Backs and Bottoms - tongue and groove vs. shiplap

[Jeff Ranck]

So in the course of designing a thread cabinet for my wife, I decided to use beaded shiplap for the back/front. However, as I was looking at other builds, I notice sometimes that tongue and groove is also used for the backs of cabinets, hutches, etc., the bottoms of chests (like a traditional tool chest) and so forth. This got me thinking about the question of when to use a shiplap and when to use tongue and groove.

Are there any tradeoffs that should be taken into account? Is it simply a design choice? Shiplap for thinner boards, tongue and groove for thicker? I had never thought of it nor read anything about when to use one vs. when to use another.

So what should I be thinking about when choosing?

[Prashun Patel]

Tongue in groove keeps pieces in the same plane. If you don't fear warping then a ship lap will work.

Also on a thin back, you may not have enough thickness to make serviceable tongues and grooves.

Shiplaps are quicker to produce (for me)

[William Fretwell]

The joints have different properties. A chest bottom in a tongue & groove joint allows for wood movement of the chest sides, the joint creates the mechanical integrity to hold the bottom. A ship lapped bottom requires additional mechanical support but can give a bottom flush with the bottom edge of the sides more easily and may be easier in small boxes. A chest made of plywood will be dimensionally stable and accommodate a ship lapped bottom better than tongue & groove.

Overall the mechanical integrity of the tongue & groove should indicate when it is required. As a simple vertical cladding shiplap will dry more easily, is easier to make and so less expensive.

[glenn bradley]

Prashun took the words out of my mouth. If the scale of the piece will support back slats of say, 1/2" thickness I will use tongue and groove. As things get thinner you have to again look at scale; how long are the slats? Will an 1/8" T&G do anything for me or will it split since it is so thin and too long a run?

T&G or ship lap, my back slats generally fit into to a groove at the bottom. sometimes also at the top. The top groove is deep enough to slide the slat up into, swing the bottom over the bottom groove and drop it in. As stated, the joinery along the run varies with scale.

369570

[ken hatch]

I have to add one more thing in addition to thickness it kinda depends on tools at hand:). Not everyone has a match plane to make the tongue and groove easy. .

ken

[glenn bradley]

I have to add one more thing in addition to thickness it kinda depends on tools at hand:). Not everyone has a match plane to make the tongue and groove easy. .

ken

Tablesaw :).

[steven c newman]

While watching Ishitani build a cabinet....he made a series of thin boards (~1/2"?) with a groove on each edge. He then slid a thinner piece into the grooves where each pair of grooves met. Almost like a loose tenon? No glue was used.

[Jeff Ranck]

a loose tongue. Interesting. Never thought of that one.

[Jeff Ranck]

I was planning on having the back be about 1/2", so maybe I ought to rethink the shiplap and repack it with a tongue and groove. Of course, then I have to buy the Lie-Nielson 49 to make it.

[steven c newman]

Note: The slats also sit in a groove at the top and bottom of the case, and along the sides.

He was making a cabinet from a Ginkgo Tree that was made into a HUGE table top. He had it resawn down to make all the parts. The handles were shop made from brass...

[Rick Malakoff]

Wouldn't a loose tongue be a spline?
Rick

[Jim Koepke]

Wouldn't a loose tongue be a spline?
Rick

There are many things the same called by a different name. To confuse things even more, consider that often things differ yet share a name.

The world is a confusing place. Somedays it makes me want to lie down and take a nap.

jtk

[Jeff Ranck]

The world is a confusing place. Somedays it makes me want to lie down and take a nap.

jtk

Best idea I've heard all day.

[Frank Drew]

In this application, I think spline is more correct than tenon.

I like solid bottoms for chests, but shiplapping boards for the back is fine, IMO. In any case, for either t & g or shiplap, allowance has to be made for wood expansion.

[Bruce Page]

I use T&G if the board length and thickness allow it. I also like the look of a small edge radius. The boards on this back panel are ½ X 39”. I’m not a Neander so this was done on the TS & router table.

[Patrick Chase]

Wouldn't a loose tongue be a spline?
Rick

Indeed. I was about to post and say the same when I saw your post.