to almost the actual size [Fig. 2-05]. This error can be ignored for parts drawings that can be printed in letter size.