Posted: 8/2/2005 7:40:32 PM EDT
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I am in the process of making a Murphy bed. I need help making even square cuts over a very long piece of plywood. The cuts are up to 82" long. I am using a circular saw. Normally when I do small wood work I use a T-square clamped down as my guide. But I am making extremely long cuts and the cutting is perfect for the first 20 inches or so then by the other end of the cut something has gone wrong (like a loss of 2/8"). Even though I thought everything was square. The cut always wonders off the line. I have been using a straight piece of wood but I feel I need something better. I need a straight edge that will extend the whole length of the wood. I need some advice on how to cut perfect lines over a long distance. And making sure everything is square. |
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There are clamps which you can buy to create the straightedge you need. I just don't know if they are vailable in the length you need. I'll see if I can find a link. ETA: Here you go (example)... You may also want to consider a pipe clamp, which can be made to almost any length. I just don't know how well an 82-inch pipse will remain straight... Another option is to create a "table saw" of sorts by buying a quality piece of flat, thick plywood, mounting the circular saw to it with the blade extending throug a slot in it, then flipping the plywood over. Use one of the clamps above to create a fence, mount the plywood to some sawhorses, then run your stock through SLOWLY. Instant table saw..... 
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www.woodcraft.com/family.aspx?familyid=4607 or take it to lowes or home depot and see if they will cut it for you,using that big panel saw they have. |
| You can make a guide...often called a "shoot board"...from a really straight 1X4, etc...or I have seen guys use clamps and a metal stud to do the same thing (Lowes will have metal studs...they are cheap and straight). Actually, the easiest thing to do if you don't have many cuts is to buy the ply at Lowes or HD, mark your cuts like you need them (make a list and take it with you) and have them do it on the panel saw like hanau said, IIRC they will give you two free cuts and the rest are like 25 cents each. |
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A straight-edge clamped then use the circular saw is the way to go. I have a table saw, but for long cuts like that, I use the circular saw and straight-edge. The new edge of the new piece of plywood should be straight enough. Cut a wide enough strip off of that and clamp it to the plywood. Place the circular saw against the new edge. You could maybe sand that edge a little so the saw will slide easily along it. Just don't sand it so much that it becomes wavy. A murphy bed is quite an ambitious project for someone without a table saw. I wish you luck. If it comes out well (and the fact that you are asking these questions makes me think that you take enough pride in your work to make sure that it does), you will have some serious braggin rights. "Yep, nothin' but hand tools and my trusty old circular saw..." -RJ |
Hey! Those are new! 
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This is what I do - a steel stud or a piece of aluminum angle and a couple of inexpensive clamps and you are set. |
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Not sure if this is the issue or not, and please forgive me if I am saying something that you already recognize as obvious. Dimensional lumber (2x) often can be perfectly straight till you cut it, but end up warped and twisted as all afterwards. I have noticed the quality of (affordable) lumber decline a lot since I started doing wood work. Mills are trying to get every last board out , and now marketing boards cut too near the heart of the tree. The grain of these all but prevents ripping. The grain is too circular, and when ripped you will get some terrible warping. I suspect if you want strait cuts you will to make a jig and practically need to re-mill the boards after you rip them. Not sure if it is cost prohibitive, but life can often be much happier if you find a decent lumber yard (rather than a home improvement center), get higher quality lumber to start with. Finding a good trip shop (mill) can also be nice. Anyway, good luck with your project. Oh, treat yourself to good staight edges and clamps. If you are going to be making a ton of simular cuts, consider builing a jig. |
Somebody else mentioned having a sharp saw blade. This is every bit as important as having a ripping guide. They are inexpensive at the home improvement stores. |
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2 options I have used. 1. a factory edge (such as a sheet of plywood) from a piece of matwerial a few inches wide, clamped to your material, then use a circular saw. 2. chalk line. Follow the line and go slowly. It will be perfectly straight, but you will probably have to sand to clean it up. |
I have an extruded aluminum edge guide similar to that. It uses small C-clamps. It's invaluable IMHO. |