I'm presenting this accessory mainly as an example of a good theory that doesn't work all that well in practice. It isn't that this doesn't work really, it does, it just isn't as useful as I thought it might be when I made it. Basically this accessory consists of a threaded rod used as a means of stopping the X-axis movement in one direction by known, uniform, and repeatable increments. The second part of the unit is actually an indicator / stop. The indexer is attached to the top of the Mortise Rail, the stop is attached to the Rat chassis and (importantly) abuts the Rat baseplate.

To use the jig, one sets the zero reference position and locks the indexer down. If for example one were using this to make box joints ½" wide, the index would be rotated back 16 times (because it is a 3/8-16 rod and the joint pitch is 1") and the Rat carriage moved to the new stop position. A line on the stop is aligned with a line on a collar near the end of the rod to ensure the rod is rotated on full increments. If you can imagine making an 8 inch wide box using this jig you can probably see the tedium involved here and the problem. Basically the threaded rod is pitched much too fine. An ACME threaded rod would be a better choice assuming of course it is even a good idea to begin with.

While I could improve upon this jig I don't plan to because I just don't think it is all that worthwhile. No matter what I do with this jig it cannot be turned into an Incra positioner or a precision instrument.