Ok, with my estimation I came up with a whopping total of 86 ebony plugs (with the possibility that there may be 2 additional ebony plugs below the bottom side stretchers to give us a total of 88 plugs - however, I will ignore that possibility for this chair!)
There are 8 ebony plugs that hide the 8 screws that attach the 4 bracket details to the bottom of the seat rails. Given that only babies and drunks would see those, I will simply use round mahogany plugs down there. So that brings the total down to 78. There are 2 ebony plugs on the back seat posts that hide the 2 screws that attach to the arms. Those were installed earlier.
That leaves 76 plugs to be installed!
There are a couple ways to make and install ebony plugs. I will not go into the various possibilities. To make my life much easier I purchased a couple Lee Valley square hole punches - 3/16, 1/4, and 5/16. These cover all the sizes except for 4 1/8 inch plugs on the front seat legs. For those I simply used a small drill bit and chisel. These small plugs give the appearance of securing the seat bracket details under the seat rails to the front legs.
To make the plugs I used a bandsaw and my Jet 10-20 drum sander to dimension the ebony into 3/16, 1/4 and 5/16 inch strips - although oversized about 10/1000" in both dimensions as recommended by various woodworkers out there.
Darrell Peart uses a disc sander to quickly round over the tips of the ebony strips to give it a pillow effect. Since I do not have a disc sander, I used William Ng's method of using a cordless drill and some cushioned sandpaper stations - really saves the wrists in attempting to establish the pillow effect. You can see him in action on youtube where he explains the process in more detail:
http://www.youtube.com/watch?v=HLopA6NF7dk&feature=related
Note that I had to borrow a neighbors cordless drill with a 1/2 inch chuck to handle the 5/16" ebony strips. My cordless drill has a dainty 3/8" chuck.
Now, the course grit worked great, but I had problems in totally removing the course streaks with the finer grit using the cordless drill - especially for the 5/16" sized plugs. Consequently, after establishing the pillow with the cordless drill and the course sandpaper (150 grit), I used my hand with a pendulum motion to remove the 150 grit marks using 320 and 600 grit sandpaper (not cushioned). This went pretty fast. I then took the plug to a buffing wheel to get the sweet polish. I then cut the plug to about 3/16 - 1/4 " long. Some of the plugs on the thin crest rail were a very light 3/16".
For the 2 side stretchers I had drilled a 3/16" hole and installed a round maple tenon from below to secure the center stretcher in the early stages of building this chair. I now covered the top with a 3/16" ebony plug:
Now, on the original this may be a real ebony tenon - or there may be ebony plugs above and below to hide the real hidden tenon. Not sure - and probably not too important in the big scheme of things.
Here is the very nice Lee Valley square hole punch in action:
Some of my plugs are a bit heavy, such as the one above. At least they got personality!
Probably the most challenging exercise here is with clamping and getting the chair in a position to make pounding with the square hole cutters possible (without demolishing the chair!). I had to be very careful when installing the plugs on the rather thin crest rail - using light taps. This added to the time involved in installing all these plugs. Installing 78 plugs took some time!
I also made templates:
After installing all those ebony plugs with a shiny buffed surface, the ebony splines looked very dull in comparison. I decided they needed buffing as well. I used my dremel with a buffing wheel and some buffing compound. Boy did this make a difference!
Before installing the seat cleats I consulted a professional upholsterer on how to do this. I will be using a drop-in sprung seat. He gave me the dimensions of the cleats and the recommended clearances from the top. The cleats are white oak and are 3/4" wide and are 1-5/8" from the top of the seat rail. They are both glued and screwed on for strength. I will provide him with a quality piece of 5/8" multiply birch plywood. I will have about a 1/4" clearance on all sides of the plywood for the fabric. Here is a picture of the cleats installed:
Note the corner glue blocks for added strength
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