I haven't made any box joints for a few years and had a project that I wanted to use them on. I have a very nice set of 2 Freud blades that make precision cuts. I set everything up and made a cut on scrap. Then used a digital mich to see how well it did. It measured o.30 and my precision cut wasn't so precision. I removed the blades, cleaned them and recut another one with the same results. Next I checked blade squareness vs miter and blade vs table. NO help. I disassembled my miter,  readjusted to specs and tightened out any play. NO help. Then it dawned on me that I no longer have a belt drive saw, instead I now have direct drive saw. I checked the run out on the blades there was my problem Each one had the same problem due to the motor bearings having a tiny bit of play. Oh well I guess I'll set up a box joint jig to use on my router.

Sure wish I had my old huge cast iron sears belt drive. Just did't have the room for it.

Sorry to hear about the poor tolerance of the saw. I never realized there was that much difference.

Ron, what method are you using to cut them on your table saw? I use a wonderful home made jig that doesn't matter how square your blade or run out is, it's tight and accurate.

John, I never got started with my jig, but I use one like most woodworkers use. Pretty simple.  However I can't  show you a picture because I dismantled it and have been working with my router to make a Jig for it.

I would like to see yours. Can you post a picture?

Will do Ron, asap!

Ron for now though, before I get mine up here, this is what I use, very simple, this is shown on Wood Magazines Site. After you make a pass, you simply hook the new cut joint over the finger that is to the left of the blade in this image, then you make another pass, and so on till all the joints are cut.

You can see where this is going right? You don't even need instructions on how to make one, it's pretty straight forward. And you can see why the runout or play in your blade doesn't matter.

Here is their video too. In this video he is making the jig, cutting the notch for the finger to fit into, the finger is cut the same size as the box joints you want to make.
I am sorry for not posting mine here, but I'll get it up here shortly, I just wanted to get you something to chew on for now.

Hey Ron, I had a dewalt benchtop saw that I bought with a similar problem.  When the blade was slowing down you could actually see the wobble.  What i found was that the washer on the arbor between the blade and the motor was not true from side to side.  My fix, I brought the washer to a gunsmith and had him turn the washer on his lathe so it was parallel from side to side.  This fixed the runout to acceptable tolerences for a portable saw.

I have a couple of routers and I'd rather make a simple set up for one of them than mess with the table saw. 

to make box joints. I was advised not to buy direct drive saw because of the exact problem I am having. However it still makes near perfect cuts with the regular blade on it.  I'd love to have a nice, heavy table saw, but storage in my half of the garage prevents that

 the saw is now 6 years old and If I  have to replace this saw, I have a lot more knowledge now to make a better choice

Maybe a bench top belt drive would work.

What brand of saw is this?