Festool Owners Group

FESTOOL DISCUSSIONS => Ask Festool => Topic started by: goodwood on January 25, 2020, 11:34 PM

Title: Edge Joining with domino
Post by: goodwood on January 25, 2020, 11:34 PM
Has there been any study regarding deflection on edge joined boards?  When designing a shelf unit recently I was using sagulator to project the amount of sag that would occur with 1 inch thick shelves 36 inches long by 11 1/4 wide. The wood is african mahogany.  The shelf will be supported by medal paddle supports  - 2 on each end and ??? across the back (that's what I was trying to determine).  Sagulator does not address that but does anticipate using a lip.  Based on sagulator the expected weight should be supported adequately but what if I am wrong about the weight to be supported?  So then I got thinking about the fact that I typically make shelves out of three pieces edge joined together using dominos.  Would that not make the shelf piece more rigid and less likely to sag than a shelf made of one piece of wood the same size?   Does anyone know of any fact based guidelines for this?

Thanks in advance
Title: Re: Edge Joining with domino
Post by: tjbnwi on January 26, 2020, 12:05 AM
I do not think the edge joining has any affect in this scenario. You have not increased the thickness of the material.

Title: Re: Edge Joining with domino
Post by: ChuckS on January 26, 2020, 12:28 AM
Not sure if this American Woodworker article is helpful to you: https://www.popularwoodworking.com/projects/aw-extra-3614-stronger-shelves/

There is nothing that can provide more rigidity to a shelving than a vertical support in the middle. One way to hide the centre support, in the case of a bookcase, is to glue a bookspine to the front edge of the support so the support looks like a book on the shelf (the support is trimmed narrower to accommodate the spine). In the credenza shown below, the dadoed centre support is hidden behind the sliding doors.