Love / Hate relationship with finger joints

[Geeze]

I love the look of finger joints - I hate the uncertainty of fitting wood together to a complete 'grounded' joint. Currently working on a white oak 2x10 that utterly defeated me last night in two different attempts to glue and beat the joint to together. A bonfire was REAL tempting - while much naughty wordage was mumbled. Disassembled and glue wiped away I fled the shop in defeat. I thus contemplated my wood working navel for the rest of the evening.

Modifying finger joints has been a trial and error - mostly error - as alignment of the file/sandpaper stick/milling machine was critical to joint happiness. The marginal results required slivers of wood [oh how I hate those fiddly bits and slices] or lately the opportunistic [some call it lazy] application of epoxy - still not a solution I was willing to accept.

So here I am in my madness yet again tempting the wood joint gods to smote me. They did.

Sanding seemed to be the best method to remove minute amounts of wood in a controlled fashion. I tried hot gluing sandpaper [150 grit] to two sides of a piece of wood. It would just press fit into the joint requiring a rocking motion to seat into the cut. I noticed two things - the sanding stick cut it's way into the slot and the tight fit kept the stick aligned. Promising until I ran out of glue sticks. No stores open this late at night so I had to wait. Can you believe that Lowe's had the gall to not open their doors to me until 8AM!

Wandering about as I usually do I noticed they did not have the glue sticks in the glue aisle. They did have contact cement - a better solution as the glue thickness could be better controlled. They also had 1/2" pipe clamps. I have a pile of the quick grip style of clamps and they just didn't have the clamping horsepower I required to bend those ornery joints to my will. Like a fool I bought 2. I later went back and bought two more.

I cemented sand paper to two pieces of wood and with the aid of a 1/4" iron bar and some more sand paper shims joint dressing was in full swing. At this point two joints are sanded, glued and mashed flat. Are they perfect? No but they will require much less fixing - always a good thing.

For some my navel gazing revelation is old news but it is worth sharing. If you have wood working tricks/tips please share them - I know I need lots of tricks.

Russ

[xtian]

Well, let's start with, how are you cutting your dovetails?

I use a cheap Harbor Freight jig, and after a few adjustments and test cuts, I can get reliable and snug fitting half-blind dovetail joints.

http://www.harborfreight.com/dovetail-m ... 34102.html

[Geeze]

I use a table saw [no router - yet] and built a jig that cuts 3/4" fingers consistently. What I have found is most solid woods migrate when material is removed. I use highly figured planks 7-11" wide that are rarely flat or square and thus need additional 'help' to play nice in the joint area. Finger joints for me are a decorative features - not a structural necessity.

The ability to remove .002-.003" additional material accurately from the sides of fingers allows me to hand seat the wood to at least 80% - have never been a fan of bashing with a mallet.

I suspect at some point I will acquire a router and open up more crazy and artful joint possibilities.

Russ

[martin manning]

Are you using the usual type of jig, a piece of wood with an index pin attached to the miter slide? If so the way to get additional clearance in the joint is to set the index pin slightly closer than one cutter width away from the cutter, be it a dado head or straight router cutter. That determines the pin width, and so the difference between that distance and the cutter width is the clearance.

[telentubes]

I like the strength of the finger joints but glue up can be a bummer. I try to do one joint at a time to make two halves, then glue the two halves together.
There is a lot of surface area to cover with glue and water based glue makes the wood swell, tightening the joint. Hence reaching for the mallet. Slow cure viscous epoxy works well in this situation. Fills gaps and has lots of working time making glue up of the whole project possible at one time.
I made a jig for my table saw to be used with a dado blade.

[Regan]

Sounds like you are making them too tight!
Keep them a little bit loose, the glue will swell the wood- if they are tight enough you have to hammer them together they are too tight.
Regan

[sepulchre]

@xtian: that's a nice price for jig like that! All the ones I've seen are ~$80. Next time I'm in Harbor Freight . . .

@geeze: Check out this jig. It has a micro-adjustment so you can make the joint as tight or loose as you like. I've been using one and it's been working out great.
The video is in two parts, this is the first part: https://www.youtube.com/watch?v=3xDXePtofxE

I just finished a light table with 3/8" fingers and they were snug but not so much that gluing was a problem. The little adjuster works a treat.

[galtjunk]

Check out the Incra I-box for boxjoints.

You make a single test cut and the jig adjusts to the width of the cut.

It's about $155 but it will work for whatever width you need.
It doesn't get any easier.

http://www.youtube.com/watch?v=VK4JYV2YZbA

[Laurent Brondel]

A dovetail-type jig is the best way to do it, as the cuts will be identical on both pieces, and it's just a matter of offsetting them properly and using the right router bit.
On a tablesaw jig, any discrepancy between cut and spacer is compounded by the number of pins: if the spacer is not exactly what it needs to be compared to the dado width, or if it is a bit loose, every pin cut will add a few thous of misalignment. Of course with softer woods like pine it's easier to hammer the pieces home with a block and mallet, not so with oak.

[sepulchre]

On a tablesaw jig, any discrepancy between cut and spacer is compounded by the number of pins: if the spacer is not exactly what it needs to be compared to the dado width, or if it is a bit loose, every pin cut will add a few thous of misalignment.

True, unless you can adjust the jig. I have a router table. No dove-tail jig but I do have another style of jig for it. It works very well but takes an hour or so to get it set up properly or it has the same problems you said about table saws.

With my adjustable table saw jig it only takes a couple of minutes to set it up and the cuts fit beautifully every time.

That said, I'm sure a really nice dove-tail jig would work even better. But I'm happy with this little jig, and since I made it with scraps I had on hand it was free.

[Geeze]

Thank you for all the great replies and information. Have you experienced that some woods are more joint-able than others?

Here is one of this weekend's joints fresh from glue up.

[Phil_S]

The biggest problem I experience is setting the router bit to the correct depth. It isn't so bad if the parts protrude -- that's what a flush cutter with a bearing on the bottom fixes in a jiffy. It's when they are shallow ;-{

Also, mine always seem to be too tight. I believe this is an alignment problem in my case.

[cbass]

I have to admit I've not done that many box joints but I made a couple of speaker cabs by modifying a jig I made for making dental molding.
Went to gether prettey good.If you are using a junk dado blade and a crappy saw I would imagine it to be pretty difficult.

If you have to beat it together with a mallet its to tight.

I almost forgot. White Oak is hard but I guess you figured that out huh

[Cantplay]

If you end up with fingers a little short...Well, thats what the corner rounding bit is for.

You can use a large radius bit set shallow, and make a pass on each face.

John

[njwrecks]

Maple- used porter-cable jig- did have to use a hammer to put joints together.