Incra I-Box Jig

[JPG]

Here's a challenge for your new jig, John.

Can you make a 1/4" box joint that fits well and is 14 inches long?

I ask this because I'd like to see if it is as accurate as my method of tapping a homemade jig with a hammer.

If your jig will let you produce a 14" long box joint, I will buy one and also sing it's praises.

By the way - I always plan for, and saw my box joint fingers long! That allows me to sand off the protrusions flush.

So shopsmith should be seeing an order soon?

Ed

As soon as he recovers from passing out after seeing that pix.

[jsburger]

Here's a challenge for your new jig, John.

Can you make a 1/4" box joint that fits well and is 14 inches long?

I ask this because I'd like to see if it is as accurate as my method of tapping a homemade jig with a hammer.

If your jig will let you produce a 14" long box joint, I will buy one and also sing it's praises.

By the way - I always plan for, and saw my box joint fingers long! That allows me to sand off the protrusions flush.

So shopsmith should be seeing an order soon?

Ed

As soon as he recovers from passing out after seeing that pix.

I guess he is still passed out or been out of town. It has been 3 days.

charlese, if one lays down a challenge then one should respond to the results.

[dusty]

Too bad the fingers aren't the same size at both ends. It would then appear to be perfect.

You could always trim the long end to make them the same but then it wouldn't be 14".

Incra does a great job.

[jsburger]

Too bad the fingers aren't the same size at both ends. It would then appear to be perfect.

You could always trim the long end to make them the same but then it wouldn't be 14".

Incra does a great job.

Well, what does 14" have to do with anything other than charlses arbitrary number.

Incra says in their manual that you can try to calculate the width of the stock based on the width of the pins/groves but that it never works correctly. Why? I don't know other than the tightness of the fit and the total length of the joint.

Remember, the stack up as you are seeing in your quest for perfect end table alignment.

Incra suggests exactly what you said. Make the piece wider and trim it. They do provide a large chart with pin widths and stock widths.

Now, consider this. 1/64" is .0156" and there are 28 pins in that 14" joint. If I am off by only .001 then that ends up almost 1/32" at the far end.

If I am off by .005 which you have said is "close enough for Government work" that is .14 in 14". more than an 1/8". Also, as you have said, this is wood. How close do you have to be? In some cases real close but there are ways to compensate.

The point is that it is a perfectly fitting box joint regardless of charlses arbitrary 14" requirement. That is what he asked for.

[charlese]

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 (118.58 KiB) Viewed 8295 times

[dusty]

Too bad the fingers aren't the same size at both ends. It would then appear to be perfect.

You could always trim the long end to make them the same but then it wouldn't be 14".

Incra does a great job.

Well, what does 14" have to do with anything other than charlses arbitrary number.

Incra says in their manual that you can try to calculate the width of the stock based on the width of the pins/groves but that it never works correctly. Why? I don't know other than the tightness of the fit and the total length of the joint.

Remember, the stack up as you are seeing in your quest for perfect end table alignment.

Incra suggests exactly what you said. Make the piece wider and trim it. They do provide a large chart with pin widths and stock widths.

Now, consider this. 1/64" is .0156" and there are 28 pins in that 14" joint. If I am off by only .001 then that ends up almost 1/32" at the far end.

If I am off by .005 which you have said is "close enough for Government work" that is .14 in 14". more than an 1/8". Also, as you have said, this is wood. How close do you have to be? In some cases real close but there are ways to compensate.

The point is that it is a perfectly fitting box joint regardless of charlses arbitrary 14" requirement. That is what he asked for.

Yes, you have created perfectly fitting box joints using the Incra Jig. Where is the "stack up" to which you refer?

[JPG]

Dusty, you removed your response to this initial post, so I also 'deleted' mine. I misunderstood your comment.

[dusty]

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.

Maybe I don't know how the Incra Jig works. When you are cutting the finger joints, do you not start at one end and work your way to the other end.?

If you do that, the first set of pins and tails would be perfect. If there is any stack-up it is not revealed until you cut the last pin/tail. I don't feel that we are using the term stck-up correctly. If you have stack of, each pair of pins/tails fit a bit more poorly than the previous until it is so bad that the pieces don't mate at all. I've done that many times due to sloppy setup.

http://www.shopsmith.com/ss_forum/gener ... 4-s20.html

[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.

Maybe I don't know how the Incra Jig works. When you are cutting the finger joints, do you not start at one end and work your way to the other end.?

If you do that, the first set of pins and tails would be perfect. If there is any stack-up it is not revealed until you cut the last pin/tail.

I think we discovered a forum glitch. If one 'quotes' a post while the original poster is editing it, you are informed the original post does not exist.

To get an even balance on both ends, the initial setup must be different from the intervening repetitive cuts.

You are correct that not doing so will result in the last 'set' being an odd dimension.


I think predicting the end result of the individual finger sets would be quite difficult due to the 'stackup' or variation of execution results vs intended results.

[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.