The depth of the dovetail cuts equals the thickness of the board the cut is being made on, and the pin and tail boards are the same thickness. Therefore if your tail & pin boards are 3/4″ thick, then the depth of the dovetail cuts will be 3/4″. The Sketch below shows the depth of cut for the tails ( T ) on the tail board & marked by the lines noted in the Sketch (“these two lines drawn using the jig show in the photo below”). The pins ( P ) represent wood to be removed, on the tail board shown in this Sketch. The lines showing the depth of cut, need to be drawn on all four sides of the board.
The Photo below shows the jig I use for marking the depth of cut for the sawn cut dovetails.
The Sketch below shows the dimensions that I used for the dovetail depth marking jig, pictured in the Photo above. Note the 3/4″ dimension shown on the smallest rectangle, this 3/4″ dimension equals the req’d depth of cut for your dovetails. If the thickness of your dovetail boards was 1/2″, then the depth of cut for your dovetails would be 1/2″, and the 3/4″ dimension shown on the smallest rectangle in the Sketch below would need to be 1/2″ (and not 3/4″).
In closing, I like to use a 0.7mm mechanical pencil to mark the four sides of my dovetail board. After sawing my tails and pins, I use a combination square & marking knife to mark the depth of the cut lines. The pencil line is easier to see when sawing, and the knife line is ideal as a micro groove to place my chisel on for removing waste between tails (on tail boards) & between pins (on pin boards).
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Until Next Time, Take Care