Q: I bought one of those long metal straightedges used to guide a circular saw when making long cuts. But the cuts I made with it aren't quite straight. Is there any way I can check the straightedge to see if it's okay? I'm not sure if my bad cuts are my fault or that of the straightedge. A: There's a very simple trick you can use to check that saw guide. Stick a pair of pushpins or small brads into a long board or sheet of plywood. Space them a little less than the length of the sawguide apart. Place one edge of the guide against the two pins and draw a line along that edge. Then slip the guide over, push the same edge against the other side of the pins and draw another line. If the guide is straight the two lines should be parallel and a pin thickness apart. If the distances between the lines varies, the guide is not straight. Note: Some guides have a top and bottom. If you flip one of these over to draw the second line, it's edge will be raised off the work surface and won't be able to draw the second line accurately. In that case, don't flip the guide to draw the second line. Instead, swing it end for end, but make sure to move it to the other side of the pins. Q: Can you tell me where to get instructions for mounting a bed on a hinge that will swing up into a closet or against a wall? Also, what supplies will I need, and where might they be purchased? A: You are talking about the old Murphy bed, a good idea and a staple of slapstick humor many years back. I have one in my home I made from scratch using an iron pipe as a pivot and a large concrete counterweight to take some of the effort out of raising the bed. But the simplest way to get one is to write to the source: Murphy Door Bed Co., 40 East 34th Street, New York 10016. Murphy still makes foldup bed frames using springs instead of counterweights to ease operation.