Box / finger joints

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Forum topic by ajthomas5009 posted 03-30-2014 12:37 AM 1265 views 0 times favorited 7 replies Add to Favorites Watch
View ajthomas5009's profile


296 posts in 2700 days

03-30-2014 12:37 AM

I was getting ready to build a few things with finger joints and had some questions. I am using a dado stack and a simple shop made jig. The past couple of days I’ve been just practicing. It seems like things came out well for being my first try at finger joints but they just seem a little too tight. To get the joints to fit properly I had to smack the hell out of them with a mallet a cpl of time. There was no damage to the fingers but it seemed about as tight as possible before damage occurred.

This didn’t seem right to me and that it would only lead to a glue starved joint. I’ve tried to research it myself but I’m getting mixed information. Some people say this type of super tight box joint is good and don’t even use glue when you get them like this. Others say is should only be tight enough to require a few light taps.

So how should box joints properly fit?

Also I can just fix a overly snug box joint by just adding a .005 shim to my dado stack right?

-- Sometimes you're flush and sometimes you're bust, and when you're up, it's never as good as it seems, and when you're down, you never think you'll be up again, but life goes on.

7 replies so far

View AandCstyle's profile


3296 posts in 3340 days

#1 posted 03-30-2014 12:50 AM

Some of the answer depends on the species of wood you are using and the width of the fingers. A soft wood and wide fingers can be forced together and no glue will be required. A hard wood will probably not be forced and a really hard wood might shatter if you try to force it. I would try a 0.002 shim first and move toward thicker if needed. Think of it like a mortise and tenon, you want the fit to require hand force, but not to require a mallet. HTH

-- Art

View gfadvm's profile


14940 posts in 3773 days

#2 posted 03-30-2014 01:10 AM

I would move the jig pin 1/10 of a skosh closer to the dado stack rather than shimming the stack. When I get those really tight box joints, I drill from the top and bottom and pin them with a 1/8” dowel rather than gluing them.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View Monte Pittman's profile

Monte Pittman

30615 posts in 3421 days

#3 posted 03-30-2014 01:22 AM

I use the Incra IBox. Works awesome. As far as adding a shim, you still want to remeasure your setup. A small mistake on box joints gets badly magnified.

-- Nature created it, I just assemble it.

View ajthomas5009's profile


296 posts in 2700 days

#4 posted 03-30-2014 01:53 AM

Ok AandCstyle your response was pretty much what I was thinking. So a few mins ago I took some of the scraps I cut and re cut them in the same jig with a .005 shim added to the dado. This time the joints came out what I’d consider a hair too loose. They would have probably have glued up fine and all but the slid together easily and a few had a little light showing through when assembled.

I know you suggested a .002 shim. I went with a .005 because it’s the smallest that came with my stack. Does anyone know of anything that’s a mil or 2 thick I could use as a shim without buying a set of shims?

-- Sometimes you're flush and sometimes you're bust, and when you're up, it's never as good as it seems, and when you're down, you never think you'll be up again, but life goes on.

View Paul's profile


721 posts in 2648 days

#5 posted 03-30-2014 02:11 AM

For single use a piece of loose leaf paper or 2 works in a pinch. cut to 2” by 2”


View The Box Whisperer's profile

The Box Whisperer

678 posts in 3153 days

#6 posted 03-30-2014 02:30 AM

box joints are my go to joint for boxes, and while I dont use a box joint jig, I use an original incra, I will still throw my 2 cents in. Back when I got the incra, in the DVD, the guy said, “a perfect box joint doesn’t need a mallet to go in and doesn’t need glue to stay in”. Ive always gone by this and its worked for me. I use regular PA wood glue for 99% of my box joints.

-- "despite you best efforts and your confidence that your smarter and faster than a saw blade at 10k rpm…. your not …." - Charles Neil

View realcowtown_eric's profile


638 posts in 3020 days

#7 posted 03-30-2014 04:22 AM

If yer curious and sincere about box joint jigs you gotta check out this…'

I saw this , had to build iteration 1, and although I had to figure out a few things, got it built, used it.

Totally freaking marvellous.

Invest the time expense to fabricate, learn a few skills along the way.

Yer talking about 1/10th of an inch discrepancey, Mattias is tallking about 24ths of an inch on a rotary dial, so if you can put the handle in approximately the same position, yer talking about 3 or 4 360ths of 1/24th of an inch, and when you do the math, that works out to about 5/10kths of an inch….

Go there, scope it out. The fella is amazaing.

Eric in Calgary

-- Real_cowtown_eric

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