Raspberry Pi Retro Gaming by Mark Frauenfelder & Ryan Bates

Author:Mark Frauenfelder & Ryan Bates
Language: eng
Format: epub
ISBN: 9781484251539
Publisher: Apress

The Birch (left) has a smooth, uniformly sanded finish of, well, Birch plywood. The underpayment plywood (right) has a somewhat smooth and somewhat uniform surface.

Flipping these samples over (ignore the burn marks from the laser cutter), Figure 5-4 presents a clearer detail of what we are paying for. The Birch sample (left) maintains a finished veneer surface.

Figure 5-4Underside of birch and underlayment plywood

In contrast, the underlayment shows the veneer inconsistencies of some sort of hardwood; these are the knots and likely to be in abundance in lower-grade plywood especially for subfloor plywood. Because of their hardness, these knots tend to fall out during the shaving process that creates the veneer layer. This knot (and every knot) is slightly recessed and presents as an imperfection that would have to be filled prior to painting either with a wood-type or paintable filler.

Let’s look at a cross section of these samples shown in Figure 5-5. Birch plywood is on the top and the underlayment is at the bottom. The Birch veneer is much thicker than the underlayment veneer. The inner ply is also much denser and uniform and is likely genuine wood (note the wavy, ring layer passing through). The underlayment (bottom) has a barely visible veneer which is prone to chipping. Sand this too much and you’ll break into the middle plywood layer. The middle ply is usually a wood/paper/filler mix. This nonuniform layer is not bonded together nearly as well as the higher-grade plywood and can sometimes cause issues on small intricate laser-cut parts. There are also more void present in the underlayment, which is again acceptable for the grade of plywood (subflooring). These live edges can be unreliable when painting and finishing unless you have a good body/wood filler that primes and bonds the surface.

Figure 5-5Cross section of birch and underlayment plywood

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