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Are dovetail joints in pine cabinets important?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mbratch, Feb 23, 2006.

  1. mbratch

    mbratch Member

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    If I were to make a amp cabinet from pine, how critical are dovetail joints to the sound? Is a simpler joint about as good? Or is it more of a structural robustness issue?
     
  2. Barefoot

    Barefoot Senior Member

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    With the inexpensive jigs and routers available today a dovetail joint is a snap. Looks much more complicated than it is. Sure makes a rigid case.

    Is it necessary? I lack the time in grade/time in service to answer.
     
  3. mbratch

    mbratch Member

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    Yeah... the more I think about it... it sounds like a dumb question now. :jo
     
  4. Tinman

    Tinman Member

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    Dovetails have been around far longer than speaker cabs. I can't imagine that they have any advantages in a speaker cabinet other than superior strength. Well cut dovetails will certainly keep a box more rigid over time. Interesting side note; well-executed hand-cut dovetails hold better over time than jig-routed dovetails. Who can tell me why, class. Anyone? Anyone? ........Buehler?
     
  5. Kooper

    Kooper Guest

    It's not a dumb question.You can make accepable cabs with screws and glue if your gonna tolex them anyway.If you drill and counter sink the screws (4 or so along each joint) glue them befor ya screw -em (I like Gorilla Glue) fill the holes with wood filler sand-em up nice.The wood will break before the joint does.The baffel and back panels will keep it from racking,a finger jointed cab would rack witout the panels.I know it sounds like blasphmy to a cab guy but it does work..
     
  6. brad347

    brad347 Member

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    supposedly the more rigid joints allow less unpleasant rattles and vibrations at high volumes. That's the main argument for them I think. I do know that my two blackface fender amps (dovetailed joints) don't rattle at all when cranked and I used to have a '75 super as a teenager (no dovetail) that rattled like crazy (annoying as hell) so maybe there's some truth to it.
     
  7. SteveStrat

    SteveStrat Member

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    The concept with the dovetail and the more simplified finger joint is that there is just more surface area for the two pieces of wood to be glued together than with a regular butt joint. More area at a joint = stronger joint. That's really all there is to it.

    When I make my cabinets I butt joint them then use 3d nails then counter sink them and I haven't had one problem. That doesn't mean that I wouldn't some day love to have a a full 3/4" dovetail gig just for braggin rights.

    Steve
     
  8. RL in Fla

    RL in Fla Member

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    Fenders were box-jointed , not dovetailed , btw . Dovetails have angles . What Kooper says is true to a degree , but a box-joint has about 3 times the surface area (wood and glue) that the same butt-joint has , due to the U -shape of the cuts . (Steve beat me to it) . You also get into the lack of strength gluing end-grain wood , boxjointed gives you cross-grain on both pieces . That's why dados or half-laps are used , even in regular cabinetry with plywood . If it rattles or vibrates other than the backs or front baffles it's a POS however it was made .

    Another butt-joint method is glue it (with 16ga.finishing nails/nailgun to tack it and keep it from slipping & sliding) and clamp it , and drill 1/4" holes afterward and then dowel/glue the holes if you aren't going to tolex it . Countersink the finish nails , hit the dimples with Elmer's filler , drive on to sealer & finish .

    Half-blind dovetails (mostly what you see advertised as dovetails ) came about when routers appeared , as a way to keep drawer fronts from pulling off of drawers over time without a. showing the other (square) half of the dovetail in the front (or in our case , the top of the cab ) , or b. facing the drawer with veneer or an entire second front .
     
  9. Damon

    Damon Member

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    Is it because the bit always leaves one edge semicircular?

    I don't have a router (or a shop to rout in), so here's the modified dovetail I use:

    [​IMG]

    Hand cut and filed big-ass dovetails, all holes and gaps filled with a compound of cabinet-maker's glue mixed with fine sawdust from the palm sander's filter, then added perpendicular piloted countersunk screws. It doesn't look as clean as templated dovetails but it's STRONG. The pic above is one of a set of crates I built for my vinyl. I built a 2x12 with this method (slightly smaller dovetails with one screw per, and mitred cleats for the baffle and back panel), it's light and very resonant. Lotta time and effort though. I want to tolex it soon!
     
  10. donnyjaguar

    donnyjaguar Member

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    Hey Damon, nice work on the wood. My cabinetry is crude by the standards of some of you cats but I have no buzzing or vibrations in my practic amp build. The build-cost of mine was zero. Its made from crates that my friend's company gets their raw materials from Russia in. The amplifier is frighteningly loud. You can see some recent pictures here: ftp://ben_nevis:ben_nevis@206.210.107.171/
    I had to laugh when I saw the Robertson screws. You must be in Canada like me.

