I made a bunch of drawer fronts in a shaker style and had a lot of problems getting making a consistent thickness tongues.
I first jointed and planed all stock to equal thickness. After cutting to size, I cut the tongues with a dado stack using my Incra 5000 sled. Each piece ran across the dado twice, flipping to ensure centered tongues. I had carefully set the depth and width of the dado cut on a few pieces of scrap.
I cut the grooves using a 1/8" dado blade on the table saw, running the stock through once then flipping it to ensure centered cut.
After all of this, the tongue thickness seems to be all over the place. Some are too tight, others too lose. The tight ones are easy to fix with sanding blocks, the loose ones are kind of a problem. I am curious what could be causing the discrepancy. I made sure everything was locked down and align during each cut, yet the inconsistent thickness proves something went wrong.