Finger Joint Pitch

[The Dougster]

I have got 2 each 1 x 2 x 4' 2" and 2 each 1 x 2 x 2' 2" maple for my coffee table frame and I would like to finger joint (box joint) the corners with an odd number of tabs so that the longer front rail has top and bottom tabs. I just can't decide on 3, 5, or 7 fingers. Or even maybe 9 fingers about 1/4 thick. I will do the dados on my drill press with saw arbor, blade, and cross vise.

Can you help?

Here's what I have found in this group:

Goncz Replikon Research Seven Corners, VA 22044-0394

[Leon]

>> Doug Goncz

The number really does not matter. Pick a number and go with it. Keep in mind that the more fingers that you have the stronger the joint will be.

[Robatoy]

I read somewhere that for maximum strength, the fingers should not be narrower than the thickness of the material used. Ever hear of that? In an intuitive way, that sorta makes sense.

r-----> who will be thinking about this all day and probably testing later this week.

[Leon]

I am not sure I would agree as true finger joints, not box joints, are quite thin and quite strong. Some of the framing lumber is made up with thin finger joints. Typically, regardless of the width of the finger you end up with the same mass of wood with thin fingers as the wide fingers. The wide fingers have less surface area with glue.

[Robatoy]

In an end-end tapered finger joint, I can see where many long skinny fingers would make a better joint. My reference was more a box joint at 90 degrees. Can the 'fingers' be too thin? In my mind, such as it is, if taken to the extreme, one could reduce the thickness of the finger in a box joint, to the point where you might as well use a butt-joint. Do I need more coffee?

r

[Leon]

LOL..

Yeah, you really do not see finger joints on anything but straight in line unions.

Again, I don't think so, while they are thinner and therefore weaker you have more of them. If the box joint finger is made 1/4 the size you have

4 times as many. Again, the mass is still there. IMHO ;~) Thinner ones would spread the load more and perhaps be stronger.

I need coffee.

[Mark Blum]

I don't think that recommendation is for strength at all, but rather for a balanced-looking joint. Box joints seem to look best when the fingers of a joint look almost square when viewed on-end. It isn't a hard-and-fast rule, but skinny fingers on a thick board just don't look as good as thicker fingers.

I think the joints should be balanced between the thickness of the wood and the width of the wood, since narrow boards look better with smaller fingers. As for the OP, assuming he is using 3/4" stock, of his listed options I would probably go with 5 fingers (4 on the front rails and 3 on the side rails.) I don't think 3 would look right on such narrow stock.

-Mark

[Robatoy]

Yabbut... you can't expect more than the strength of the wood itself. Soooo... the more you leave untouched, the stronger it is? I mean, if you look at the strength of an single finger (from a row of fingers). the smaller the finger, the weaker, right?

Visually, I agree with Mark, square looks nicest. I have always liked the look of that. I find the whole dove-tail overrated, other than the obvious advantage in a drawer front.

My oldest daughter set a date for her wedding (Fall 2007) and she would like an heirloom piece. I will be focusing on wood-dorking this year. I was thinking a stack of barrister book-cases, so nice looking joints are on my radar.

r

[The Dougster]

I have redesigned the legs and joint. The legs (made of 1/8 x 1-1/2 inch aluminum angle) now cover the joint so appearance doesn't matter. I am considering knockdown construction with a 1/4 inch dowel through the fingers which are at the moment 5/8 x 5/8 and 1/3 inch thick and 3 each #8 t-nuts on each face. (5 fingers total) The legs will taper to

5/8 tips and may have "lightening" holes the way they do in aircraft construction, strictly for appearance.

I am using emachineshop software to visualize the joint and legs. I can post a PDF of the 3D views if anyone would like to see that. That much was a lot of fun.

Maybe I should miter the joint tops for appearance, but I will probably get a better fit with square joints since the milling machine (made from a drill press) doesn't cut miters. I am working on building one that does.

The holidays were rough and the weather here is fine today so I am going to get some exercise now on my bicycle.

This will a Seasonal Affective Disorder coffee table 2x4 feet with 128 watts of T8 tube in it. That's 10,000 lux! It works for me and my sweetie in the mornings. The fixture will just drop into the frame and needs a plate glass top. It's a nice "light table" for assembling patterns and such as well. The fixture sits on boxes now.

Doug

[Swingman]

IMO, for box joints to look "nice" on fine furniture, the wider the better ... AAMOF, they will appear more like dovetail joints from all sides if you use as few as possible, say 3 "pins" on each board at the corner of a

12 -15" wide join.

That said, this is purely a matter of taste ... I'm not a big fan of the box joint, except on tool/shop boxes. ;)

[Robatoy]

Why didn't you say so right off the bat? I would have suggested dove-tails....... using real doves.

r

"I'm on my second cup of coffe, I still can't face the day...." ..waitasec... there's a song in there...*grabs pen*

[Father Haskell]

Through dovetails preferrably (lock rabbet usually, because it's fast and adequate for the piece), except in narrow stock. It's easier to cram more fingers than tails and pins into 1 x 2 stock.

[Father Haskell]

Vary the pin widths and / or spacing to add interest. You'll have to lay out the joint by hand and cut the slots by eye, but the result might be worth the hassle.

[The Dougster]

Thanks for a lively and interesting thread.

I am going with DFM (Design for Manufacturability) since the joints will be hidden. So that is three fingers on each member, at quarter-inches, with a dowel through the fingers, and the wrap-around legs adding security. It'l be easy to dado out and refine the fingers with this layout and the machine I have. It'll be hard to place that dowel but a jig will take care of that.

Never do the math in your head:

That's 6 fingers of 1/4 inch making 6/4 or 1-1/2 inches. OK, I did get it right. They are 5/8 square fingers with the 1/8 angle recesssed into the ends of the 3/4 inch stock. (1 inch nominal maple 1x2 from Home Depot) The legs are going to be 1-1/3 feet long (1' 4") adding to 4' for packing when I move later. I'll get a shipping tube for the parts.

Would anyone like me to upload some 3D PDFs to my web site, and some pictures later?

Doug

[The Dougster]

OK, here are PDFs of the Seasonal Affective Disorder Coffee Table joint and leg, even thought nobody asked:

[Prometheus]

My box joint fingers are 3/32" thick, give or take- that's the thickness of the kerf on my freud blade, and the joints are about as tough as anything you can make. Making them thinner than that seems like a tall order, though I suppose it could be done with a bandsaw if a guy were inhumanly patient.

[Larry Kraus]

to get together with your marketing people to find a better name for your furniture style. Somehow, SAD just does not have the appeal of Chippendale or Queen Anne... Especially if you are offering it for sale with "Type A Suicide Cord" !!

[The Dougster]

Thanks for browsing. Those are no longer for sale.

Anybody have a name?

Bright Table?

Coffe Light?

Doug

[The Dougster]

I have ordered a box joint cutter for $24.95. It has five blades 5/32 inch. It should do nicely. I have updated my PDF locally but not on the FTP site.

Doug

[The Dougster]

The new cutter is a delight and box joints proceed with a 10-24 pin screw through the fingers. Very nice. I have a long nut tap coming to finish these threads in the wood.

I would like you all to comment on how a 4 inch cross vise might clamp such a joint for drilling that pin through the leaves in such a way that the fingers were forced tightly together by the clamp. Sort of a big vee to take the legs, and little knives to grip and force the wood inwards?

Doug