I'm working on a Taylor Baby with really high action. There is only one shim on these models under the fretboard tongue (there is no heel on these necks). The factory shim is a 16. I got various shims from Taylor after telling them my target action. They sent me 24, 26, 28 and 30. Is it ok to stack these shims? It seems to be the only way to get me where I want to be with the action. Thank you.
I've never had to, but I don't see why you couldn't stack 'em.
Sure you can stack them. If you are really OCD, you can superglue them together :-)
I can’t imagine that you woould need to stack the shims. They are designed so that one shim sits in the pocket and sets the angle. You swap them out for another one that is a bit thicker/thinner at the leading edge (they are wedges). I have done this by adding a couple of layers of masking tape to one end of the back side of a shim - because I did not have access to replacement ones of different thickness. It worked fine. But my point is that you are not trying to raise the neck out of the pocket - you are changing the angle. You should find that swapping one shim for another will change the neck angle to a significant degree.
two shims stacked together would be wildly too thick, it probably wouldn't even fit.
if the shims you have won't give you enough positive neck angle then you can cheat by adding a bit of thick paper or whatever to the body end of the pocket to add to the angle. the shim is fully supported so there's no risk of breaking anything from the pressure on the joint.
that said, it's really unlikely that you can't get there with one of the other shims if you have them going up to #30. if not, you're probably doing something wrong.
Make sure the pocket is totally clean and the surface the shim is sitting on is dead flat. It only takes a bit of sawdust or a drop of dried finish under the shim to make it sit a bit proud and put the angle off by 2 degrees, which changes everything.