Hi Ralph, Cutting good mitres on a table saw is very difficult. There are a lot of things to go wrong.
First is the precision of the mitre gauge. Then the fence of the gauge tends to be pretty short, 8 inches or so it is fairly easy to find the work either pulling along or pivoting just slightly when it meets the resistance of the saw. Then there is the question of the saw blade first being precisely parallel to the mitre slot and being precisely vertical. Finally, depending on the length of the stick being pushed through, are you able to hold it precisely flat to the table? Any even small error is immediately doubled when you marry the pieces together. Many of these things can also apply to a dedicated compound mitre saw but the work is fixed and there is a clamping mechanism to hold the piece down to the table and against the fence. I noticed the other day that my mitre saw is off vertical by a small amount. Not very much and certainly a couple of years ago it wouldn't have mattered but I can detect it as being off over the depth of a 3/4ths inch thick MDF board by about the thickness of a sheet of typing paper. Depending on how the pieces lay up this could represent an opening of the mitre of the thickness of a playing card, easily visible. If you close it up then the frame won't sit flat on the wall. Many wood workers use a fixed disk sander to tune up the mitre deliberately cutting it a bit long then grinding it to precise length. They will also mark each piece, never assume anything is square or that even your rabbets are precisely parallel. There are after market mitre gauges some with a triangular brace to stiffen them further. The better ones are quite expensive. They are long and therefore support work better and they have stops which can be positioned to permit you to cut several identical pieces without having to measure each one. There are also sleds. Often these run in both mitre slots and carry the work piece through the saw. Many people make their own and some even make a series of them for specific angles. Turners for example will often build a sled to cut 18 degree angles or something else so they can cut a 10 or 12 piece assembly to be glued together for turning on a lathe. Commercially available sleds can be pretty expensive and I don't see many, more often sliding tables. This can get the 45 correct particularly if the blade is correctly set up parallel to the mitre slots. Then there is the precision of the blade being vertical. I check mine from time-to-time by standing a piece of waste on edge, something about 2 and a half inches wide and setting the blade full height. I run the piece through on it's edge cutting about a foot off the end then examine what happens when I put the cut ends together but one flipped over. If the blade is absolutely at right angles to the table it shouldn't matter which way around the cut edges are approximated. You can also lay one piece on the other with cut ends facing the same way then flip one and see that the cut faces remain absolutely flush with each other. This will pick up very small imprecision, much better than anything I can detect with a square on the table and against the blade. Finally I always dry fit mitres before attempting to join them. I have a rather nice strap clamp my son got me a couple of years ago, I should buy a couple of more, I use it for all sorts of square set-up. It has a fabric webbing strap with a 90 degree corner on a threaded rod where the ends of the strap meet and lock on to. There are three other 90 degree plastic corners threaded through the strap. You position them on the corners, draw the strap tight to the fourth corner device and lock them in then tighten the lot by turning the threaded rod. Only trouble is that you cannot apply nails but if the mitres are correct the fit will be correct.If the mitre surface is adequate I will insert a size 0 biscuit and glue it up then pull it together with the strap clamp. Finally, there are mitre clamps out there. these come in different varieties. some are something like a pair of vices stuck together at a corner at 90 degrees to each other, you slide the two joining members into place with glue. Some have holes big enough to tap nails through into the frame while supported in the clamp and you set the nails while at it. Some are only half an inch high jaws or less leaving room to nail. You can also buy dedicated hand mitre saws sometimes called picture framing saws. These can be bolted to a table or cabinet and have two clamps at either side of a frame which holds a stiff backed saw. The clamps are designed to present the wood to the saw at 45 degrees from either side, the saw is suspended on posts and can then be lowered to the wood held firmly straight and vertical like using a mitre box only you don't wear out the kerfs in the box. The clamps can then be used to hold the mitre in place while you glue and nail it. I suppose you could use those so-called bow-tie connecters. This is a technique where you cut a bow-tie sort of shaped recess across the joint and cut a bow-tie shaped insert which fits tightly into the cut recess then apply glue and tap it down pulling the joint together. This was a common technique used a couple of hundred of years ago. Back then they hid the connection under the joint where it wouldn't be seen but these days anyone skilled enough to do that will usually put them right out front where they are easily seen. Hope some of this is helpful. Dale Leavens, Cochrane Ontario Canada [EMAIL PROTECTED] Skype DaleLeavens Come and meet Aurora, Nakita and Nanook at our polar bear habitat. ----- Original Message ----- From: Ralph Supernaw To: [email protected] Sent: Sunday, November 11, 2007 4:19 PM Subject: [BlindHandyMan] Bulletin Board Frame My wife bought a cheap bulletin board for church that had a cheap metal frame. I told her it would be no problem to make an attractive wood frame. That was ignorance speaking. There is nothing fancy. I want a flat frame with 45 degree beveled corners. I have a rabbit around the inside edge where the bulletin board will fit. I just tried to assemble the four pieces. Every corner has problems. I'm not sure if they are open because I didn't have the boards snug when I fastened them with a brad nailer. Or, they may not have been exactly 45 degree bevels cut in the wood. Plus the surfaces on the front aren't completely even with each other. I know part of my problem was trying to figure out how to hold the pieces in the right place so I could nail them. Any tips or tricks for this kind of project? Using a table saw, how do you get the bevels right? Ralph [Non-text portions of this message have been removed] [Non-text portions of this message have been removed]
