how to route small finger joints - Router Forums
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post #1 of 38 (permalink) Old 03-13-2020, 12:47 PM Thread Starter
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Default how to route small finger joints

I have a machinist's level that goes in a box. The box is damaged and I'd like to make another one, or at least repair the existing one. I have 2 questions:

1. I've included a picture showing the size of the finger joints. What would I use to make these? I have a Leigh jig, but I don't think I can route fingers this small. Would I set up a dado blade and use a fixture of some sort to get the correct and even spacing? They seem to be exactly 4mm, which is odd because this is an old American level (Starrett #98). However, they could be 5/32 which also seems like an odd number to use.

2. I'm also going to use oak because I have some. I think the original box is mahogany, but I'm not sure. Anyone see any issues with this?

Thanks!
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post #2 of 38 (permalink) Old 03-13-2020, 01:04 PM
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The easiest is with a dado blade and size is pretty much immaterial. I saw a video of someone who did some crude testing with different size fingers and a press with a pressure gauge to see how much pressure it took to destroy the joint with different sizes of fingers and there was very little difference between any of them. So make them with what ever is convenient for you.

There are quite a few articles on making a jig and also quite a few videos on the same. Just google box joint jig and finger joint jig. Both terms are used for the same thing. If you think you might want to do lots of them then I recommend either the Incra I box jig or an LS positioner. Here`s a link to a magazine article showing how to make one. It may require some fine tuning after to get the spacing right. https://www.woodmagazine.com/woodwor.../box-joint-jig

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #3 of 38 (permalink) Old 03-13-2020, 01:23 PM
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my 1st choice would be to use the table saw and a shop made sled to make those box joints.....
Here's some ideas to work w/....

.
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File Type: pdf How to Build a Simple Box-Joint Sled.pdf (1.00 MB, 47 views)
File Type: pdf box-joint-jig.pdf (91.7 KB, 43 views)

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post #4 of 38 (permalink) Old 03-13-2020, 02:56 PM
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I just got this video in my emails from Fine Woodworking and it may be easier to follow. https://www.finewoodworking.com/2012...&mid=943761398
At the beginning he says you need a box joint saw blade but a dado blade is just as good. In the above mentioned strength test the person doing the test even tried one joint with eigth inch fingers which you could do with a full size flat top ripping blade but there was no strength advantage to doing that and it was more work.

The first critical part of doing this is to get the key exactly the same size as the thickness of the blade(s). That`s easy to do by cutting a groove and then work on the key until it perfectly fits the groove. The video shows how to make adjustments after doing a mock up with scrap.

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post #5 of 38 (permalink) Old 03-13-2020, 03:46 PM
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I do lots of small finger box joints with my Incra LS Positioner. Makes it amazingly easy. Here's one with 1/8" fingers.
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post #6 of 38 (permalink) Old 03-14-2020, 07:38 AM
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Really huge fan of my Incra LS Positioner on my table saw. I have the Wonder Fence as well for making the joints, both dovetails and box/finger.
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post #7 of 38 (permalink) Old 03-14-2020, 12:16 PM
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You have received some great advice on making a box joint jig. There are several slight variations, but all will produce good results if you can get them adjusted just right. I strongly suggest that you get yourself a dial or digital machinist's caliper, because you will need the wood pin, the blade, and the space between the pin and the blade to be accurate withing a few thousandths of an inch. You cannot do this with a tape measure. Without one, you will likely spend all day making scrap, trying to get everything adjusted just right. The jig that @Stick486 posted is a very good one. It even has the replaceable sacrificial strip. You will need a new one of these each time you change the blade height position or change the blade. It keeps the blade from chipping out the back side of your work piece as the blade teeth exit the wood. You can use a dado blade, but the bottom of the cuts are frequently not flat using them. They sell Box joint blade sets that cut 1/4 & 3/8" box joints that are perfect, but for 1/8" box joints, I use a Freud Ripping blade that has a flat square tooth FTG grind and it makes great 1/8" box joints. You may already have a ripping blade with these square cut teeth. ATG Alternate Tooth Grind combination blades do not work very well for making box joints. I have tried about every other way to make box joints and the best and cleanest cuts have been with the table saw, the right blade, and a good jig with a sacrificial insert.

I make a lot of boxes using box joints of different sizes. If you are like me, you will end up getting the 1/8" FTG Ripping Blade and a 1/4-3/8" box joint blade set plus an Incra I-Box jig like I did, because I make a lot of box joints of different sizes and the I-Box jig is so easy to adjust, but don't spend all this money now. You can get very good box joints for this small box using a good ripping blade and a shop made jig. Tight fitting joints are achieved by building the jig accurately.

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post #8 of 38 (permalink) Old 03-14-2020, 12:25 PM
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another plan to add to the mix...

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This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

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post #9 of 38 (permalink) Old 03-16-2020, 04:22 PM Thread Starter
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Thanks to all for your ideas and suggestions. The videos were also very helpful. The Incra Positioner sounds really cool, but it's out of my budget and I don't make enough of these to justify it anyway (not that that would stop me, but the Budget Committee President, aka Wife would not approve!).

It sounds like they do not make dovetail jigs this small (I didn't think so, but I thought I'd ask), so I will use one of the sleds mentioned above.
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post #10 of 38 (permalink) Old 03-16-2020, 04:37 PM
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So guys, why wouldn't you use a finger-joint router bit?
I understand the use of the table saw, but I'm confused as to why you wouldn't use a bit in the router? Fully adjustable, repeatable..... Yes, you'd need a backing block to reduce tearout (no different to the table saw it seems), but I'm struggling to understand they "why not"?
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