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  • biscuits VS mortise and tenons

    I have taken a few woodworking courses from the local college now, and there is a lot of inconsistency with the information regarding biscuits and biscuit joiners.

    I have had one cabinet making instructor tell me that biscuits are only for alignment and provide no structural strength.

    I have had a different cabinet making instrutor tell me that a bicuit joint is incredibly strong, as the glue swells the biscuit and forms a strong connection (and there is more surface area for the glue). He said a double biscuit joint is as strong/stronger then a well made mortise and tenon.

    What do you guys think?

  • #2
    Re: biscuits VS mortise and tenons

    Everything I've read and been told says biscuits add strength to the joint for the same reason you mentioned. My experience says the same. They're also easier to do than cutting mortise and tenon. Why go thru all the trouble to cut slots and slide in biscuits if just for alignment? Seems there are other, easier methods for that. This is an interesting subject. I wonder what others think?
    If at first you don't succeed, try reading the owners manual.

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    • #3
      Re: biscuits VS mortise and tenons

      Biscuits add strength because of the different grain directions that joins the wood pieces together. If all the grain went the same way, as in gluing like grains together edge to edge, it would fail faster than having the multi direction grain of the biscuit in the joint too. Granted, gluing up wavy boards with biscuits is a great way to line them up, but that is only part of the purpose.

      Mark

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      • #4
        Re: biscuits VS mortise and tenons

        A couple of months ago Wood Magazine tested various joints under stress. M&T was the strongest, but biscuits did add strength. It was a real good article.

        It was the Nov 2006 issue.

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        • #5
          Re: biscuits VS mortise and tenons

          FP I agree with instructor #2

          I also think it depends on where you use the biscuits... for instance myself personaly I would never use biscuits to join aprons to legs for example.
          However for me biscuits have completely replaced dowels for edge gluing panels together.
          Cheers! - Jim
          -------------
          All truth passes through three stages: First it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident. - Schopenhauer

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          • #6
            Re: biscuits VS mortise and tenons

            Norm says biscuits add strength......Nuff said!

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            • #7
              Re: biscuits VS mortise and tenons

              I tend to agree with Instructor #1 but I can also see some validity in Instructor #2 point of view. A properly glued joint is technically stronger than the wood itself is. So under stress, the wood should fail before the properly glued joint would. Now if the joint is not properly prepared and fails than a biscuit may slightly increase the amount of stress needed for the improperly prepared joint to fail.
              Teach your kids about taxes..........eat 30 percent of their ice cream.

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              • #8
                Re: biscuits VS mortise and tenons

                Originally posted by franklin pug View Post
                I have taken a few woodworking courses from the local college now, and there is a lot of inconsistency with the information regarding biscuits and biscuit joiners.

                I have had one cabinet making instructor tell me that biscuits are only for alignment and provide no structural strength.

                I have had a different cabinet making instrutor tell me that a bicuit joint is incredibly strong, as the glue swells the biscuit and forms a strong connection (and there is more surface area for the glue). He said a double biscuit joint is as strong/stronger then a well made mortise and tenon.

                What do you guys think?
                First a properly glued joint will be stronger than surrounding wood. Many many tests have proven this.

                By nature of changing grain direction biscuits do add strenght but their prime function is alignment.

                I days past with different glues things like dowels, mortise and tendons and splines and such were used to add in alignment but also to add strenght. But with today's glue they are primarily for alignment.

                Interestingly Festool has come out with the Domino, it is a tool that makes floating or loose mortise and tendon joints. It cuts a slot into which the domino or loose tendon is inserted. The domino is much thicker than a biscuit so if you looking for strenght this is the winner hands down.

                Careful with biscuits, if you notice Norm is using them less and less. As the biscuit swells if if is too close to the surface it will telegraph it's shape to the surface.

                Again all the tests have proven modern glues are more than sufficient to join wood together without any need to additional strenghtening.
                Rev Ed

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