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Getting ready to glue head and tail blocks into a 000, shooting for 4.5 in final depth at tail, 3 5/8 in depth at head block. My question - how do you all get the depth to a predetermined, predictable measurement? In my past builds, I haven't cared too much, I'd start with a tail block of, say 4 5/8, and it ended up where it ended up after the sanding dish. Trying to be more refined than that.

I'm using 28 ft top, 15 ft back radius. My thought is to leave the sides 1/4 inch proud or so, and sand down til the blocks are radiused. Any other ideas? You'd think I would have measured the before and after conditions in one of my builds, but nooooo....

I love how every build gets slightly better and more precise. Best lifetime hobby ever.

Tom, I subtract the thickness of my top and back, then work the rim until it matches.

I also take measurements on each side of the shoulders and lower bout to make sure things are staying square.

Exactly. Mark the sides so you can see that one side isn't getting thinner than the other. Is your lining in yet? If not, leave yourself a little wiggle room for getting it flush. I also don't think you need to leave 1/4" to spare, unless you're trying to buff up...

"unless you're trying to buff up"

Not such a bad idea!

I first put the completed rib assembly, top down, on my 25 foot radius dish, shim it to level, and use a half pencil on a block, following the top radius dish, marking the ribs all the way around, Then trim with a block plane just short of the line and sand in the radius dish, using chalk to see where I have not sanded.
I then mark the neck block and tail areas with the depth (allowing for the top and back thicknesses) and place the rib assembly back down in the back radius dish.
Shim again, getting the mark at the neck and tail ends the same distance above the radius dish, and the ribs level at the top edge of the lower bout (at widest point) unless I want a wedged body.
Then get another block/shim which matches the height of the marks at neck and tail ends, draw all the way around, trim with block plane just outside the line, and then sand on back radius dish just on the line.
Then I fit the kerfed liners, slightly proud, trim with block plane and sand back again.
Hope that makes sense.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.