    D-J
     
  11. tonezoneonline

    tonezoneonline Member

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    Half blind dovetails were used hundreds of years before routers were around.They can be cut by hand just as well as full dovetails.It just takes a bit longer.
    IMHO all of this talk of joints and tone is fairly mute when your going to cover the wood with glue and tolex.
    As far as structural integrety dovetails and box joints have always been suerior because of the added glue surface.Dovetails are also more of a mechanical joint and that's why I use them over box joints.
     
  12. SteveStrat

    SteveStrat Member

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    I did forget to say that I first glue the joints, THEN I nail them together. After the glue is dry, the nails effect on the strength of the joint is very small. Nailed butt joints are pretty weak.

    Nice looking work RL. Where did you get your finger joint jig, or did you just make one?

    Steve
     
  13. Tinman

    Tinman Member

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    True!

    Well-executed hand cut dovetails hold better than machine-cut dovetails over time because...
    Those router bits are working really hard hogging out all of that wood. After cutting just a few pins or tails, even a brand new carbide-tipped bit is going to lose some of its edge. It will still cut, but as its cutting, its also burnishing the glue surfaces. That is the result of the wood getting smacked with a red-hot, less than razor sharp cutter rotating at blazing speeds. A burnished surface does not take glue quite as well as a hand cut surface, whether that hand-cut surface was cut off the saw, or chiseled.

    That being said, the difference in strength is minimal, and I'm starting to realize that what I'm really doing is showing off my vast knowledge of woodworking.:jo
     
  14. John Phillips

    John Phillips Member

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    The other reason dovetails or box joins are much stronger than butt or half-lap is that the extra glued surfaces are only subjected to shear stresses no matter which way the joint is bent - ie the glue simply has to prevent surfaces from sliding past each other. All glues are strongest used like this. In a butt or half-lap, depending on which way the force is applied, the glue can be subject to 'peel' stress - ie one edge trying to lift first. All glues are weakest like this. All the traditional woodworking joints intended for use with glue are designed to transfer the load into pure shear stress wherever possible. Most pre-industrial glues were not really very strong, but they're almost all as strong as the wood when used like that. See, I did learn something useful in woodwork at school :).
     
  15. jzucker

    jzucker Supporting Member

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    Not sure I agree with that. Screw holes into edge grain is not as sturdy a joint and more prone to separating and racking than finger jointed and certainly no comparison to dovetails though I think dovetails in pine is a bit overkill...

    Incidentally, I hate gorilla glue. Since it foams, folks sometimes use it to cover up bad joinery. It comes apart very easily and IMO, does not produce as strong a joint as yellow glues. However, glues into end grain work poorly which is the whole point of finger and dovetail joints...
     
  16. Tinman

    Tinman Member

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    You lernt well. The other problem with butt or half-lap or rabet joints is that there are no long grain to long grain glue surfaces. In those joints, all glue surfaces have to be long grain to end grain. End grain to anything is a weak joint. That's why you have to use screws or nails on those joints, because the glue ain't doin all that much.
     
  17. jzucker

    jzucker Supporting Member

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    If you don't have a router and/or are not adept at hand cutting finger or dovetails, biscuits is probably the next best way to go and is very easy.
     
  18. Damon

    Damon Member

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    Thanks, bro - frighteningly loud I believe you, look at those trannies and that speaker!

    Robertsons are great screws, eh? Shame they haven't caught on more around the world.
     
  19. RL in Fla

    RL in Fla Member

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    true , but not in their present "round-backed" state as produced by routers and jigs .

    [​IMG]

    Beautiful cabs btw Mike , what's that behind the "woodie" in the first pic ? Looks like an organ .

    I've got several jigs Steve , the one I use on the router table for boxes/thru dovetails is made using a Stots template maker ,
    the ones for a handheld router are templates for a Hartville Tools (identical to a Porter-Cable).

    Any properly glued , reasonably "helped" (with nails , screws/dowels, biscuits) joint is gonna take a hell of a beating once it's together and tolexed . Here's some joints in a pine Champ cab from around '70 ......

    [​IMG]

    [​IMG]

    [​IMG]

    Even though they're abysmal , gaps on all 4 joints , patched with filler (the white stuff showing) , and glued with "pre-high-tech" glue , it's still sturdy even with no tolex "matrix" to help . ;) Up to about a 2x10 size they're probably "all good" unless they're really getting slammed or G. O.-rilla'd .
     
  20. tonezoneonline

    tonezoneonline Member

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    Thanks for the kind words RL.That's actually a pulpit behind the amp.My shop is in an old church built back in 1894.
    Yea,everything kind of went wild since the introduction of the router.How could we live without them?
     

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