Box Joints

[Acelectric]

I am in the process of making a box joint jig. The fingers fit together VERY tightly. My question is how tight should they be? My fingers are measuring .499 and my slots are almost exactly .500. Any advice is appreciated.

 

[Joe Scharle]

Well, I'm confused! .499 is almost .500...And should result in a good fit, since the finger is smaller than the slot. An old rule of thumb for both box joints and dovetails is "press on / tap off".
To change the finger width, move the alignment (peg/key) (closer/farther) to the blade.

 

[Acelectric]

They do go together, but only with some persuasion from a dead blow hammer. I'll more the pin a little closer to the blade and see how that works.

Thanks

 

[Bas]

.499 is very tight. I suggest you cut a few test pieces, apply some glue, and see if they come together with very slight mallet persuasion.

If you have to hit it hard....it's too tight.

If you have to pound it full force to beat into submission while sweating and cursing loudly because the glue is setting and it's JUST....TOO....TIGHT.....it's too tight.

Some species compress more easily than others, so factor that in as well. Don't test fit with pine if the final project is hickory.

 

[Acelectric]

I'm using red oak for my test pieces. After some more fine tuning I can now put them together without hitting them with a hammer but they are still tight. I'll try it with some glue on it and see if they still go together.

 

[Jeremy Scuteri]

Are you measuring the fingers and slots before you have fit them together? I am wondering if the 0.499 measurement is after the fibers have compressed.

 

[Jeff]

I'm using red oak for my test pieces. After some more fine tuning I can now put them together without hitting them with a hammer but they are still tight. I'll try it with some glue on it and see if they still go together.

The glue should act as a "lubricant" of sorts, but if those joints are still so tight then they may become glue starved when you seat them. Kind of like rubbing 2 hands together while both are clamped in a vise. Red oak is porous so it may be more forgiving in your test, but what species of wood is your final project?

 

[Acelectric]

I think I've got it adjusted pretty good now. The joints go together with just hand pressure. As soon as I find my ratchet strap I'm gonna glue up a simple box and see how it goes.

 

[tryingtokeepmyfingers]

I would say that this is where the Ibox from Incra excels since it is easy to fine tune the fit with the adjuster and why I deemed it was worth the money up front to save me time and materials down the road

glad you got your jig adjusted better and hope the glue up goes smoothly

 

[Matt Furjanic]

They do not need to be nearly that tight. They should go together easily without forcing. When glued, the joints will swell and make a solid bond. If they need forcing when dry, just wait till you apply the glue! You will be lucky to get them together at all. Here's a tip when the joints are real tight: use white Elmer's glue-all. It is pretty slippery before it dries, unlike yellow glue which grabs immediately...

 

[Acelectric]

I glued the simple little box together. It was pretty tight after applying the glue but it went together fairly well. I will probably make another adjustment to it before using it again.

 

[Joe Scharle]

I glued the simple little box together. It was pretty tight after applying the glue but it went together fairly well. I will probably make another adjustment to it before using it again.

Good!...Never hesitate on experimenting and learning. When you learn the pin to blade relationship on your box jig, it will translate to all of your joint making. I make notes on my adjustable jigs which I'll use again right on the jig itself where I can see them with the jig mounted!
Things like the micrometer reading for nearest blade tip to pin, reminders like FATTER PINS = MOVE KEY AWAY etc.

 

[Acelectric]

Here are some pics of the completed jig and a sample box made from scraps:

View image in gallery

View image in gallery

View image in gallery​

 

[Joe Scharle]

You can't buy 'em better than that :thumbs_up

Like your jig too!

 

[tryingtokeepmyfingers]

nice looking jig the photos helped

 

[Jeff]

That looks pretty good even with my tunnel vision. Ha! Nicely done.

 

[Alan in Little Washington]

Great results!

Here is something to remember if you make another jig, additional jigs for different sizes of box joints, or if you are setting an adjustable jig like the I-BOX- Theoretically if you accurately and precise make and set a box joint jig, you will get a "perfect" joint that will likely be too tight. The tight fit results from a number of factors not least of which include compression and expansion of the wood during and after the cut and the fact that no allowance is made for glue. For a nice fitting joint you may actually need to de-tune the jig slightly- reduce the spacing between the blade and the index pin by a few thousandths* of an inch. * the difference between a joint that is too loose or too tight is less than 10 thousandths of an inch!

If you really get into box making, you'll want a number of jigs, or you may want to consider buying precision, adjustable I-BOX from INCRA. Its a pretty darn good jig, if I do say so myself. The guy that invented it is a good friend!