Incra I-Box Jig

[jsburger]

By George, John The Incra jig works wonderfully well. Thanks much for taking up the challenge! Sorry about not getting back sooner - other stuff going on here.

Will order soon. I'm sure it will make it easier on long joints than my old hammer tapped system.

Here's a 14" long, 1/4" finger joint made with a homemade fence and tapping sideways with a hammer. Took 4 or 5 samples before it was right. First too wide fingers then too narrow, then a light tap finally got it right.

Magazine boxes.jpg

That sample didn't come about on the first try either. I think it took 3 tries to get the pins right but it was only the second time I had used the gauge. So gauge familiarity was an issue in this case.

[JPG]

He was referring to the 'stackup' deviation due to tolerance that explains why calculating distances(so the end joints are 'equal') rarely adds up or is realized in practice.

Yes, that is it. However, I here is another thought.

I am using a set of Forrest box joint blades. This particular set cuts either 1/4" or 3/8" slots and they are dead on and not adjustable. To get the pins to fit they have to be slightly smaller than the grove. You also need room for glue. So if each pin is 0.001" smaller than the grove you end up short (or long depending how you look at it) about 1/32" at the far end with the 28 pins in this case. With more pin clearance you end up even shorter.

However, if you are using a stacked dado set to cut the groves you can use shims to get almost any width grove. So you should be able to play with the grove width to compensate for the pin fit and end up even on both ends for a specific length. My guess is that it would take a lot of playing around and there may be some specific lengths where you still can't get there.

I assume the 'tightness' adjustment varies the resultant 'finger' width which changes the total 'length' of a set which multiplies with increasing number of sets.(A ;set' is a slot/finger pair). This adjustment is independent from the 2:1 movement of the reference surfaces.

[reible]

I've done a fair number of these joint and the end where you start you can get the tail and pin to align and the joint can be full sized. On the far end to end up with a full joint would be more luck then skill.

Since the two parts are cut at the same time the fit will/should be the same for the whole process. If the joints are loose to start they will be loose the whole way. To tight and more then likely too tight the whole way.

You really and let me add the really a second time, need to make your parts long and then trim and be ready to have something that is not the exact size of matched increments of the joint size.

I'm made my own jigs and used this jig and I've used my other incra and jointech router stuff and none of it has ever done the even increments unless it is very short with only a few joints to cut.

It was interesting that when I started making these with my router and incra router jig (not this one but the LS) that I found I needed to make the cut then back the bit back through the joint cut to get them to work right. This was contrary to what I had been taught but when I talked to an expert on this is what he told me to do, and he was right..... so lesson learned.

I dislike dovetail joints so if I'm doing this sort of joint I go with box joints. I can't even remember the last dovetail joint I did. I do how ever like sliding dovetails and use them regularly.

[reible]

BTW for the newer members here is my first i-box project.

http://www.shopsmith.com/ss_forum/gener ... 13257.html

Ed

[JPG]

. . .

It was interesting that when I started making these with my router and incra router jig (not this one but the LS) that I found I needed to make the cut then back the bit back through the joint cut to get them to work right. This was contrary to what I had been taught but when I talked to an expert on this is what he told me to do, and he was right..... so lesson learned.
. . .

That allows the 'leading' edge of the cutter to work on both sides.

I assume that leads to more repeatable surfaces.

Good to know.

[reible]

. . .

It was interesting that when I started making these with my router and incra router jig (not this one but the LS) that I found I needed to make the cut then back the bit back through the joint cut to get them to work right. This was contrary to what I had been taught but when I talked to an expert on this is what he told me to do, and he was right..... so lesson learned.
. . .

That allows the 'leading' edge of the cutter to work on both sides.

I assume that leads to more repeatable surfaces.

Good to know.

As it was explained to me the wood fibers are compresses as the cut is made, then will expand back out to the tune of a couple of thousands, the second pass cleans that up which is pretty much what you indicted. You can hear the cut so it is indeed doing something.

Ed

[jsburger]

He was referring to the 'stackup' deviation due to tolerance that explains why calculating distances(so the end joints are 'equal') rarely adds up or is realized in practice.

Yes, that is it. However, I here is another thought.

I am using a set of Forrest box joint blades. This particular set cuts either 1/4" or 3/8" slots and they are dead on and not adjustable. To get the pins to fit they have to be slightly smaller than the grove. You also need room for glue. So if each pin is 0.001" smaller than the grove you end up short (or long depending how you look at it) about 1/32" at the far end with the 28 pins in this case. With more pin clearance you end up even shorter.

However, if you are using a stacked dado set to cut the groves you can use shims to get almost any width grove. So you should be able to play with the grove width to compensate for the pin fit and end up even on both ends for a specific length. My guess is that it would take a lot of playing around and there may be some specific lengths where you still can't get there.

I assume the 'tightness' adjustment varies the resultant 'finger' width which changes the total 'length' of a set which multiplies with increasing number of sets.(A ;set' is a slot/finger pair). This adjustment is independent from the 2:1 movement of the reference surfaces.

Exactly.

There are actually two adjustments. The two silver bars in the first picture are what the cut slot fits over. The red knob changes the width of those bars to make a tight fit in the cut slot. At the same time it moves the pair of bars in relation to the blade proportionally depending on the bars width. This sets the pin width.

So far I have seen the pin width start out a little too wide so I need to recheck my calibration. That is not a real problem since the pin width is adjustable independently of the silver bar width. The silver knob adjusts the two silver bars in unison closer or farther away from the blade thus changing the pin width without changing the silver bar fit in the cut slot. The white marks on the red knob are 0.001" marks. The black knob on top locks all the adjustments. The gold try in front slides side to side and once the adjustments are made you slide it tight against the outside silver bar and lock it down.

So in this case we are cutting 1/4" slots but the pins have to be slightly less than 1/4" depending on the tightness you want. As a result each set (pin/slot) is slightly less than 1/2" and the effect is cumulative.

[charlese]

Oh my! The I box must be adjusted? I can understand adjusting between 1/4 to 3/8 to 1/2 inch fingers, but then it must be adjusted to the specific blade that's being used. Should have known that if a 1/4" dado blade is not exactlu a quarter inch, there would have to be adjustment of the jig, but that escaped me for a while. (old age)

Now Ive changed my mind about getting one of these boxes. I love to KIS (keep it simple) with woodworking. Gotta show you my simple jig that works wonderfully well with a couple of hammer taps. And it only cost about a buck. Here is a chest made with that jig