Is one-way breadboard movement possible?

[Dsrekab]

Hello everyone!  I am in the planning stages of a top with two 20” wide planks so I’m thinking of doing breadboard ends to help with movement.  I’m curious if it’s possible to force all the movement in the panels toward one side of the breadboard, so that the front is always flush.

I was thinking of doing what would traditionally be the center drawbore hole and mortise on one side, then making the elongated drawbore holes and mortises progressively wider as I move toward the back of the top.  Maybe waxing the haunch as well to help things slide.

Do you all think it’s possible or is that too movement?

Thanks in advance

 

[wtnhighlander]

What you describe is just how I would go about directing the movement to one side. I think only the drawbore hole nearest the non-moving edge needs to be round, and you might even use glue in that area. The other holes in the tongue can be slotted equally to the longest, progression is not really necessary.

Having said that, I might add that a batten under the top, oriented with its width perpendicular to the top thickness, and being somewhat wider than the top is thick, should be much more rigid aganst cupping of the wide boards of the top. You can also use a breadboard that is thicker than the top to gain stiffness, and offset the mortise to make the top surface flush. How much rigidity you need depends on the species and cut of the top planks, but at 20" wide, I'm betting they are plain / flat sawn, the cut where cupping is most common.

[Mark J]

I suspect you went to some trouble to find 20" wide boards, but have you considered using thinner boards (or ripping the 20" boards)?

[gee-dub]

I do this all the time with 'against the wall' items.  Fixing one end and floating toward the back keeps the front elevations consistent throughout the year.

Example 1.

Example 2.

The spline / plug is not necessary.  It is just a decorative element I use.  The ends of your breadboards would be closed like usual.  There would be room for expansion at one end which is how these pieces are made.

If you look closely in the next pic you can see that the dowel holes (I pin from underneath) are round at the front, slightly long in the middle and longer at the rear.

The front of the breadboard is set back to accept the spline.  The rear moves in and out of the breadboard slot.  In your case the tongue would be captured with room at one end for movement.