Begin by cutting off a 10-in. length of the board and setting it aside. Rip the remaining 38-in. board to 6 in. wide and cut five evenly spaced saw kerfs 5/8 in. deep along one face. Crosscut the slotted board into four 9-in. pieces and glue them into a block, being careful not to slop glue into the saw kerfs (you can clean them out with a knife before the glue dries). Saw a 15-degree angle on one end and screw the plywood piece under the angled end of the block.
Just as a bit of an aside, I’m fairly new to woodworking and I’ve been looking into some CNC routers for cutting for these projects. I came across something interesting. The guy on this page claims to have put together a homemade CNC router for less than $300. I’m curious to know what you think about it. If you’ve never heard of it and don’t have an opinion, then no problem; I thought I’d ask anyway.
Here’s a traditional Swedish farm accessory for gunk-laden soles. The dimensions are not critical, but be sure the edges of the slats are fairly sharp?they’re what makes the boot scraper work. Cut slats to length, then cut triangular openings on the side of a pair of 2x2s. A radial arm saw works well for this, but a table saw or band saw will also make the cut. Trim the 2x2s to length, predrill, and use galvanized screws to attach the slats from underneath. If you prefer a boot cleaner that has brushes, check out this clever project.