Dado Fitment

[Michael Thuman]

I am to groove a solid woood assembly for 3/4" plywood that is actually around .722 to .725.

I have found that in Mortise and Tenon joints I alwasy size the tenon .01 smaller than the mortise to allow gule to set up in the joint properly and not get squeezed out.

 

Now comes the dadio joint.  If I create the joint a .730 am I defeating my self? 

That would be +.008 to + .005.  Still quite tight fit but is that enough to allow the glue to properly work?

Also this is a cross grain joint on veneer plywood.  The long grain is 90Deg to each other.  Plywood being stable Should I be concerned with expansion and contraction.

 

In the past I set the dadio tight or .725 or 0.000 to .003 loose.  That once pounded in squezzed out some glue but has held for years.  However that was a plywood to plywood joint.

I doubt you could ever see .005 to .008 gap at the intersection but it will be glue tight to the top of the groove.

Leaving a little wiggle room on the bottom (hidden).

 

Does the fact that plywood into solid wood change anything?

 

 

 

[John Morris]

Michael I have fitted ply to solid and solid to ply just as you are suggesting, I actually believe that the tighter the fit the better with dados. The glue can squeeze out all it wants, the real adhesion comes when the wood fibers and glue mix, and are compressed onto each other. Purposefully leaving a gap so the "glue will work" is in error IMHO. That would only weaken a joint, you need the wood to wood compression in order to properly have the "weld" for both pieces of wood to become one. For much of my work I tighten down my clamps well, till they bend nearly, and I look for maximum glue squeeze out, I like to see the glue pour out of my joints. The remaining glue is being forced into the wood, and the fibers are bonding.

 

I would join your ply's and solids with reckless abandon, with dados, you really don't need to be concerned with expansion and contraction as dados are typically cut perpendicular to the grain expanding. Hope I made sense.

 

 

[Michael Thuman]

Well given the advice the dadio kit i have is 23/32 or .718 and the plywood coming in at .719 to .730 I think I will cut it at .718 and see if I can press it in.  (Test Peice Number one).  If use some shims to slowly creep up on a press fit with wood damage.  I will let  you know what I come up with.

[Michael Thuman]

23/32" too tight 23/32" +1 shim just right.