I've been getting questions about how I did my center ankle. I used rails like these to hold them on but that's later...
I can try explaining mine but I'm kinda bad at it. I went off of Victor
Franco's method (Mike Senna's plans/blueprints). Basically make a wooden
leg (3 layers of 1/2 wood ) only like 12-14 inches tall and not the top
part of the leg. Your center ankle should look like this...

this is Victor's
never mind the center caster holder. Ask Victor Franco how he did his
because I didn't follow his method. I took 2 thick pieces of wood and
glued them together and then bolted the wheels on...this is victor's...
http://farm1.static.flickr.com/213/4...f35d63.jpg?v=0
If you haven't made wood legs before here are the plans (leg assembly or
leg outer? Don't remember which one). Also look at this for a tutorial
on how to make the legs
http://pw2.netcom.com/~artoodetoo/LegTutorial.pdf
. Do this but only make the bottom half of the leg. Ask in the threads
for the official blueprints because I haven't found them

.
Victor lent me his MDF leg to trace. ZHunter sold me full sized
blueprints so maybe he can point you to the official blueprints.
For putting the ankle in the body you need rails like these...they need
to be strong but also the right length (around 5-6 inches long depending
on how long that metal plate in the com frame is and if you can drill
holes in it)....
with a hole at each end so they can be bolted onto the frame and 2 on
each other side so longer bolts can go through the center ankle and hold
it there. This is mine...if you notice how the rail and bolts are on
mine...
Pictures are all squished again
:(
I got the rails from Mike Senna
Hope this helps a bit. I only know Senna wood frame so I'm not sure how
this would translate to others. Others might have to shorten the center ankle to have
it not hit anything in other frmaes. Victor does this better and I based
mine on his. I'm still kind of a newbie and had to let Roy Powers and
Victor put my center ankle in

.
PM Victor Franco about this for more detail because I just kinda bought bolts
and such and watched. Didn't trust myself with a drill press yet. Sorry
if this is confusing or a bad explanation.