Finger Joints & Plywood - Router Forums
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post #1 of 35 (permalink) Old 07-07-2018, 06:54 AM Thread Starter
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Default Finger Joints & Plywood

Well as I hone my old rusty skills and learn new ones I have started another project for my shop by way of a hanging tool cabinet. The plans I'm using are from a Woodsmith book titles Shop Cabinets & Tool Stands. In this plan the box sides are all hardwood while the door panels and back are plywood. As I'm a bit short on hardwoods at the moment and have 10 sheets of plywood I asked myself why not make it all from plywood? I have an Incra IBox Jig which I've had very little practice with but am wondering if plywood could work well for this joint? I can't imagine a reason not and research hasn't turned up any negatives but I'd like to ask those who have the experience for suggestions. And yes, I can get hardwood but I thought the ply is cheaper, already on hand, and maybe a good practice exercise that may turn out just fine. Any thoughts?
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post #2 of 35 (permalink) Old 07-07-2018, 09:24 AM
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poor quality limited ply plywood can easily turn in an exercise in futility...
clean your cutters often because of the glue...
rapid tooling dulling is a given because of the glue also...
make sure your tooling is as sharp as it can be...
waste boards are a must...
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post #3 of 35 (permalink) Old 07-07-2018, 10:16 AM
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Trying to make box joints in shop-grade plywood is an exercise in frustration. I used waste boards on both sides, I used the best all-carbide up-cut bit I could buy, I made my jig with as much precision as I could muster, and I still cut hundreds of failures. Mostly because of tear out. The shop-grade ply glue is not good enough to hold the laminations together under the cutting stress, and the voids in the ply ruin the fingers.

If you insist on using plywood, use high quality Baltic Birch (Russian) plywood and as Stick says, clean your cutter frequently.

Best of luck!
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post #4 of 35 (permalink) Old 07-07-2018, 10:21 AM
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For shop stands and cabinets, using regular, 5-7 layer, 3/4 ply, I'd skip the box joints and go to another kind of joint. If you use Baltic Birch, which has about 13 layers and no voids, you could use box joints, but I don't know whether you'd like seeing all the layers every other finger. For all ply cabinetry, consider using dados and rabbits, or even easier, pocket holes (with glue).

Pocket holes have to be drilled in places where they won't be seen, or filled in. They are plenty strong if installed every 5 inches or so. Make certain your saw blade is 90 to the table and the fence 90 to the blade, pocket holes will then pull your cabinet or stand square, and pocket holes do the same to 90 degree cuts to face frame rails and stiles.

Rabbit and dado construction is quite nice for cabinets as well, but you need to make certain they are held square during glue-up.

When you make tool stands, consider adding casters, two fixed on the back, 2 swivel with both wheel and swivel locks so you can prevent movement when in use. Put doors on all cabinets and stands, it will help keep sawdust from invading every nook and cranny.

I've built a lot of stands for my tools, every one with doors. I've used both the metonds (dados/rabbets, pocket holes) and all stands are ridgid after years of use. For no particular reason, I use spherical 1.25 inch knobs painted a very intense, high gloss Ferrari red--it's cheerful.

I also have the same jig, but most of my projects are BB ply these days. BTW, you could make the cabinet out of carefully selected pine, stained, it will look pretty nice. HD has some 1x4 by nearly an inch thickness. Pick nice pieces, joint or cut a flat edge, cut the other edge flat, and use them to glue up your panels. These have very small knots that stay tight, and the extra thickness lets you plane to even everything up. If you're fussy and lucky, you can find some clear pine that's straight, but you might have to visit several Orange stores to find the number of pieces you need. I generally make face frames from nice straight pieces of hardwood. Again, pick the pieces carefully, or even cut them out from straight, flat sections of larger pieces. Then box joints make sense, and you can enjoy using that great jig-just buy enough wood so you can make some test joints to tune the jig.

Stick's admonitions apply.
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post #5 of 35 (permalink) Old 07-07-2018, 10:33 AM
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I did something vaguely similar, using plywood, years ago. Well, it was a toy box, which is vague enough. Around 20 years ago in fact. I just used glue strips on the inside. And still holding up, still being used.

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post #6 of 35 (permalink) Old 07-07-2018, 10:34 AM
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I have two questions:

1- Are you making box joints or finger joints? To me, for joining box corners, you want to make "Box Joints". Box joints have square ended pins and are used for making box corners.. Finger joints have tapered pins and are used for joining boards end to end to make the resulting board longer.

2- What kind of plywood do you have?
You will need "void free" plywood for making boxes and cabinets using "Box Joints". Baltic Birch and Marine quality plywood has no internal voids so they do well for making boxes and cabinets. Construction plywood has internal voids and does not make good joints with the Incra I-Box jig.

I use my Unisaw with My I-Box jig because I've found that I can get cleaner cuts using my saw and the SBOX8 blade than I was able to get easily using the jig on my router table. This is because the saw blade cuts in only one direction as it passes through the work. A sacrificial piece in the I-Box jig becomes a zero clearance insert, keeping the blade from breaking the edges of the cut on the back side. When cutting with a router bit, the rotation of the bit cuts in both directions as it passes through the work. To get chip free edges on both sides of the cut, a second sacrificial piece must be added to the back side of the work as well, so both sides are protected as the cuts are made.It can be done, but I find that it's easier, faster, and produces better results if I use my I-Box jig on my table saw.

