RiotNrrd,
Thanks. Your explanation and excellent drawing helps a lot. Now I understand.

So the attachment to the Shopsmith base goes on once, and the outrigger goes on or comes off easily as needed. You're shaping the attachment inside/outside to match the curvy part of the Shopsmith base, so you can sandwhich it together and you're drilling thru the base to hold the sandwhich together.
riot_nrrd wrote:I showed feet in the orignal drawing, so if you want, install some adjustable feet so you can tweak it for stability.
This comment about the feet and their adjustability got me thinking about the purpose of the outrigger. The purpose is to extend the furthest-back point on the Shopsmith+outrigger's footprint about a foot backward, beneath the outfeed portion of the table, in contact with the floor, to resist toppling. The outrigger(s) will do that well and be easily removable, and the adjustable foot will take up any slack.
riot_nrrd wrote:Since it's job is not to carry the load so much as it is to keep the thing from falling over, I don't think it has to be super strong - just rigid.
So I started thinking about the outrigger bending, and how this compares with a 520 adjustable leg. The outrigger is at 0 degrees and the leg is at 90 degrees. I started thinking about something in between. The outrigger needs to resist bending (for wood, that means heft & weight) while the leg needs to resist compression (easier for wood, but since the Shopsmith leg is attached to Shopsmith table, and the table adjusts up/down, that means the leg length needs to change and then resist compression, which can also be accomplished in wood, but isn't trivial).
So, what if we had a leg at ~45 degrees, attached to the Shopsmith (not the Custom Table)? I just went down to my shop and jammed a 4' 2x4 at an angle back thru the 2 lower way tubes all the way on the right side. It touches the floor about 18" behind the Shopsmith standard footprint, so it serves the outrigger purpose of extending footprint rearward. (See attached figure) It might slide forward, rather than resisting toppling, so it would need something strong to resist that, without scratching the tubes, e.g., a 3" long 3/4" diameter removable dowel piece, fit into a 1" deep 3/4" diameter hole in the top surface of the 2x4, contacting the back of the back lower way tube. And my 4' 2x4 could be trimmed to about ~40" so it doesn't stick out in front and get in the way. The 2x4 is strongest against bending in this orientation, and takes up only 1.5" along the lower way tubes. We could put one of these on the right and another on the left as with the outriggers.
I think it might work. Not sure if the dowel is hefty enough, or if its hole in the 2x4 would weaken it too much (it's on the compressive side in bending, and only half the width of the 2x4, so that helps. Maybe a collar around the 2x4, like
those plastic 2x4 shelf-construction brackets that Lowes sells, with a 1/4" bolt/knob would be better, since it would be additive, rather than removing a lot of wood, and it would distribute the load better?
-w4f