Mortise & Tenon joinery on wide boards

[TonyV]

I've designed & plan to build a coffee table to replace the beat-up POS we have in our family room. The wife & I bought that about 15 years ago before we had kids. To say it's seen better days is an understatement.

The new table needs to have 4 drawers in it. As a result, the sides are going to be about 13.5" wide & have 4 drawer openings in them. I'll make the openings by ripping the boards for the sides into 5 pieces, then cross cut the drawer faces out of 2 of the pieces, then glue the other parts back together in the right order / places.

I intent to join the sides to the 2" square leg posts using mortise & tenon joinery. I've designed 3 tenons on each end, each 3" wide & an inch long, with corresponding mortises in the legs.

My question is: what effect will wood movement have? Should I:

• Cut the middle & bottom mortises longer than the tenons are wide
  
• Cut slots in the middle & bottom tenons for a peg to pass through
  
• Drill holes for dowel pegs through the inside of the legs
  
• Glue the top tenon only
  

This will let the sides expand & contract up & down as they please.

I'm going to make & install frames between the drawers using dadoes cut in all 4 sides. If I join all 4 sides to the 4 legs the same way, then the whole assembly ought to move together & the project shouldn't break itself apart. Right?

Thanks for any ideas.

Tony

[FC27*]

Hi Tony,

I'll let others with more knowledge provide advise on the tenons. The only thing I would recommend, especially if young ones are around, is to consider the risk of someone getting their fingers pinched or worse by someone pulling on a drawer from the opposite side.

Fred

[ztifpatrick]

I've designed & plan to build a coffee table to replace the beat-up POS we have in our family room. The wife & I bought that about 15 years ago before we had kids. To say it's seen better days is an understatement.

The new table needs to have 4 drawers in it. As a result, the sides are going to be about 13.5" wide & have 4 drawer openings in them. I'll make the openings by ripping the boards for the sides into 5 pieces, then cross cut the drawer faces out of 2 of the pieces, then glue the other parts back together in the right order / places.

I intent to join the sides to the 2" square leg posts using mortise & tenon joinery. I've designed 3 tenons on each end, each 3" wide & an inch long, with corresponding mortises in the legs.

My question is: what effect will wood movement have? Should I:

• Cut the middle & bottom mortises longer than the tenons are wide
  
• Cut slots in the middle & bottom tenons for a peg to pass through
  
• Drill holes for dowel pegs through the inside of the legs
  
• Glue the top tenon only
  

This will let the sides expand & contract up & down as they please.

I'm going to make & install frames between the drawers using dadoes cut in all 4 sides. If I join all 4 sides to the 4 legs the same way, then the whole assembly ought to move together & the project shouldn't break itself apart. Right?

Thanks for any ideas.

Tony

I'd be interested to hear what others say, but I'd;

[*]Glue the top tenon only AND

[*]Cut the middle & bottom mortises wider than the tenons are wide AND

[*]Cut slots in the middle & bottom tenons for a peg to pass through.

This way the movement is downward away from the top and the other tenons are secured with pegs in elongated slots with no glue.

I have not enough experience with drawers to say anything on that.

I like the way your creating your drawer fronts, should be nice flowing grain.

Good luck

[PaulMarcel]

+1 to everything Chris F said. Just to expand on the reason to glue the top tenon is that you will lock it in place and let the others float. You could peg them from inside if you don't want the pegs to show. The idea of gluing your reference tenon comes up with a breadboard end; there you glue the middle tenon so the expansion/contraction is split between the two edges.

[TonyV]

I'd be interested to hear what others say, but I'd;

[*]Glue the top tenon only AND

[*]Cut the middle & bottom mortises wider than the tenons are wide AND

[*]Cut slots in the middle & bottom tenons for a peg to pass through.

This way the movement is downward away from the top and the other tenons are secured with pegs in elongated slots with no glue.

I have not enough experience with drawers to say anything on that.

I like the way your creating your drawer fronts, should be nice flowing grain.

Good luck

Well, actually, when I listed everyting with bullet points, I meant to do all of those things in that order, not an either or choice. I thought I had clicked on the numbering button. Guess my eyes aren't resolving as well as they used to as when I look closer to the screen now, I see that I did click on the bullet point & not the numbering button. Oh well.

As for the drawers & fingers, my kids are 13 & 11. I think they're old enough to know better. But if one is dumb enough to reach inside the table, grab the drawer pull, and yank it while their sibling is rummaging in the other end, we'll make that kid take a turn & see how it feels.

Now I just gotta figure out how much bigger to make the mortises than the tenons.

Thanks everyone.

Tony

[TonyV]

I just plugged some numbers into the Shrinkulator. The wood is red oak from Florida. I assume it's Southern Red oak, but I tried both Southern & Northern red oak. I used the minimum & maximum humidity from this site.

The shrinkulator says that the Northern red oak will move 0.12" radially and 0.27" tangentially; the Southern red oak will move 0.15" radially and 0.37" tangentially. This stock is quarter sawn, so its movement across its width will lie more in the radial direction than the tangential direction. That means its width will change by about 5/32" over the course of a year here in the NYC metropolitan area.

So what I'm going to do is make the middle & bottom mortises 3/16" longer than the width of the tenons. That should be more than enough room to accomodate the movement of the sides over the years.

Thanks

Tony