Box / Finger joints

[cusimar9]

Apologies for the huge image, posting a photo from my mobile is trickier than I thought!

After many weeks of faffing about making a router table and a box joint jig, I finally have something that resembles a box joint!

It's half inch fingers and, aside from them being a little too deep the fit is very nice.

Though the fingers do give a fairly tight joint you can see small gaps between the fingers. If I wanted an absolutely perfect joint would I be expected to cut the fingers wider and then 'drive' the fingers together with a clamp for a very tight finish?

 

[marcros]

No, I don't think so, although that would do so on the end fingers. It is all about the accuracy of machining. You may find that the glue will fill them anyway if they are finy, so they won't be seen, or you could try preening them gently which can help with dovetails.

How are you cutting them? Are you using a jig of some sort?

 

[cusimar9]

Yes a very basic box joint jig with a straight cutter

 

[cusimar9]

Sorry my question may have been worded wrong. I meant to say should I cut the fingers wider and then drive the joint together with a clamp for a tight finish?

 

[marcros]

I cant quite see from your picture exactly what the error is, but i would sketch it out and exaggerate it. if you are getting gaps top and bottom, it is gutting too wide a gap. If they are wedge shaped gaps, then the cutter isnt perfectly straight as it cuts (is the end perfectly 90 degrees, is the router table flat etc).

I assume the jig is a simple peg that moves along and leaves the width of the cutter as a non cut before cutting the next?

 

[marcros]

ah, i see the question. Yes, you could. There is a very fine line between a bit loose, just right and too tight. A perfect fit should be about being able to tap it together with the palm of your hand. Or you could use a rubber mallet. You certainly dont want to be hammering it together though.

 

[woodpig]

What jig are you using, have you got a picture or a link?

 

[cusimar9]

It's just a very basic homemade jig, I'll post a picture when I get back. In essence it just has a peg which you move the piece along as you go.

 

[fluffflinger]

Steve Maskery of this parish has an excellent box/finger joint jig.

https://www.youtube.com/watch?v=eKEB-BIq9qI

A good accurate jig will work forever with no faffing!

 

[cusimar9]

OK so on the positive results of my first effort I decided to amend the jig I made slightly to make it safer, here is the result:

Having now used it to make 20+ box joints (!) I'm very impressed with it's accuracy and simplicity.

The key to it really is in the micro adjustment. After messing up countless joints I decided to make use of my digital caliper to get the joint accurate to 1/5th of a millimeter. Once I found an accurate way to measure my adjustments it was plain sailing.

Glued and sanded I think this would look spot on. I'll be trying it out in a final piece in the next few days.

 

[lurker]

I use a jig Mailee described in jigs and tips years ago simplicity itself and gives good results

 

[Johnny00]

That was the stage that I reached, then moved on to do the remaining joints on the box and that is where I hit trouble.

The fit between the fingers was ok but the joints didn't line up with the first.

I posted a question under "cutting sequence" and got some very useful replies, they may be of some help

 

[rafezetter]

I cant quite see from your picture exactly what the error is, but i would sketch it out and exaggerate it. if you are getting gaps top and bottom, it is gutting too wide a gap. If they are wedge shaped gaps, then the cutter isnt perfectly straight as it cuts (is the end perfectly 90 degrees, is the router table flat etc).

I assume the jig is a simple peg that moves along and leaves the width of the cutter as a non cut before cutting the next?

I was going to suggest the same thing and also a test to see if the cutter itself isn't somehow not perfectly machined. Pry apart this joint, or cut a few fresh ones and then size the cuts against the cutter itself to see if the cutter is scraping the sides of the cut at all points.

If it's a more budget cutter and was machined by even 0.01mm off centre, you'll get that "sloppiness" from the wobble. Of course it depends on how perfect you want them, but I can thoroughly understand the desire for the best results. Resintite glue mixed with a few dye crystals could be an option, or investing in a really good quality cutter from somewhere (brains telling me wealdons?) if you are going to be using this method regularly and don't want to keep cleaning them up by hand (I'm prolly telling you how to suck eggs but just in case ) Also, just in case, examine your jig to make sure all the important bits are correct.

Looking at the picture it looks as though the cut is ever so marginally wider at the base than the top meaning the finger ends have gaps. (at least that's what it looks like to me)


Edit: darn, should have read whole thread before replying - looks like you have it sorted although... can I see that the joints are still ever so slightly loose? That last pic of a new set looks like one of the boards can lean at an angle instead of being held to 90deg? Or is that my imagination?

 

[WoodMangler]

Steve Maskery of this parish has an excellent box/finger joint jig.
https://www.youtube.com/watch?v=eKEB-BIq9qI
A good accurate jig will work forever with no faffing!

I agree with this - easy to make, easy to use, makes joints that fit - well done Steve.

 

[Wildman]

the vid by Steve is excellent thanks for posting it.