While I had been thinking about how to make the arms from the time I had started scheming to build this chair, by the time I got to this point, I still hadn't worked out a firm plan of attack.

The original's arms are clearly made from a single piece of thick stock.   With my 5/4 stock, I would need to glue-up something. 

I did think about steam bending thin pieces and using a form.  But I would need to build a steam box, and sometimes spring-back can be an issue with this method.   So, I did not explore steam bending.

Being impatient to get moving in some direction, I glued-up a couple pieces of stock and figured I'd somehow work out how to shape the curve using a combination of bandsaw cuts and router template shaping.

While I would have liked to keep the appearance of a single piece of wood on the top surface of the arm, I was increasingly uneasy about trying to use template routing on a 3.5" tall surface (with the arm on its side).  I had even built a Rube Goldberg style jig to align a router templates on either side of the arm so that 1/2 of the arm's width could be cut from each side.  I ultimately abandoned this approach before even using the jig.

Instead, I decided to cut out two curved pieces from face of the blank, and glue them together to form the arm.  This meant there would be distinct individual pieces visible on the top of the arm, but I was prepared to accept that for a safer build.  Still, the arm blank was about 2" thick, which is still pretty high for template routing something so narrow.   I made a router template with built-in stabilizers at each end to help keep the work vertical while it was being shaped.  This worked pretty well.

I left the two pieces long just in case there was some slippage during glue-up.  I'll cut to final length afterwards.

Before working on the remaining arms, I turned my attention to the finger joints and how to clamp the curved arms in the Leigh jig.  I added a moveable fence that would be used to index the side of the arm rather than using the tiny fence that's built-in to the jig.  With the long fence perfectly square, I'll be able to clamp in the arm and go.

The fence is longer than the arm so that a block can be clamped near the end to index
the lower end of the arm.  This will ensure that the curved arm is perfectly vertical when clamped in place.

I confirmed that the fence position centers the work to match the fingers of the leg.

With the arm set in place, it still requires something to clamp against - I used the same wedge I used on the legs. 

With everything looking good, I cut the fingers on both ends of the arm.  This took no time at all with the new fence setup.  One arm down, three to go.

For the next arm, I decided to try just cutting out 4 individual pieces from the stock.   This time, I cut the pieces to final width and used a regular router template for the curve.

This worked out great.  Very little variation between the pieces - certainly no big deal to sand out later.

Once glued together (and keeping the cut ends aligned was not a problem), I dressed the joint surface with a card scraper just to even it out before cutting the fingers.

This worked well enough that I used the same process for the remaining two arm glue-ups. 

Once all three were glued-up, I cut them all to final width on the table saw.

And finally, made quick work of cutting the fingers.