finger joint giving me grief

eagleta2 · Post by **eagleta2** » Sat Dec 22, 2012 8:18 pm

Hi everyone.

Finger joints have been giving me grief... I think most of my problem was because there were no washers beneath my miter gauge tightening knob... there are 2 washers there now.

I am making a new jig... the one that gave me grief last night might have been TOO accurate...is that possible?

I have a new stacked dado...and shipped it to cut a dado that measures exactly .375.

I up cut a the index pin and that measured .375 exactly also (I used 3/4 oak plywood for the fence 5x20 and hard maple for the index pin)

The problem last night was that after cutting the dado, it was basically a pressure fit onto the index pin... it did not slide over it nicely...it had to be forced on. If I wasn't paying very close attention, the board would not be flat with the table because of being hung up on the index pin and therefore the fingers weren't getting cut to their full depth.

Then my miter gauge started to move ( see post in maint section) and since it was 2:30 am and I was frustrated, I gave up,

Tonight I am making a new jig (just the basic non adjustable one that is in PTWFE). I figure we ss folks have the advantage that we can adjust the spading between the dado and the index pin because we can move the quill in small increments.

The question lurking here at the end of this rambling is...

Did I'd make the first jig too accurate? Should I make the index pin undersized a little to make the dados fit over it better? How much do you think? .005"?

Thanks in advance for your help!

Geo

heathicus · Post by **heathicus** » Sat Dec 22, 2012 8:43 pm

I made my very first attempt at finger joints today and had the exact same problem with the very tight fit. I added a 0.005" shim to my stacked dado set and that made a world of difference. The notches fit perfectly over the index pin and the joints fit together snug. Before I added the shim, I had to force the notches over the pin, and the fingers wouldn't even go together.

My box was small, and the fingers were 3/8". Don't know if that would make a difference in how much to shim.

JPG · Post by **JPG** » Sat Dec 22, 2012 9:12 pm

heathicus wrote:I made my very first attempt at finger joints today and had the exact same problem with the very tight fit. I added a 0.005" shim to my stacked dado set and that made a world of difference. The notches fit perfectly over the index pin and the joints fit together snug. Before I added the shim, I had to force the notches over the pin, and the fingers wouldn't even go together.

My box was small, and the fingers were 3/8". Don't know if that would make a difference in how much to shim.

IIWM, the pin would definitely be undersized, but I would be consistent that I took up the 'slop' in the same direction (against the blade side of the pin) ALWAYS. It is the spacing that is critical, not the jig pin size.

charlese · Post by **charlese** » Sat Dec 22, 2012 9:15 pm

Hi Geo! According to Heath, the .005" work well with the wood he is using. Got to consider the species of wood and the width of the grooves/fingers.

Personally, I don't measure that finely. I use a wobble dado blade set at 1/4" measured with a brass bar. The width of the fingers is the hardest to set for me. Depth is no issue, because I make the cuts deeper than 1/4", then sand off the protruding fingers.

Rather than use the quill to set the width between cuts, I have slots cut in my jig and use the handle of a big screwdriver like a hammer to tap the side of the jig to set the final distance. Trial and error.

Also, a larger number of cuts (length of the box joint) makes the set of the jig more crucial. 6" long is a snap, 12" is harder. Here's some of the results. All wood is poplar. This allows for being slightly off, as the wood can be compressed.

[ATTACH]19639[/ATTACH]

[ATTACH]19640[/ATTACH]

[ATTACH]19641[/ATTACH]

[ATTACH]19642[/ATTACH]

P.S. BTW - Like JPG said, if there is slop around the pin - ALWAYS take up the slop in the same direction. The smaller the slop = better fit.

Also I wish we would try to call these joints BOX JOINTS rather than finger joints. Finger joints are sloped and used to make atwo or more boards longer. Like 2X2s

videobear · Post by **videobear** » Sat Dec 22, 2012 10:20 pm

Holy cr*p! That is one fine breadbox!

heathicus · Post by **heathicus** » Sat Dec 22, 2012 11:45 pm

So If I had moved the pin 0.005" closer to the blade and (and shaved off the side of the pin) that would have resolved my problem? It would have had the same effect as keeping the pin and spacing the same and adding the shim to the dado?

burkhome · Post by **burkhome** » Sun Dec 23, 2012 7:48 am

charlese wrote:Hi Geo! According to Heath, the .005" work well with the wood he is using. Got to consider the species of wood and the width of the grooves/fingers.

