Originally Posted by Mojotron
Of course, you are looking for a production solution. But, all I do is use a piece of a counter top remnant with sandpaper glued to it and a B/D workmate to hold the wood:
First I cut the edge of the wood to be joined on my table saw making sure that it is aligned very well. Then I sand the edges with the stone with 80-150 grit sand paper glued to it until all of the scratches are gone.
This makes as invisible of a glue line as I have seen, takes about 5 -20 minutes (depending how good your saw/alignment and cut is). It just works for what I've needed to do to join guitar bodies and it's extremely simple.
I use a joiner for rough work .
I use a granite surface plate with adhesive backed sandpaper on it similar to this in basis .
I use this process for prepping the mating surfaces of acoustic tops and backs .
You could find a junk joiner and use the table surface as a sanding surface and the fence as a guide if so inclined .
If using the sandpaper/flat surface method , I suggest prepping both pieces at the same time .