|Project by JonasB||posted 01-08-2016 07:51 PM||686 views||0 times favorited||1 comment|
I needed to cut some plywood to cover some stairs after I took out an old rug. Since nothing is really square, I used a jig that captures the shape of the tread for cutting. I think I read that shipbuilders used something similar in the old days since odd shapes are the norm in their environment.
The jig is simple. It is a thin piece of plywood that is stiff enough to hold it’s shape. It needs to be smaller that what you are measuring. For the stairs, I cut the front edge, so it aligned with the front of the stair. The top of the jig has double sided tape along the edges. The last component is a set of markers. I made mine long triangles, but any shape can be used. The number needed is determined by the complexity of the shape you are measuring.
In use, I placed the plywood loosely centered on the stair, and aligned it with the front edge. I then tacked on the markers to the double edged tape so that they would align with the vertical sides and riser. I then lifted the board away, flipped it over and used it to mark the board I was cutting. I used a straight edge held against the markers to improve my accuracy. The tape stayed sticky for the 9 stairs I was dealing with, but worst case, it is easy to reapply if the markers aren’t holding anymore.
Variations that are possible with this jig:
Instead of just marking 3 sides, I could have used more markers and measured all 4 sides without an alignment edge.
Any shape can be measured not just a rectangle, you just need a board smaller then the space being measured and enough markers to capture the desired details.
If the walls are tapered and you can’t get the board out after the markers are in place, you can draw the outline of one set of markers on the jig board and then tape them down using the sketched in lines after you extract the jig.
Instead of the way, I used a straight edge to mark the cut line, you can just outline the markers on your target board, remove the jig and then draw your cut lines using the outlines. My thought was that using the straight edge recreated the walls very accurately and I only had to deal with the variability of one pencil line rather then two. I did encounter one riser that bulged in the middle, so could not use the straightedge and had to create a curve.