Shopsmith Conical Sanding Disc Review

The Conical Sanding Disc (555435) from Shopsmith is a very cool accessory that is way more than meets the eye. The standard Shopsmith 12" sanding discs works great for end grain touch-ups, but it's rather useless for edge sanding. Why?
The proper way to edge sand with a disc sander on the Mark 5 (Model 500, 505 and 510) is to offset the fence with one of the set screws in the base of the rip fence. By slightly extending the set screw which is the furthest away from the disc, the back of the fence will swing slightly away from the disc. (More on this setscrew later)

When you run a board between the fence and the disc the sandpaper you feed the board from the rear toward the front of the table. This way the disc will only contact the board as the sandpaper is heading downward. Do this wrong and the disk will lift the board or worse.
OK, that's a safe method, but the problem is this cross grain sanding will leave some tenacious scratches on the edge of the board, and on thicker boards the edge will not be square.

Enter the Shopsmith Conical Sanding Disc. The first thing that this disc requires is the main table needs to be tilted 4 degrees into the disc. That makes sense, because of the disc is tapered 4 degrees away from the table at the top, in order to get a square edge you'd have to tilt the table to match. The next difference from the method described above is that you no longer need to offset the fence. This is one of the reasons the fence on the 520 doesn't have the setscrew mentioned above. (Don't forget, there's more to come on that)

With the table tilted and the fence locked squarely in place, when the board kisses the disc it will touch the abrasive at the center of the disc; right at the point where the disc is moving perfectly parallel with the edge grain! This neat little characteristic is also what allow the conical disc to be used for sharpening jointer and planer knives.

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Oh yeah, the setscrew.
One of the most common mistakes made by folks when aligning the fence on the 500, 505 and 510 Mark V's is that they use the setscrews in the base of the fence for alignment of the fence. These setscrews (in the case of the very early 500 units: setscrew) are used only for misalignment as described above. In fact, I've experienced a few of these setscrews that have fallen out, or moved forward due to vibration, and when the fence was brought into position they threw the fence out of alignment. So, I developed the habit of removing these setscrews and I temporarily relocate them to the two threaded holes in the top of the miter gauge protractor. This way I always know where they are when I need them, plus in the miter gauge they can be used to hold a miter stop block.