Thursday, May 22, 2008

Making a chessboard pt 6

Tonight's adventures...

I decided that the borders of the chessboard made the it look too bulky, almost as if it was single block of oak. To remedy this, I decided to cut scallops in the bottom of the border. I'd leave "feet" at the corners but cut an arc between them.

This represents one of my four border pieces. The pink rectangular area represents the groove that the board's lip fits into. The arc at the bottom is what I want to cut. In actuality, I selected a chord of a circle, not an ellipse as drawn, but my gimp fu is weak.

Here's a pic. It's sitting on the tablesaw which might made it hard to see.

Here's another pic. Hopefully the plywood will make it easier to see.

Ok, it's a tad subtle. Compare to pictures in previous postings to see the difference. The arc/scallop is a chord of a circle with a radius of 80" or so. I didn't have a circle jig that large sitting around so I had to improvise. I decided that I wanted the arc to go from 0" deep by the feet to 3/8" deep in the center. I did all the calculations in Excel to plot several points onto my template. Then I could connect them and have a reasonable approximation of the arc I wanted. The method sucked my soul (ok, measure 3" over and 5/64" up...) I needed a less tedious way.

I marked three points on my template - the top of the arc and the point by each foot where the arc will leave the wood. I got a thin strip of plywood scrap and bent it so it passed through all three points. I made sure the strip bent evenly. I then traced the curve made by the bent strip onto the template. After cutting to the line on the bandsaw, I had a template I could use for all four borders. Worked great.

More to come!


  1. This is andy b. from HSM (you posted a link here for a project you were doing). The chessboard came out beautifully! I've found with most woodworking projects that the maker finds the faults much more noticeable than the people looking at your work. :)
    I am commenting on this section because of the arch you cut. If you put an accessory fence on your table saw that allows adjustment for 0-90 degrees so work can pass parallel to the saw blade as well as perpendicular to it, you can use the standard saw blade as a dado to cut arches and grooves. I just thought I'd mention it because it works much better than you'd think, and it doesn't cost anything (other than building the adjustable fence, which can just be some scrap cut at an angle and clamped to the table).

  2. I have seen coves cut for molding that way - I have never done it.

    I did come up with another way based upon geometry: Draw a line between two points on a circle. Draw a line normal to that line, through its midpoint. The normal line passes through the center of the circle. If you have 3 points on the circle you can do this twice - where the normal lines intersect is the center of the circle. No math needed! You just need a ruler and a square. And in this case, long-beamed trammel points!