favorite method for making ply scarf joints
I am having a heck of a time making scarf joints in the 4' of plywood. I am using my radial arm saw with a sanding disc attachment. It seems that as I am sliding the ply against the backstop, it is crushing the delicate feathered edge... is there a better way? I was thinking of switching to a hand plane method but it does not seem precise enough. Attached is a pick of my radial arm saw set up.
I have never seen a radial arm saw set up that way, but I will suggest a solution to your problem.
You need a carriage that can ride against your fence and support your workpiece. Get a section of say 1/2" thick plywood and use double sided carpet tape to temporarily attach the workpiece that you are scarfing to that base plywood. The edge of the plywood rides against the fence while the part that it is carrying gets scarfed by the sanding disk. After the entire assembly is passed through the saw, peel the part off of the carriage plywood.
Now I feel obligated to offer a safety warning. Woodworkers avoid tool setups that can pinch a workpiece between a blade and a fence. Your setup matches that description. The danger is that the work gets pinched, the power tool grabs it and throws it back at high speed. As the warning labels say "Serious injury or death can result." If you have not seen a chunk of wood go flying across the shop, you can not appreciate the hazard enough. If you can find a tool that allows you to run your workpiece over the sanding disk rather than under it, you will be much less likely to have a problem that can result in injury.
The suggestion for making a carriage for your work can be used on a scarfing setup for a drum sander, a sanding disk mounted in a table saw, and router table scarfing setups.
Best of luck and be safe,
Much better with the board taking the brunt of the fence contact... Excellent points on safety, oh yes I have sent a few small missiles through the shop... I got the idea for this set up off of an EAA homebuilders dvd...
Don't make the full width scarf all at once. Try about half or 1/3 of the width at a time, taking a couple of passes to work up to the full width.
Another method to guide the ply past the sanding disc is to clamp a cleat under it which runs along the front edge of the table leaving the scarfed edge clear of the rear fence preventing the damage you're referring to. Works a treat and the cleat also prevents the ply being "sucked" more deeply under the sanding disc and binding.
I have recently built a small scarfing jig using a trim router.
I built this as a trial before building a larger version for covering the control surfaces. I was concerned about pinching of materials and chose not to use my saws for scarfing.
I have built this sanding scarfer with a disk drum. Very accurate 1 to 20+. Plywood stays fixed and scarfer moves.
This is a 18" rail version but you can use any straight steel rail and any length.