Box joints

[D._Frederick]

I am making some trays for christmas presents that have rims jointed with box joints. I used a shop made jig to make the box joints on my table saw, but they turned out too tight.

Should I sand, file, rasp or etc. to make the joint less tight? I tried using the table saw but end up removing to much material.

What method would you use?

[kylerayk]

Did you cut both mating pieces at the same time or each one separately?  I have had the best luck cutting both at the same time keeping the pieces in the same relationship as they will be when assembled.  If the joint is too loose or too tight, you need to adjust the width between your dado blade and the key.  Also, when assembling I always use Titebond Extend wood glue.  It has a longer open time that allows you to do a better clamping job.

[Brad_bb]

I'd say just experiment.  Depending on how tight they are.  A file maybe, or coarse sandpaper on a flat piece of wood.  Just a couple months ago I made my first box joint jib.  It's a sled for the table saw where I cut a 1/2inch slot in the sled(for 1/2 inch joints), then on the rear upright of the sled, I marked a 1/2 inch slot, 1/2 inch over from the existing slot.  This new slot is only in the back portion and not the baseplate of the sled.  It's for installing a 1/2 inch wooden key to index your finger cuts.  I found the first time I did this that the joint was too tight, so I had to use a sharp chisel to cut a little more from one side of the slot to move the key over a bit.  Then I had to fill the side with the gap with some wood.  Once happy with the fit of the test joints, I glued the key and shim in permanently.  Once you have it set up they way you want, it should remain good.  It's all about tweaking the position of the key, and perhaps the width of the key, depending one how yours came out.  Come to think of it, I think I may have made a second key after the first was slightly too narrow.

[metalspinner]

You might spend more time fiddling with the fit of your first try than if you just started over.  I fall into that trap sometimes, too. :-\  The beauty of the jig is that you will have a perfect joint.  Trying to file or sand the fingers will give you some irregularity.  Of course, many a fine dovetail has been cut through the years with hand tools.

That being said, maybe another pass through the saw on all the joints will "adjust" the fit a little. If the wood has shrunk or expanded just a hair, the saw might just shave it enough for a good fit.  Or, set it aside for a couple of days and maybe the wood would have moved enough to go together???

Edit:
Another idea came to me this morning.  A trick chairmakers use to get super tight tenon joints is to heat the tenon in a can of hot sand.  This shrinks the tenon and provides easy assembly.  Then the tenon swells a bit in the chair providing a snug fit.    Not sure how that technique would work on the multiple fingers of a box joint, though.

[kylerayk]

My home made box joint jig has the key mounted in a separate fence that is held to my miter gauge with a couple of screws in slots.  To fine tune the fit, simply loosen the screws and move the fence and key closer or farther away from your dado head.

I have found that consistency in technique is crucial to a good fit.  I also cut my slots a bout 0.015" deeper than the stock thickness.  This causes the pins to be a bit proud of the box sides so you can sand them perfectly flush.

I built a sweet quarter sawn red oak urn for my "chain saw Uncle's" (see my post in the chainsaw forum) ashes.  I cut the pieces sequentially from the same board so the grain pattern wraps around the box.

Made another one at the same time for me when I depart this earth.  Nothin' better than being buried in your handiwork.

[Brad_bb]

If you can post a pic of your jig, I'd like to see it. Thanks