A radial arm saw excels at truing a wavy edge on a board or panel so you can reliably use that piece again.
Step 1: Very Simple Accessories Are Required
An old piece of painted 1/4 inch plywood is resting on the table for my radial arm saw. The edge facing the camera is not quite straight, but varies almost 1/4 inch over its length.
On top of the painted plywood is a piece of 3/4 inch plywood four feet long and about six inches wide. It was cut from the end of a plywood sheet 4 x 8 feet in size. The edge facing the camera is the factory cut edge, which is very straight and true. After cutting it from a new sheet of plywood many years ago, I placed the machine cut edge against a fence and trimmed it with a rip cut so both edges are completely parallel. I have kept this piece as an important accessory in my workshop for many years. I often use it as a guide for my circular saw. Here I will show it in use as a guide for truing the wavy edge of the 1/4 inch plywood.
In addition to the plywood guide, a couple of "C" clamps and a measure are needed.
Step 2: Clamp the Guide
Turn the piece to be trued over. Place the straightedge guide on the piece to be trued. Measure in from the corner an arbitrary amount and clamp the guide to the plywood, usually about eight to ten inches. Notice that the clamp is to the right of the guide. The left (working) edge of the guide will ride against the front of the radial arm saw's table. Go to the other end of the piece to be trued and clamp the working edge of the guide at the same distance used here.
Step 3: Preparing the Saw
A couple of safety features on the saw need to be set. Turn the saw's motor for the out-rip position (blade parallel to the front of the saw table, blade side away from the saw's column and toward the front of the saw table). Turn your workpiece over again so the plywood guide is under it. Slide the workpiece and guide up to the edge of the saw table. Pull the saw motor toward the front edge of the saw table. Adjust the front of the blade guard so it is just a very little above the top surface of the work piece. Lock the blade guard in position.
Step 4: A Second Safety Feature
Lower the anti-kickback paws and lock in place so the pointed end will dig into the wood if the blade should ever catch the wood and want to throw it back at you.
Newer radial arm saws usually have a clear plastic blade guard that automatically rides over the workpiece and restricts access to the side of the blade. Some of these are two pieces of steel shaped like a "C" and laying on their sides. Retro-fit kits are available for some saws made without these blade guards, but not for my saw. It is too old.
Step 5: Set the Saw's Position on the Arm and Lock
The saw motor slides on the saw's arm. Pull it toward the front edge of the saw table until the blade will trim a minimum amount from the wavy edge. There is no point in wasting any more material than necessary.
You may notice a slight indentation on the saw table below the center of the blade. When a table is new, lower the spinning sawblade into it about 1/16 inch and pull the saw motor out toward the front of the saw table as far as you can. The tips of the teeth need to be just a tiny bit below the surface of the saw table so they cut all of the way through your work. Each time you use the saw, lower the teeth into this hollowed area, but not so much that the teeth dig into the table.
Step 6: Sawing for a True Edge
Put the work onto the table in front of the blade. In the photo that is the end of the saw table opposite the end nearest to the camera. Use some gentle pressure to keep the straightedge guide against the front edge of the saw table. At the same time, push the work into the spinning blade. You will also need to keep the workpiece down and in contact with the saw table. Do not let it ride up.
If the piece you need to true is longer than four feet, cut a wider guide, perhaps 12 inches wide, from the long side of a new sheet of plywood and use it for your straightedge guide. Your workpiece will likely also be larger. You may need some type of support, perhaps with rollers, to support the workpiece so you can handle it efficiently and safely.
When your cut is finished, you will have a true edge on your workpiece.
It would be possible to move the clamps one at a time without disturbing the placement of the straightedge guide and clamp again on the other side of the guide. Then you could turn the workpiece end for end and make a second true edge parallel to the first.
Step 7: Bonus
By setting the straightedge guide at an angle, you can use this arrangement to cut tapers without a special taper jig. Just measure inward differing amounts when clamping the guide according to how much taper you want. This could be a little tedious if you needed to make multiple identical tapers, but it works fine for one or two.