What quality does the kerf have to be? I can imagine any type of recip (sawzall, multi tool) going anything other than hogging out some material if you need a clean/machined looking slot around the post. I could see a bunch of simple shop built options with a saw to hog the bulk out and come back with a simple router plane type affair (something as simple as a 1/4" chisel kerfed into a couple pieces of ply) to clean it up after the fact.

If its just a construction kerf its one thing but if you need a presentable kerf around the post it gets fussy. I'd be leaning towards your undercut saw for the faces that it works and then a hand option for the remainder.

I'm sure you already know to clamp a wood guide to the post and then use a Fein tool

Bernie:

Unless you have hundreds of these to do, I think what I might do is to get a cheap Japanese style saw from Home Depot, or wherever you can get one.

Make two blocks, one the thickness of the distance of the groove off of the floor, and one thicker to sit opposite. Screw or bolt the blocks, countersunk, through the saw, positioned such that the blocks also serve as your depth of cut gauge. Saw while holding the block against the floor, using masking tape to mask the floor against scratches.

Taping the post where the cut goes might help to get a cleaner kerf as well.

FWIW. Good luck.
TonyF

An offset base on a trim router might work.

" A miniature plate joiner would be perfect !!"
Its seems to me that my Ryobi DBJ 50 joiner is exactly that. Am I misunderstanding your requirement?

Steve,

Yes......I fear I haven't explained it clearly enough. The tool has to fit UNDER shoe rail that is about 2-1/2" off the floor.

The suggestion of the offset trim router is a great idea. I will definitely be checking that out. It might just do the trick if I mount it on a plywood sub-base to raise the slotting cutter above floor level.

Thanks,
BH Davis

B.H. First, your website and historical building with curved entry fence are fascinating.
Yes, oops, I should have re-read your second post. It appears manual cutting is going to be the burden. A non-flexible manual jamb saw seems to be in order given 2.5" clearance. Specifically, how many cuts will be needed?

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Steve,

Thanks. I appreciate your taking note of the old business.......and now the old building as I finally sold that just over a week ago. I will miss it but once the fellow who bought my radius moulding business moved out last Sept. it was either look for a new tenant or lighten the load so to speak. I saved that building from the wrecking ball and then kept it for nearly 20 years. I don't feel too badly about passing it on to someone else to care for now. The new owner is going to make it into a house so that should be interesting to see happen.

There 7 full posts and 2 half posts up against the wall. As long as I can do most of the slotting with a power tool it won't be too bad to finish off under the shoe rails by hand. I may be making a bigger deal of of this than it actually is.

Thanks,
BH Davis