Festool Domino question

[Zeddedhed]

Just a quickie this.... (although I'm sure it will spark a debate!!)

If using Dominos to connect carcass elements (legs to stretchers/rails) is it necessary to glue the faces of the timber (one end grain, one long grain) as well as gluing the Dominos, or am I wasting glue? Is it enough to just glue the dominos into both elements?

Glue in question will be Titebond III

 

[custard]

It's enough to glue the dominos, but Festool's tests showed the joint was 30% stronger when you glued both the tenon and the mortice.

If I'm using UF glues like Cascamite or Bordens (as I normally do with dominos in order to have loads of time to ensure everything is absolutely square and all shoulders are tight) then I do apply glue to the end grain because UF, like epoxy, does give strength with end grain gluing.

 

[Zeddedhed]

It's enough to glue the dominos, but Festool's tests showed the joint was 30% stronger when you glued both the tenon and the mortice.

If I'm using UF glues like Cascamite or Bordens (as I normally do with dominos in order to have loads of time to ensure everything is absolutely square and all shoulders are tight) then I do apply glue to the end grain because UF, like epoxy, does give strength with end grain gluing.

Thanks Custard. Do you have a link to the Festool test info?

 

[Random Orbital Bob]

I always glue all mating surfaces purely from a "it makes common sense to me" line of thinking and nowt anywhere near as scientific as Custards response.

 

[pcb1962]

Thanks Custard. Do you have a link to the Festool test info?

Not a Festool video but this one has quite a lot of info: https://www.youtube.com/watch?v=e_gc64MlYzE

 

[custard]

Do you have a link to the Festool test info?

I'll have a hunt around for it tonight, I seem to think it was some work done by Festool USA and quoted in Fine Woodworking when the Domino was first launched in the US.

 

[custard]

I'm looking but so far without success. However, this video discusses the question and comes to the same conclusion, glue on both the mortice and the tenon is way stronger,

http://www.halfinchshy.com/2012/04/domi ... -glue.html

The problem is that with PVA there may not be enough time to glue both the mortice and the domino, and then get the piece cramped up, especially with Titebond which is especially "grabby". Personally that's why I use Cascamite or a UF glue, I want 30 or 40 minutes of relaxed open time to get everything dead right, even if that means the workpiece then has to to spend 12 or more hours cramped up.

Rick Christopherson (who wrote the Supplementary Domino Manual) also advocates gluing both the mortice and the domino, but he acknowledges that in some commercial applications reducing time in cramp is worth sacrificing joint strength for, in this case he makes the clever observation that you're better off just gluing the domino rather than just gluing the mortice, as the small grooves on the face of the domino will at least distribute the glue a bit more evenly throughout the joint. If I'm making a jig, and just using the domino as a location device, then that's what I do, PVA just on the domino, but for a piece of furniture that I'm going to sign my name to, then it's a slow setting UF glue applied to both.