Personally, I don't measure that finely. I use a wobble dado blade set at 1/4" measured with a brass bar. The width of the fingers is the hardest to set for me. Depth is no issue, because I make the cuts deeper than 1/4", then sand off the protruding fingers.

Rather than use the quill to set the width between cuts, I have slots cut in my jig and use the handle of a big screwdriver like a hammer to tap the side of the jig to set the final distance. Trial and error.

Also, a larger number of cuts (length of the box joint) makes the set of the jig more crucial. 6" long is a snap, 12" is harder. Here's some of the results. All wood is poplar. This allows for being slightly off, as the wood can be compressed.

[ATTACH]19639[/ATTACH]

[ATTACH]19640[/ATTACH]

[ATTACH]19641[/ATTACH]

[ATTACH]19642[/ATTACH]

P.S. BTW - Like JPG said, if there is slop around the pin - ALWAYS take up the slop in the same direction. The smaller the slop = better fit.

Also I wish we would try to call these joints BOX JOINTS rather than finger joints. Finger joints are sloped and used to make atwo or more boards longer. Like 2X2s

That must have taken some concentration to cut the box joints on the curved front on that box.

dusty · Post by **dusty** » Sun Dec 23, 2012 8:16 am

eagleta2 wrote:Hi everyone.

Finger joints have been giving me grief... I think most of my problem was because there were no washers beneath my miter gauge tightening knob... there are 2 washers there now.

I am making a new jig... the one that gave me grief last night might have been TOO accurate...is that possible?

I have a new stacked dado...and shipped it to cut a dado that measures exactly .375.

I up cut a the index pin and that measured .375 exactly also (I used 3/4 oak plywood for the fence 5x20 and hard maple for the index pin)

The problem last night was that after cutting the dado, it was basically a pressure fit onto the index pin... it did not slide over it nicely...it had to be forced on. If I wasn't paying very close attention, the board would not be flat with the table because of being hung up on the index pin and therefore the fingers weren't getting cut to their full depth.

Then my miter gauge started to move ( see post in maint section) and since it was 2:30 am and I was frustrated, I gave up,

Tonight I am making a new jig (just the basic non adjustable one that is in PTWFE). I figure we ss folks have the advantage that we can adjust the spading between the dado and the index pin because we can move the quill in small increments.

The question lurking here at the end of this rambling is...

Did I'd make the first jig too accurate? Should I make the index pin undersized a little to make the dados fit over it better? How much do you think? .005"?

Thanks in advance for your help!

Geo

The key to making good fitting box joints (finger joints) is precision. Once you have decided what size fingers you want (say 1/4"), select the router bit or dado blade that you intend to use and measure it. Do not assume that your 1/4" router bit will measure .25000". What ever it measures should be the basis of all else. The index pin must be the same size. The tolerance that you set at this point determines the fit for the rest of the job. Remember that inaccuracies tend to accumulate. A .005" deviate in the beginning can result in some seemingly huge gaps before you get done.

Good box joints are not for the "quick I gotta get done" woodworker. They do take time.

charlese · Post by **charlese** » Sun Dec 23, 2012 5:10 pm

burkhome wrote:That must have taken some concentration to cut the box joints on the curved front on that box.

No, it is very simple. Here is the trick - The box joints for the curved area are made on the bases of small triangles. The triangle's bases are about 2" each. After assembly, the curve is sanded by removing the edges of the sections.

The hardest box joints are on the back corners. About 15" tall.

charlese · Post by **charlese** » Sun Dec 23, 2012 6:09 pm

heathicus wrote:So If I had moved the pin 0.005" closer to the blade and (and shaved off the side of the pin) that would have resolved my problem? It would have had the same effect as keeping the pin and spacing the same and adding the shim to the dado?

I really don't know! After all the pin does not have to be the exact same size as the dado blade. The pin can be smaller. The really important thing is the distance between the blade and the closest side of the pin is EXACTLY the same as the width of the dado blade. This distance can be set by tapping (moving) the jig containing the pin either away from or closer to the blade. It is also necessary to always butt the work piece against the blade side of the pin before cutting a slot.

I copied this next Paragraph from a box joint web site. Believe me - it works!! This is a quote worth saving and retrieving before making box joints.

"If the pins and notches' fit is too loose, shift the fence so that the jig pin is a tiny bit farther from the blade. Too tight? Move the pin a hair or so closer to the blade. Don't make the joint fit too tight - applying glue during assembly will swell the wood and make the fit even tighter!"