I'm building some shaker style doors out of maple and want to incorporate a visible pin in the rail/stile mortise and tenon joints. How should the grain be oriented for the pins (with the rail or stile)?
Use end grain pins.
You will want to use a pin so that the end grain will be exposed. Beyond that, there would be the slightest advantage to making the grain run the same direction as the rails. It will be more difficult to crush the fibers lengthwise. We may be splitting hairs here, though. I am sure that there are many surviving doors that have pin grains running all directions.
The draw bore would be unneeded with the good glue today, but the principle of the operation dictates a long grain pin in every case. To do otherwise screams that the maker did not know or understand his work and the reasoning behind it.
Worse even than those awful decorative dovetails routed into anything to show craft. Nakashima excepted due to function, of course.
For the sake of argument, if I were to use a face grain plug intended to mimic a true pin, which ultimately made the job profitable and the customer happy, would "the maker" still not understand his work and the reasoning behind it?
Further, is it implausible to think that pins could be turned with the face grain showing (a daunting task no doubt) and inserted into the joint with glue only on the facing portion of the stile limiting the pin's movement to the back side (unseen) part of the door? With the grain oriented with the stile, in this case, there would be no visible compression set, and so long as the mortise and tenon joint was sound, the joint would be just as long lived.
One thing is certain. There is always another way to do it. Nakashima based his entire style on that fact.
It is fair to say that Nakashima's exposed joinery is functional, not applied. If you have a client who is willing to pay for decorative overlays on a concealed joint, have at it. One thing to consider is surface treatment. Flush looks good if well done. Domed or pyramid pin ends add depth and texture and the reveal may hide minor inaccuracies in cutting the mortise.