neoOberon

Plywood Box Joinery

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I'm doing the ground work for building plywood boxes (cabinetry and bookcases). I'm was intending to use rabbits for the joinery...

 

However this just caught my eye...maybe this is the way to go. It's labeled a finger joint, but not what I would typically call a finger joint (I'm new, what do I know?).

 

mirrorboxjointassembly.jpg

 

Just wondering what other people use...is there a consensus on what joint is best for my application. 

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I've used this before on drawer construction and find it to work well and easy to cut.

 

What did you use to cut it? Dado stack or a router? (both?)

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   For basic cabinet construction, that's a good joint, and holds up very well.  A dado set up is the easiest for cabinets... Do all like cuts at once, then reset the dado, and make your finish cuts....  Always test before doing the final cuts on scrap to be sure you've got it right.

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I'm doing something very similar on my cabinets. I'm using these router bits for it. I think the new made in USA set is made by Whiteside. The joint is tight and strong. 

 

http://sommerfeldtools.com/3-pc-tongue-groove-cabinetmaking-set

 

http://sommerfeldtools.com/professional-equipment-and-tools/router-bits-and-sets/tongue-groove-set-usa

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There is a reason for that style of joint on boxes. Its good for end panels where your FF is flush cut but those are usually just stand alone boxes. The main reason is the plywood itself and it doesn't do any good or make things any easier unless you use the right cutter configuration. The joint is made to address the problem on inconsistant plywood thickness which causes grief with full dado's. If you don't cut above the tongue your wasting your time and just following the inconsistent thickness. The joint was made early on for cnc and panel router use.

For example if you were using a dodo blade the cut is made with the panel on end being run between the blade and fence (tongue side against fence), not safe and no way to push out any bow safely so don't do that. 

With a router the tonge side goes to the table and a cutter is raised tongue thickness above the table. Panel is pushed under the cutter keeping constant pressure down on the table to push out any bow.

With a shaper you can go either direction to suit your needs. Vertical with nickers or flat above with a shear cutter. Either way with a power feed to push out any bow.

With a cnc you are obviously above so the cutter is set at tongue thickness above 0 and that is of course the table not down from the top of the panel.

 

Again if your not using the right cutter configuration your defeating the purpose.

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 The joint is made to address the problem on inconsistant plywood thickness which causes grief with full dado's. If you don't cut above the tongue your wasting your time and just following the inconsistent thickness.    For example if you were using a dodo blade the cut is made with the panel on end being run between the blade and fence (tongue side against fence), not safe and no way to push out any bow safely so don't do that. 

 

PB - I'm trying to wrap my head around that.  I get the inconsistent thickness problem, and why it causes headaches with dado grooves,.

 

I'm trying to understand why the board would need to be on edge.  Is the issue here, that if you cut the rabbet on the TS/dado blade with the ply's face on the table, your rabbet will follow a potentially inconsistent reference surface?

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PB - I'm trying to wrap my head around that.  I get the inconsistent thickness problem, and why it causes headaches with dado grooves,.

 

I'm trying to understand why the board would need to be on edge.  Is the issue here, that if you cut the rabbet on the TS/dado blade with the ply's face on the table, your rabbet will follow a potentially inconsistent reference surface?

 

Yes a 3/8x3/4 rabbet is just that 3/8x3/4. Lets go to some extremes so its easy to picture. Assume you had a sheet of ply that was 18mm in some spots and 25mm in others. The saw blade is elevated 8mm the remaining tongue in some spots would be 10mm and others would be 17mm. 

Now change that up and run the sheet on end between the blade and fence. We can use just any wide stack size and elevate the cutter to 3/4 and move the fence 8mm away from the blade. The blade is going to remove 10mm in some spots and 17 in other spots resulting in a 8mm tongue the full length of the panel irregardless of the thickness. 

 

Its all about where you reference your cutter. This applies to all woodworking not just sheet goods.

