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Box Joint jig

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I've never used the incra jig but understand they work quite well.  On the other hand they are costly and I had everything on hand for this.  The incra gives lots of options I don't have with this as far as I understand.


When measuring the distance between each finger joint wont be easy using a standard micrometer.

Calipers work better for this. If your using a micrometer for the resolution, there are actually calipers that measure to the micron level (0.001mm).

However, a bog standard cheap calliper will do the job. 


--- Quote from: jcs0001 on September 27, 2015, 09:26:48 PM ---I've managed to find a number of small instruments for my metalworking hobby - micrometers etc. for very good prices but usually without a box.

(photobucket link:

As you can see one has the original box (a very nice starrett with all the attachments) but the remainder do not.

The starrett boxes (at least this one) have box jointed sides with a tacked on bottom and sliding top.  Quite simple and they don't take up much more room than the micrometer.  A closer view of this one:

I've wanted to build an accurate box joint (sometimes called a finger joint) jig for some time but didn't get it done.  I plan to use it on my tablesaw as it's convenient and accurate (and less noisy than the router).

I did some searching around and found the one designed by the proprietor of  It can be seen here:

It's a very nice jig and seems to be an improvement of Lynn's boxjoint jig.  Lynn's jig is based upon the travel created with a 16 thread per inch rod and this gives quite fine control.

I wasn't sure I needed to get that complex so kept on looking.  Eventually I found this youtube video - a modified Lynn's boxjoint jig and it appealed to me as being fairly simple and easily modified if I choose:

Take a look at all the tools behind Ed when he is talking in the video - unbelievable.

I also found the plans that Ed posted here:

Be aware that there are a few measurements posted that are wrong.  Fortunately I found the errors before cutting any wood.

The finished jig (looking from the back):

Left side view:

Right side view:

I made a few changes as follows:

- installed bearings in the plywood ends to support the threaded rod.  It's 3/8 in. 16 tpi.
- made a threaded insert for the wood piece at the back of the carriage.  It's epoxied into the wood so isn't going anywhere.
- changed the handle to a wheel and indexed it every 10 degrees.

The reason for the indexed wheel is that for small joints (eg. 1/8 in. fingers) I will use a single blade and I don't have one that's exactly 1/8 in.  so I can use the indexed wheel for an extra cut to bring the gap between the fingers to exactly 1/8 in. (or other dimensions if I need to).

I've just built a small box out of some rather crappy plywood but plan to make some out of better material.  Will post the results when I have one or two made.  I did find that once the distance between fingers is worked out it is quite easy to use.


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