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Mortise and Tenon Fit Tolerances 
Question
Forum Responses
On both, I use the shoulder for alignment. I use the Brian Boggs criterion of getting a slight pop as I pull the tenon out of the dry mortise. Hammering to seat a tenon means that there is no room for glue on the faces of the joint.
From contributor B: I agree with contributor A. Also, if the tenons are too tight you might bust the receiving piece or if it doesn't bust the tenon can also spread the mortised piece creating a fat spot at the joint. When you use yellow glue the water in the glue causes wood to swell a little also. Combine glue swell with a tenon thats too tight, then sand before the moisture swell has gone. When you rub your hand across the joint a week or two later you'll have a nice dip. With the right lighting after you install this you can look at it everyday and it will say don't do that again. Im speaking from one of my personal experiences. From contributor C: If I may quote a great master It should be tight enough so it needs to be tap with a hat! Not too loose, not too tight! What really counts is having the shoulders tight, not much on the cheeks, but well balanced. 1/16 at the bottom is enough, 1/32 is too little! Its a balance, like anything else. The cheeks should NOT be larger than 1/3 of the thickness of the piece as a general rule. (ie: 1 = 5/16 tenon thickness. Ύ = Ό tenon. 1 Ό = 3/8 tenon. Always better less thick than too thick. Bigger is not always better!!
From contributor A: Our criterion is that the frames should be dry fit first, taken off the bench, then brought back on the bench for assembly. Since some of our frames are over 8' tall, it is important that the tenons be snug enough so that the top rail won't come loose and bonk anyone when stood up off the bench, but loose enough to go 95% of the way with hand pressure. Our tenons range from 3/4 x 3 x 10" in White Oak to 1/4 x 3/4 x 1 in Pine, so it is a challenge. Would you like to add information to this article? Interested in writing or submitting an article? Have a question about this article? Have you reviewed the related Knowledge Base areas below? 
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