Earlier this year I made about 20 boxes from Baltic Birch plywood, joining all of the corners using my I-Box jig on my Unisaw. I had perfect results. Plywood can be used to make boxes and cabinets, if the plywood is void free and you use sacrificial pieces to prevent tear-out. If your plywood isn't this good you should find another way to join the pieces. Solid wood corners with plywood panels between is one way.

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post #7 of 35 (permalink) Old 07-07-2018, 11:37 AM
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I agree with Charley on using a TS to cut the fingers. The saw blade only puts pressure back and slightly down. When a router bit enters the wood the left side is spinning outward which wants to tear the grain on that side and when it exits the cut the right side is trying to do the same thing. Both machines can make fingers but the saw does it better so why use a router?

My daughter needed some bench/storage chests to use as storage and seats around her dining table a few years ago. I used some 1 1/2" square pine for corners which I put stopped rabbets in which made the upper portions L shaped. I then glued and screwed 1/2" mdf panels into the rabbets. Along the top and bottom of the mdf sides I trimmed it with 1/4" wood to improve the looks of it. They looked pretty good and they held up close to 500 lbs when used at the table. So that's an alternate possibility for you that will hide the edges of the ply, nit involve cutting fingers and have the plys exposed and is fairly easy to make. You don't need much solid wood to do it either.
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post #8 of 35 (permalink) Old 07-07-2018, 12:05 PM
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I tried using the router table but the blow out was too bad so I started using my TS. I made this box with my TS and Russian 1/2" Baltic Birch.


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post #9 of 35 (permalink) Old 07-08-2018, 07:07 AM Thread Starter
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Quote:
Originally Posted by CharleyL View Post
I have two questions:

1- Are you making box joints or finger joints? To me, for joining box corners, you want to make "Box Joints". Box joints have square ended pins and are used for making box corners.. Finger joints have tapered pins and are used for joining boards end to end to make the resulting board longer.

2- What kind of plywood do you have?
You will need "void free" plywood for making boxes and cabinets using "Box Joints". Baltic Birch and Marine quality plywood has no internal voids so they do well for making boxes and cabinets. Construction plywood has internal voids and does not make good joints with the Incra I-Box jig.

I use my Unisaw with My I-Box jig because I've found that I can get cleaner cuts using my saw and the SBOX8 blade than I was able to get easily using the jig on my router table. This is because the saw blade cuts in only one direction as it passes through the work. A sacrificial piece in the I-Box jig becomes a zero clearance insert, keeping the blade from breaking the edges of the cut on the back side. When cutting with a router bit, the rotation of the bit cuts in both directions as it passes through the work. To get chip free edges on both sides of the cut, a second sacrificial piece must be added to the back side of the work as well, so both sides are protected as the cuts are made.It can be done, but I find that it's easier, faster, and produces better results if I use my I-Box jig on my table saw.

Earlier this year I made about 20 boxes from Baltic Birch plywood, joining all of the corners using my I-Box jig on my Unisaw. I had perfect results. Plywood can be used to make boxes and cabinets, if the plywood is void free and you use sacrificial pieces to prevent tear-out. If your plywood isn't this good you should find another way to join the pieces. Solid wood corners with plywood panels between is one way.

Charley
For some reason I called them finger joints when indeed they are box joints. As for tearout I didn't get any. With the Incra jig I made sacrificial fences to reduce/eliminate the tearout and that has worked extremely well. I move the fence for each new width cut. So if I'm making a 1/2" cut I'll have a new area that's not cut, lock the fence, amke my cut and continue. If I need to change the cut width I'll set the blade width, and make a new cut into the fence (on the IBox jig). My biggest issue was the joints on the test pieces were way too tight to allow any glue.

As for the plywood, I've not seen a single void or football and it's rated AA. At $56 a 4x8 sheet I seriously doubt it's Russian Birch. I'm not even sure I could find that within a reasonable drive from home. I do have the IBox jig as mentioned and was actually a little surprised to see this plan calling for box joints. However I was trying, still ma, to build as planned especially seeing how this is a shop tool cabinet. And yes, I'm using the table saw (SawStop) and my Freud SD208 dado set to make the 1/2" cuts.

I did make a trip yesterday to a woodyard 1.5 hours away in Culpeper, Va (C P Johnson) and bought some wide quartersawn poplar to use for the sides/top/bottom. My concern about less wide boards is I haven't made any cauls yet for gluing up boards yet so I wanted to get the flattest wood I could. This quartersawn could easily just be planed and skip the jointer. Of course I need to do the edges but I mean this is square evensome flat wood. I need to plan don the 4/4 to 3/4" but I expect that anyway.

I'll experiment with the ply some but will get busy prepping this poplar for use.

Thanks for the advice, especially the blades and glue. I'll make sure the blades are clean and sharp.

Last edited by sreilly; 07-08-2018 at 07:10 AM.
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post #10 of 35 (permalink) Old 07-08-2018, 10:40 AM
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Quote:
Originally Posted by sreilly View Post
For some reason I called them finger joints when indeed they are box joints.
Actually the most common term for box joints is finger joints. The reason being when you lace your fingers together that's what it looks like. If you do a google search for finger joints most of the examples will show that joint. Old masters and some of the new ones too call them finger joints. The proper name for the joint Charley mentioned where ends of lumber are joined is a splice joint as that is what it does. The tapered finger's only use is joining lumber together, hence a splice. So when you see the term finger joint don't automatically assume it's not a box joint. I still refer to it as a finger joint because when I lace my fingers together it looks like that joint.

Until all concerned get together and change it, like they did with Pluto's status as a planet to a planetoid, then both terms will get used for the same thing.

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