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Yes a 3/8x3/4 rabbet is just that 3/8x3/4. Lets go to some extremes so its easy to picture. Assume you had a sheet of ply that was 18mm in some spots and 25mm in others. The saw blade is elevated 8mm the remaining tongue in some spots would be 10mm and others would be 17mm. 

Now change that up and run the sheet on end between the blade and fence. We can use just any wide stack size and elevate the cutter to 3/4 and move the fence 8mm away from the blade. The blade is going to remove 10mm in some spots and 17 in other spots resulting in a 8mm tongue the full length of the panel irregardless of the thickness. 

 

Its all about where you reference your cutter. This applies to all woodworking not just sheet goods.

The tongue is manufactured precisely by the gap left between the blade and fence, rather than what is left above the blade. So blade height is irrelevant when it comes to tongue thickness.

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The tongue is manufactured precisely by the gap left between the blade and fence, rather than what is left above the blade. So blade height is irrelevant when it comes to tongue thickness.

 

Exactly which is why you reference your cutter in most every part of woodworking. Something as simple as a tenon is more of a pain if you don't reference your cutter to the face. But I will say the above was just an example don't make a cut like that on the tablesaw its not safe nor will it actually work if you have any warp. That system is designed to be used with power fed option where your hands can be in your pockets not right at the cutter. I have never tried it but I assume you could go under a router bit but the results may be ugly and you would have to keep it tight to the table.

 

The sommerfeld method i think uses an actual tongue and groove cutting both sides with a net result being the distance between two cutters. You see this method more in home shops mainly because its not productive and most don't own cnc's or shapers. I really see it more as a gimmick to sell tools. Standard full width dado's are usually just fine and only need slight sanding with a ro sander. The only reason for a home shop to worry about either method is if you were to use prefinished material like prefinish ply or cabinet liner.

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I'm still not getting the ah-hah that Vinny has experienced...    Stealing PB's response in another thread since it's more relevant here:

 

Sommerfeld is more of a traveling show type sales company. The CMT set can be had for a few bucks less even comes with the pretty box. Really with todays tools they are more of a gimmick than anything else. A Freud t&g set will produce the same results if you must use this gimmicky method of assembly.

 

So you consider the T&G gimmicky?   You mentioned full-width dadoes up above?   Do you mean like cutting a 1/2" dado and then taking a 3/4" piece of ply and cutting a rabbet to leave a 1/2" tongue (with all of the particulars of inconsistent thickness and bowing accounted for)?   Is that somehow better that what the T&G bit sets produce?   I see how inconsistent thickness or bowing can cause you problems if you are doing a rabbet, but I guess I don't see why it's a gimmick to eliminate that problem with two cutters like the router bit sets do?

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I'm still not getting the ah-hah that Vinny has experienced...    Stealing PB's response in another thread since it's more relevant here:

 

 

So you consider the T&G gimmicky?   You mentioned full-width dadoes up above?   Do you mean like cutting a 1/2" dado and then taking a 3/4" piece of ply and cutting a rabbet to leave a 1/2" tongue (with all of the particulars of inconsistent thickness and bowing accounted for)?   Is that somehow better that what the T&G bit sets produce?   I see how inconsistent thickness or bowing can cause you problems if you are doing a rabbet, but I guess I don't see why it's a gimmick to eliminate that problem with two cutters like the router bit sets do?

 

Its a gimmick because they make it sound like its something special without a explanation as to why its even used, the why is the magic show but once you understand the why all your woodworking gets easier.. Any t&G bit set will do exactly the same thing without the Somerfeld name for less money. No a full width dado is a 18mm dado to fit the full thickness of 18mm plywood. Now the ply may have high spots making the joint a little tight in some spots but nothing a sander wont fix easily. Just a plane old every day dado joint. If you think about it you have a similar issue with most any WW joints you just have to think about why, and understand the cutter and machine. 

