Parent Category: Big Blue Saw Blog
Created: Wednesday, 25 May 2016 20:45
Written by Simon Arthur
Words have power, doubly so after they've been blasted into quarter inch thick stainless steel.
Imagine you're making a waterjet cut sign out of metal and want to have lettering as negagive space (holes). (This is the 2nd type of sign shown in our article on turning logos into signs.) Or perhaps you're making machine parts and just want lettering to identify your company.
You've got to choose the right font for your lettering. Not every font works equally well with waterjet cutting. Consider this if you need us to match a particular font for your coroporate identity or design guidelines.
Here you can see a typical serif font, Liberation Serif, in a variety of sizes from 16 point (about 1/8 inch tall for the capital letters) to 72 point (capitals about 0.57 inches tall). As the name suggests, this font has serifs, those tiny little flags that hang off the end of every line.
Even at the 72 point size, the detail is just too fine to be cut by the waterjet stream, represented in this diagram by the tiny red dot. The waterjet cutting stream is about 0.04 inches (1 mm) in diameter. In this diagram, the white area represents solid material, while the black area is the negative space, or hole, where the waterjet will cut out.
At 100 points (0.8 inches), shown below, the waterjet stream can barely reach into the serifs.
Below, at 200 points (1.6 inches), we now have enough room for the waterjet stream to reach into the serifs and do a good job representing their shape. Again, the red dot represents the size of the waterjet cutting stream, which places a limit on the amount of detail that the waterjet can create.
Let's compare that with Liberation Sans, a sans-serif font in the same family. At 72 points, the waterjet stream can reach most of the areas of the letters, with the exception of a few narrow spots like the lower section of the "a". It might be possible to fix this type of area up manually. Also note that the square corners of the letters will have to be rounded off. This is seen in the next image.
At 100 points, the waterjet stream can now reach all points of the lettering except the sharp inside corners. This is less than half the size needed for the serif font.
The size at which it becomes practical to waterjet cut will depend on the exact geometry of the font used, but most serif fonts are not practical below about 1.5 inches tall and most sans serif fonts are not practical below 0.5 inches tall.
When you're designing lettering, please keep in mind that certain letters will require bridges in order to connect the center of the letters to the outer part, like the lowercase "a". In typography, this area is known as a closed counter, but at Big Blue Saw we refer to this type of shape in any part as an island.
Bridges can often reduce the space available for the waterjet stream. In this example below, bridges have been added to the "b", "e", and "a". You'll notice that the ends of the top half of the "e" are quite narrow and will be rounded off. This is with Liberation Sans 100 point (about 0.8 inches tall). The bridges shown here are about 0.1 inches wide, near the minimum of what I'd recommend.
If the font is too small, the bridges can make the text harder to read. Here's the same bridging done on a 72 point font:
In general, bridges should flow with the natural strokes of the letter for the best appearance.
There are other ways to do it, though. You could do all horizontal bridges, and have them aligned as closely as is practical. Note here that the shape of the "a" does not allow the bridge to be aligned with the bridges on the "b" and "e".
A common variant on this is to add bridges through all the letters, even those without islands, to provide consistency.
Vertical bridges centered on the island area are another popular choice.
I do recommend at least 2 bridges. This allows for maximum stability when the parts are cut and during handling. As I mentioned, the minimum size you should consider are around 0.1 inches wide, but this will vary depending on the material and size of the island. Larger islands will need more bridges. Thinner material will require wider bridges to support the island.
Below you can see a few more ways that the letters could be bridged. Create your bridges to look good and hold the islands in place based on the type of material and the font you're using.
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