Box Joint Troublle - Woodworking Talk - Woodworkers Forum
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post #1 of 13 Old 09-18-2019, 08:32 PM Thread Starter
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Box Joint Troublle

Hello
I have been a home woodworker for years, but I'm pretty set in my old ways. Recently I tried to create a box using box joints.
I read and watched all the videos and made a jig for my router table. It worked great.
One thing I don't understand and maybe someone can help.
The fingers on the joints don't line up.
I mean the first one down to the fourth finger will fit fine, then they or off where they don't line up anymore.
I am totally baffled by this. The jig hasn't moved, It got me. Hopefully I'm missing something simple
Any help would be appreciated.
Thank you in advance
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post #2 of 13 Old 09-18-2019, 09:38 PM
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My guess is that the spacing between the bit and key is incorrect. The router bit, the key, and the space between them all have to be exactly the same.


In woodworking there is always more then one way to accomplish something.
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post #3 of 13 Old 09-19-2019, 08:41 AM
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@Terry Q is right. The router bit (or table saw blade), the key, and the gap must all be exactly the same width.

One thing that I do not understand is the fingers and cuts do not appear to be the same width across the boards. The cuts seem wider on the left side than the right side. (... or the fingers seem wider on the right side than the left side.) Why? You could argue that it is caused by thermal expansion of the router bit, but it seems like way too much for that. I hope it is a photography artifact.
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post #4 of 13 Old 09-19-2019, 10:19 AM
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Vincent, Watch this video.
https://www.bing.com/videos/search?q...6&&FORM=VRDGAR
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Gary
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post #5 of 13 Old 09-20-2019, 10:21 AM
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Vincent,
I believe the root of your problem is compounding error, your key/spacing is off a small, very small amount. The first few fingers aren't noticeable, but each finger's error is added along with the sum of the previous finger errors. Move the key a small, very small distance closer to the dado blade.
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post #6 of 13 Old 09-20-2019, 11:11 AM
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The best jig for box joints that I have ever seen is in this video.
If you want to see the KEY part of it, skip to 11 minutes 30 seconds in. Then if you think its good, go back and see how he makes it.
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post #7 of 13 Old 09-20-2019, 01:47 PM
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in addition to the comments above. i have found that you have to apply consistent "English" on the board as it is held against the pin, throughout the entire process. say left or right, to take up the gap between the pin and the last slot that was cut.

(one hundredth of an inch) .01" off times 20 = 2/10" (over 1/8")

Last edited by TimPa; 09-20-2019 at 01:49 PM.
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post #8 of 13 Old 09-20-2019, 02:39 PM
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Great video thanks for sharing
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post #9 of 13 Old 09-20-2019, 08:47 PM
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The cuts look very strange to me. I am still confused about:

* How does the cut width appear to vary so much, considering that we are using a straight router bit on a router table?
* Why do the tops of the cuts not appear to be flat? They almost look like the cuts were done on a table saw with an ATB blade.

One thing is obvious. The cuts on the top board are not consistent. It looks like the board was not seated fully flat on the table for the shallower cuts.

Could the board be misaligned or moving during the cut? Could the board be not seated flat against the fence as well?
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post #10 of 13 Old 09-21-2019, 02:03 PM
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I have cut many box joints in my woodworking life using many different shop made jigs, and now using an Incra I-Box jig on my table saw. I never had very good luck cutting them on a router table because the bit cuts in both directions, causing chipping on both sides to the board and a slight sideways pulling as it cuts, causing a wider cut if the board isn't held tight enough. A table saw only cuts in one direction, so a sacrificial board can be used to protect the side of the board where the blade exits, keeping the cut edges crisp much like a zero clearance insert does for general cutting on a table saw.

After buying the I-Box jig all of my box joint jigs that I had made ended up in the firewood pile. Some worked OK and some not so great. The Incra I-Box is adjustable and easy to calibrate, so my box joints of any size from 1/8 - 3/4" or more always fit great. I added a Freud SBOX8 for 1/4 & 3/8" box joints and the blade cuts perfect square box joints. An integral sacrificial strip of 1/4 MDF in the jig serves to keep the cuts crisp with no chipping and is easily moved and inverted so a new spot can be used for each use and it can be used many times before needing replacement.

I was once told "You can't cut box joints in plywood", but I now do it frequently in Baltic Birch plywood with no chipping or de-lamination. Attached are a few photos of this. I make a lot of boxes, and prefer using the box joints for most of them, although I do own a Leigh D4R dovetail jig, but tend to only use it for drawers or fancy boxes.

Charley
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post #11 of 13 Old 09-21-2019, 02:37 PM
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CharleyL
nice work, really like it
have you tried box joints on the Leigh D4R?
Wondering as I have a D3 which came with the F1 jig.
thanks
Ron
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post #12 of 13 Old 09-21-2019, 05:35 PM
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I agree 100% with NoNails

My box joint jig is adjustable. Just adjust a hair either way. This requires you make some test cuts.

A word on JIGS: In order for a jig to work properly, you must put as much love and care into it as if it were a fine piece of furniture. Any effort short of this, is a waste of time. Trust me, it took a while for it to really sink into me.
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Retired woodworker, amongst other things, Sold full time cruising boat and now full time cruising in RV. Currently in Somerville, Tx

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post #13 of 13 Old 09-21-2019, 09:05 PM
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Quote:
Originally Posted by evilboweivel View Post
CharleyL
nice work, really like it
have you tried box joints on the Leigh D4R?
Wondering as I have a D3 which came with the F1 jig.
thanks
Ron
I have a Leigh Box Joint finger assembly for my D4R. I used it a couple of times before getting the Incra I-Box jig and haven't used it since. It works fine, but it too had problems with chipping as the bit cut both ways through the wood. The spacing is spot on though. A sacrificial strip is really needed for both sides of the wood being cut. I wouldn't even try it on plywood, only end grain solid wood. I'll make you a good deal on it, if you want it. Send me a PM if interested.

Charley
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