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Its a gimmick because they make it sound like its something special without a explanation as to why its even used, the why is the magic show but once you understand the why all your woodworking gets easier.. Any t&G bit set will do exactly the same thing without the Somerfeld name for less money. 

 

I'll agree that Marc Sommerfeld is somewhat overhyping his bit sets, and he's a bit of a goober. The only thing he can claim is "innovative" is height matching the bits, which isn't necessary but does make things easier and quicker for a hobbyist or someone who doesn't have a station for each and every part of the process. I'm willing to bet 99% of the people on this forum, Marc Spagnuolo included aren't geared with production equipment for batching out hundreds of cabinets a week. Each bit set is a system, much like Festool, Tormek, Shopsmith, etc, if you have the bit set, why not get the height setting accessory to make things faster, easier and repeatable. As for the bits, they are well made, they're higher quality than standard run of the mill bits and would put the quality up there with Freud. Originally his bit sets were made by CMT. Are they the be all, end all of router bits? No. Can you arrive at the same end result with 50 different other methods and costs? Of course.

 

It comes down convenience and what tools you have to work with. A router table setup with bits is gonna be cheaper than a basic shaper and cutters, A dado blade on a table saw is gonna be the same thing, cheaper and more versatile use of space for the majority of woodworkers. 

 

The "WHY" is not usually explained because the majority of people and their behavior is "It works that's all I care about" vs why it works. These are the things that separates a craftsman from a DIYer. 

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I'll agree that Marc Sommerfeld is somewhat overhyping his bit sets, and he's a bit of a goober. The only thing he can claim is "innovative" is height matching the bits, 

 

Its really not innovative at all more so common sense. If you think about how these have been cut on a shaper before Sommerfeld was born its really just a matter of moving the cutter up with a spacer. Router bits have been made this way for many decades. If I sell you two cutters made with the same shaft and I take off one cutter and replace it with a spacer you now have a matched set. That in itself is sort of a gimmick because you could just remove the nut and drop on a spacer and cutter yourself just like a shaper.

 

It really has nothing to do with production work or shapers its more about the smoke and mirrors and the why. Once you learn to process the why it by default makes the rest of your woodworking easier on your brain, back and wallet.

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The "WHY" is not usually explained because the majority of people and their behavior is "It works that's all I care about" vs why it works. These are the things that separates a craftsman from a DIYer. 

 

Well said T. 

 

 

Its really not innovative at all more so common sense.

 

I would agree but I think it's like so many tools for the hobbyist...buying convenience/time at a high cost.  Without the experience, knowledge, and tools, it certainly sounds a helluva lot more convenient to just swap between two matched bits in the router table than most other hobbyist-level options.  I know it sounds a lot easier than my current method of doing dado joints by routing the dadoes handheld running along a straight edge clamp...so the marketing certainly works on me. =p

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 Without the experience, knowledge, and tools, it certainly sounds a helluva lot more convenient to just swap between two matched bits in the router table than most other hobbyist-level options.  

 

 

So lets look at just that one point. Can you change the bits in your router table without moving the cutter. I have the Powermatic by Jessem nothing special and it can't be done without a custom bent wrench set or becoming Gumby under the table. Second you should not be bottoming out your bits in the collet one day you will have a rocket bit and hopefully not learn the hard way. This tid bit is in your manual.

 

Remember what Norm said before every show. :)

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That's where rubber O-rings come into play.

 

 

Rubber rings still change the height just enough make you mad. This is why a cnc with a straight cutter runs back to home plate after a tool change even if its the same cutter from the same manufacturer. The o ring will compress differently every time which is exactly what its supposed to do.

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O-rings aren't there to get you consistent heights, it's to prevent you from bottoming out the bit. For consistent heights, setup blocks. They aren't that hard to make, or you can buy them. I'm pretty sure there's at least one or two kits on the market that come with them.

 

But as far as o-rings go, it's really, really close.

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