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Yup, your drawing is scaled down, that's what the square is for. Scale everything up by a factor of 1/0.85 or 117.6%. If you're still not sure take a look at the instructions and find two pieces that fit together (one with a hole, one with a nub) and do a test cut with those. Also, souriceaux06 made a remix with different engines that you can cut instead of the dowels like I used (dowels are much more work)