Post your favorite DIY Tablesaw box joint jigs!

[Gary386]

Whatever the jig, it needs to be adjustable by a threaded stop or block. What I mean is, if it is adjusted by loosening, bumping, and tightening, then this can be very frustrating.

If you have a miter gauge with a fence that slides, and you can rig one block on the sliding part, and one block on the fixed part. Then a 1/4" or 3/8" bolt threaded in one, stopped against the other will give you the controlled adjustment that you need.

[Alan in little Washington]

Gary386 said:

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Whatever the jig, it needs to be adjustable by a threaded stop or block. What I mean is, if it is adjusted by loosening, bumping, and tightening, then this can be very frustrating.

If you have a miter gauge with a fence that slides, and you can rig one block on the sliding part, and one block on the fixed part. Then a 1/4" or 3/8" bolt threaded in one, stopped against the other will give you the controlled adjustment that you need.

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I tried that with the jig in my earlier post that had the replaceable sub-fences. The main (fixed) fence had a metal reference "pad" (hex bolt) and each sub-fence had a piece of threaded rod running through it. The end of the rod was the index probe. I cut a slot in the opposite end of the rod I could use a screw driver to fine tune the position of the sub-fence. Theoretically, once installed each sub-fence would always be in the "correct position." However, this was only of limited value since it only affected one of three critical parameters- the blade-to-index pin spacing.

Another problem was getting the dado blade thickness set precisely to the width of the fixed-size index pegs. That often took awhile even though I knew exactly how many chippers and *shims should be used (*Forest dado blades are ground undersize.)

Unfortunately, for a box joint jig to work properly, there are three critical parameters which MUST BE PRECISELY IDENTICAL (to within just a few thousandths of an inch, i.e. +/-.002").

Dado width (width of the actual cut, not the "published width" of the blade) MUST = blade-to-index pin spacing MUST = width of index pin.

That was nearly impossible to achieve and why I trashed that fancy wooden jig and why I designed the I-BOX to reference off the dado cut. The I-BOX doesn't care if the dado stack is not exactly set to some predetermined, precise fraction, it just doesn't need it to be! You adjust the index pin size and its distance to the blade almost automatically at the same time with a single adjustment, since they are linked, by direct transfer of the dado cut measurement! It's quick and easy.

Failed fancy wood box joint jig:

"Metal reference pad":



Sub-fence index probe (threaded rod):



Adjustment end of the index probe on the 1/2" finger joint sub-fence:

[jgourlay]

Alan,

Your last post got me thinking: how many finger widths do you really need? Or, more to the point: if I'm doing smaller boxes or things for the shop, am I really going to need something other than 1/8", 3/16", 1/4" fingers for reasons of strength or asthetics?

It sounds like I'd be better off building a dedicated jig for each bit, and doing this on a router table. Especially given that putting a dado stack into a sawstop has the additional fiddly step of swapping a cartridge.

My prior tablesaw experience is slowly coming back to me in dribs and drabs and starting to recall all dado cartridge work as being a pain.

[jussi]

This looks like an easy but accurate method.

http://www.youtube.com/attribution_link?...Dem-uploademail

[arnman]

A long time ago on this forum (probably around 2000) a member named MadMark designed a box joint jig for use on the table saw that was made from a few pieces of wood, some simple hardware, a threaded rod, and was attached to the miter gage (iirc). A few other members built it and reported very good results. The jig was moved along the threaded rod by turning a handle. The threads (something like 20 threads per inch allowed very good precision). The width of the pins and the spaces were determined by counting the number of handle revolutions.

He sold plans for the jig, which was only to cover copying and postage. I bought the plans but now I can't find them. I never had a chance to build the jig.

I wonder if anyone else rememembers that jig.

[JSpill]

Steve, the jig you described startled my memory. I'm pretty sure the jig you described was called " Lynn's jig." I sent for the plans and hardware and they are hiding somewhere in my basement. If you google "Lynn's Jig" you will find a lot of information. Many people have high praise for it's accuracy.

[arnman]

JSpill,

You are right! It was "Lynn's jig." Named after mssabin, I believe - another long gone woodnet member. Back in those days, I was just a lurker.

I will look into that. Thanks!

[Blacky's Boy]

Originally this jig was meant for a tablesaw. But I modified it to work with a router table. I think the original design came from Wood magazine. This even got featured in a one paragraph article in Wood back in 2006 (or so)

It's got a threaded rod to micro adjust the spacing. Once you dial it in you need to lock it down and away you go! While I built all of the inserts for the sizes up to 1/2" (or was it 3/4"?) I only used the 1/4" and 3/8" ones.

I've used it on about a dozen projects and it's worked flawlessly each and every time

[Alan in little Washington]

One issue with Lynn's jig is that it used a 3/8-16 threaded rod (that is 16 threads per inch) so that you would crank it a certain number of full rotations to make common fractional fingers, e.g. for 1/4" fingers you turned the crank 8 times to move the board(s) 1/2" before you made the second cutting pass, cranked it another 8 times for the next pass, and so on.

If you planned to make 3/8" fingers you would need to turn the crank 12 rotations between each cutting pass and 16 rotations between passes for 1/2" fingers. That is a lot of cranking! If you lose track and mess up just once, you have screwed the pooch for that joint!

Also if your dado (or router bit) is not a multiple of 1/16" for some reason, either because you intentionally chose another size or you did not do a good job shimming, you will need to use whole rotations + one partial rotation of the crank- try keeping track of that. 12 2/3 cranks, plus 12 2/3 cranks- you get the idea. If you computed the number of crank rotations wrong or forget where you started counting rotations, you are sunk again.

Everyone should watch the video at the link that Jussi's posted and note the level of precision used to make the "simple" jig!

http://www.youtube.com/attribution_link?...Dem-uploademail

Speaking of precision, if the I-BOX and other precisely made jigs, are initially set accurately, the joint will be "too perfect" the fingers will be the exact same width as the spaces- and will be too tight because there isn't enough clearance- the video mentioned above addresses this. With the I-BOX all you need to do is just dial in a few thousandths of micro.

jgourlay, it is not so much about how many sizes of fingers you need to be able to make, it is about adjustability. As I mentioned in one of my other posts (it was also mentioned in the video), dadoes don't always stack how you think they will and you can spend a fair amount of time shimming to the size your want. Also, a friend was shocked to find out after he was unable to get his DIY box joint jig to work, all router bits aren't ground precisely either!

[jgourlay]

Alan in little Washington said:

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jgourlay, it is not so much about how many sizes of fingers you need to be able to make, it is about adjustability.

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As my prior router-table-tablesaw experience is coming back to me,I am beginning to remember that the drawback of power tools vs hand tools is....everything is a setup.