?Great stuff ! What a rich resource you guys are.

Here are some thoughts on your excellent replies.
First, Mark T's dwg is correct for the ties. They are 1.5" thick, ~ 16 inches long and 2-1/2" high.? The material is recycled, molded plastic.?
The specs on spacing of the grooves is 7-5/8" +.092, -0.? Or, better said, 7.667 +- .046 if my math is correct.?
Jonathan M: The length of the ties are nominal, so making one cut and flipping them means you handle them twice, and any error in length is translated into an error on spacing.
Hence my desire to make both cuts in one pass.

George W; 18,500 pieces, at 3 per foot means we are refurbishing 6,175' of track with wood ties. Our RR has about 1.8 miles of track, and the older track is on wooden ties, which we are replacing.
Scale for narrow gage is 2.5"/ ft, for standard gage is 1.5"/ ft, so both can run on the same track.
The precision required is to keep the engine wheels on the track, especially on curves, and with variability introduced during th making of the track panels.
You can visit our website at pvarr.org if you want to see the operation.

The CNC machine idea is great, maybe the best, but we are a volunteer organization with a low budget, so looking for reliable, safe, low cost solutions.
We do have folks with excellent metal working capabilities, so making a dedicated machine is not a challenge.
It would be like the Woodmaster that Imram suggested. By the way, the right sized Woodmaster has? 5 hp motor.
Interesting idea to buy one used and resell.

A router table with two routers is a good idea, much easier to make than the dedicated machine.
Mark T.: On a formica (slippery) table with a fence at right angles also good idea. I was thinking of the frame idea so one team could be loading a frame, another pushing it through, third disassembling.
Good choice on the router bits.

Brian: Rebate cutters are also a good idea, because the inside dimension of the cut must be precise, but the outside cut can be a little large, so 50mm or 2" would work
David B. We are vols, so no pay, it is boring, but fun to figure out.

Thanks again.? If this inspires more ideas, I'd love to hear them.

Mike Ward