With Wings As Eagles: Craig P. Steffen's Blog

do not underestimate cutting concrete

2009 October 04 20:59

Getting there. Picked up a circular saw and a masonry blade.

To review, here's what we're doing. I have a triangular concrete pad that I'm going to put tile on top of:

what I want to do is have the hexagonal tiles match as straight possible against the straight edge on the left of the triangle above. I also want the points of the hexagon agains the right edge, so that they'll sort of run straight along the dirt edge. The angle at the bottom point of the triangle is 45 degrees.

I thought I figured out how to make the tiles line up, but it will require cutting some of the tiles. Here's a diagram where I tried to figure out how to make the angles fit into the 45 degree triangle.

In this diagram, I want the purple edge to run along the right side of the triangle above. The sum of the red and the green angles is 60 degrees. The question is how close to 45 degrees is the green angle. So I'll figure out what the red angle (I call it phi) is and subtract it from 60.

Here's the expression to find the phi angle.

This no problem with a scientific calculator. However...Jasper is being cuddly and doesn't want me to get up.

So instead I decided to see of Google's math parse is up to computing this equation. It can, as it turns out.

So the phi angle is 16 and a fraction, so the corner formed will be a tiny bit less than 44 degreees. The question is, is that close enough to 45? Will that fit Ok?

Here's a trick:

For small angles, say, less than 10 degrees, the far end of a triangle (red line) is 1/60 of the length of the triangle (either green line) per degree in the small angle (purple arc). So for my triangle, the angle of the tiles is going to be about one degree less than the ideal of 45. The sides of the triangle of the concrete pad are 78 inches, so it will be off by a little more than an inch on the far end. I think one inch off at the far end is fine for this construction, so that will do.

So now we make the diagram a reality. So I bought a masonry circular saw blade, and I put in in the circular saw to cute the tile. Some things to that I'd forgotten about drilling/grinding concrete: - Concrete makes an incredibly fine dust that gets in and on everything. I don't know if it's specifically harmful, but it will certainly irritate your nose, mouth, and lungs. - Cutting concrete takes a very very long time. - It's pretty loud.

At the end of the process, I got the piece sliced off.

So here's a test fit:

In the right corner, the two pieces marked by purple spots are the two parts of the tile that I cut. They're fitted into the corner as will be in the final configuration.

Aa little farther to the left, you can see the tile that overlaps the bricks on the edge. The triangle outlineed in red dots will be cut out of that tile, the piece will be turned around and fit into the hole outlined by the green dots.