A scrollsaw could do it, but it might get unwieldy if it were very long. A hand-held jig saw might be a good choice, too.

I use a scrollsaw all the time and it would be my first choice. I do agree that if it is very long, it's going to flex (if it's only 1/4") so take care or have someone hold the other end while you cut. I would look at is as a series of VVVVVVV's and start at the bottom right section of the V and cut up to the top. Do all the right sides, then go back and do all the left. Don't plan to turn around where the tops meet. Hope that's clear.

Thank you both for your responses. Do you think this would work better then doing it 1/4 " thick from the start? What if I kept the length at about 3'. Then I doubled or tripled the thickness to 1/2 or 3/4 of an inch (plus the thickness of a blade). Could I then cut the scallops then rip it once or twice to get the 1/4 inch thickness. Or even possibly thicker than that.

It seems like the added thickness would give it some stability while cutting the scallops and I would get 2 to 3 times the length of finished molding. Seems like it would be easier to sand the scalloped edge if it was thicker as well.

I am not sure if you can rip something that thin or what saw you would need to do that with either. If that could be done I could probably get a carpenter friend to rip it. Do you think it would just end up breaking?

Thanks again for your imput.

I would run the stock down to final thickness before cutting the scallops. Ripping an already-scalloped piece in two with good results would require more finely tuned machinery (and luck) than most people have.

Whatever tool you choose, buy extra wood with the expectation that you will ruin some of it. Don't obsess too much over finding the perfect method, because there isn't one; just give it a try and adjust your technique as you go.

I am curious what is the total length of the piece you are planning to make and what type wood are you using? If you tried to do it as your last suggestion, you would have seam lines where it was joined. I would agree with Jon, it's better if you did it in the thickness you really want.

Sorry it took so long to get back to you. Life has a way of getting in the way of what you want to do.

What I would like to use this for is to trim a section of kitchen cabinets under a slightly built up crown and for trimming the top of the window and door casings in that room.
I have seen it done on both and it looks fantastic.

If I can figure out how it is made I would be painting it, so hopefully I would be able to hide the seams just a bit and perhaps where it wouldn't be at eye level would help some. I think I would try poplar first as it will be painted.

I just found an article in an old copy of "This Old House" where Tommy made 135 feet of greek key molding the way I mentioned. Cutting the tight curves of a scalloped molding will be a lot tricker. But there has got to be a way to do it as I have seen a number of examples of it. They also did it back in the day without all the fancy tools we have available to us today.