Even if your lumber has been planed for a true edge, changes over time can mean it is no longer true. I want to show a fixture for making a true edge with a table saw that is a little different from the traditional method, but leaves no marks on the lumber. My fixture is shown in the photo with this Introduction. But, in the next steps I will first show the more traditional method for getting a true edge with a table saw instead of with a joiner. The table saw is from a previous Instructable
My sled clamps the workpiece to a surface covered with sandpaper. The friction of the sandpaper's surface keeps the workpiece firmly in place during sawing.
- 1/2 inch plywood
- 2 x 2 wood (or similar)
- 3/4 inch and 1 1/2 inch stock for spacers
- 1/4 inch threaded rod
- "T" nuts
- Wing nuts
- Hex nuts
- 60 grit sandpaper
- Table saw
- Framing square
- Drill and bits
- Measuring stick or tape
Step 1: The Traditional Way
The usual way to get a true edge with a table saw means nailing or screwing a straight piece to the workpiece and using the straight piece as a guide against the saw's fence. The first few steps of this Instructable will illustrate that method, which I actually used to get a true edge on the plywood that became my sled. The downside of this traditional method is that it leaves marks, maybe even holes in a nice piece of wood. Later, those holes need to be sawed out or filled. That can waste expensive wood. See the text boxes to explain various parts of the photo.
Step 2: Details on the Traditional Method
Clamp the guide piece with the factory cut straight edge to the workpiece with an irregular edge. Check with a straightedge to be certain the factory cut guide will contact the fence, but the irregular edge on the workpiece does not.
Step 3: Attach the Guide With Screws
Attach the guide with the factory edge to the irregular workpiece. I used screws because they make a firmer attachment than merely tacking the two together with brads or wire nails. The screwheads are countersunk so they do not catch on the table during ripping. I used three screws.
Step 4: Set the Rip Fence
If you followed the link to view my home made table saw, you know that I use a framing square and the saw's miter gauge to set the rip fence. First, I adjust the miter gauge with the framing square so it is at a right angle to the blade. Then I measure the distance I want between the blade and the fence. I move the framing square to that position and gently slide the fence up to the framing square. Then I lock down the fence with "C" clamps. As long as nothing gets bumped, this process is quite accurate.
Step 5: Rip
Push the assembly into the saw's spinning blade while holding the guide firmly against the fence. The result will be a true edge on the irregular piece. Remove the screws that hold the guide with the factory edge to the irregular piece. Because my fence is quite long, I am able to true pieces of lumber a bit longer than my edge guide.
Step 6: Special Attachment
This step begins the process for making my truing sled. Start with a piece of plywood 3/8 or 1/2 inch thick. It should be four or five feet long and about 12 inches wide. It should have one true factory cut edge. If it does not, use the traditional method described in the previous steps to get a piece with a true edge. Mark the true edge, or rip the piece again so both edges are parallel and true. Glue half sheets of 60 grit sandpaper to the plywood opposite your preferred true edge. I realize some pieces I need to true could be as short as 2 feet long. In those cases, I can lay the workpiece over two of the pieces of sandpaper. Workpieces 3 feet long or longer can be laid over all three pieces of sandpaper.
Step 7: Drill for 1/4 Inch "T" Nuts
I located the centers for three holes and drilled a small pilot hole for each through the entire thickness of the plywood. The holes are a little over 6 inches from the edge with the sandpaper. Countersink the flange side so they do not interfere with the smooth plywood surface when the sled is sliding over the saw table. Drill 5/16 inch holes for three "T" nuts. Drive the "T" nuts fully into their countersink holes.
Step 8: Threaded Rod
Cut threaded rod. Round the ends. Use a washer and a nut above the "T" nuts to lock the threaded rod in place.
Step 9: Make Hold Down Clamps and Use
Make hold down clamps 10 inches long from something fairly sturdy. Drill holes in the hold down clamps. Use wing nuts and washers to attach the hold downs. Make 3/4 inch and 1 1/2 inch spacer blocks for lumber of both thicknesses.
The photo shows a piece of lumber 1 1/2 inches thick with spacers of the same size.
Place the lumber with an irregular edge on the sandpaper portion of the special fixture. Clamp it down to the special fixture. Grasp the workpiece and try to pull it away from the sled. If the workpiece is firmly attached, set the rip fence for the required distance from the blade. Rip the untrue edge from the irregular piece using the sled.
Step 10: The Results
The photo shows the new straight edge on the workpiece. Also on the saw table is the irregular piece trimmed away.
Remove the workpiece from the sled and put it away. Invert the workpiece. Adjust the distance between the blade and the rip fence. Rip the other edge so it is true, too.
This sled wastes less good wood than the traditional method that involves tacking or screwing the workpiece to a straightedge guide.