Larry Haun from Coos Bay, Oregon, writes:
This homemade device is one of those gadgets that makes me wonder “Why didn’t I think of that?” Designed by Andrew Kerley, the tool is a triangle made of 1/4-in. plywood. As shown in the video, the body of the guide is a right triangle with truncated tips. The length of the triangle’s legs is equal to the length of the block you want to cut, minus 1-1/2 in. As shown in the video, the 1-1/2 in. takes into account the distance from the base of a typical worm-drive saw to its blade. The guide shown here is designed to cut blocks that are 14-1/2 in. long in one position. Flip it over, and it guides the saw through a 13-in. block. You can modify the dimensions to cut blocks of any length and to accommodate the different blade offset of a sidewinder saw.
Note that the fences each have a hook on one end. To use the guide, lay it on the material to be cut, and snug the hook to the end of the stock. Run the saw along the guide, and repeat as necessary. If you need to take a little off the length of the block, put a thumbtack on the hook.