Splines VS Keys

[thewoodwhisperer]

I'm putting this in the Advanced forum because this is purely an academic question. I'm working on a joinery book and there's some terminology I'd like to get right. I know many of us misuse or don't differentiate between these terms, so I'm hoping you guys might be able to look at some of the print resources you have around and also draw on your own knowledge to confirm what I'm about to put into print. 

Because my print resources actually conflict with one another, it's been hard to nail down definitions that work in all scenarios. So here's what I've boiled it down to and it focuses solely on how the joint was made. 

A key is something that is cut and inserted AFTER the miter joint is glued up.

A spline is something that is cut and inserted DURING the miter joint glueup. 

I initially thought the defining factor would be things like grain direction, shape of the piece being inserted, or length of the insert and its relationship to the length of the joint, but all of these things end up having exceptions. So what I'm hoping you guys can do is find a case where the above "definitions" are not correct. 

Thanks for the help.

For reference, here's a key (only goes part-way through the joint and is added after the miter glueup):

 

And here's a spline (goes all the way across the joint and is added during the miter glueup):

[wtnhighlander]

Personally, I have always interpreted a "spline" as a loose piece with grain parallel to the main piece, and typically having a straight shape.

A "key", on the other hand, has grain running perpendicular to the main pieces, and typically having an interlocking shape.

In other words, an example of a spline would be a loose 'tongue' used to aid in edge-gluing boards to form a panel.

A key would be like a butterfly inlay used across a crack or joint to prevent opening.

In the case of miter joint reinforcement, under my assumed definitions, they could sort of swing either way, but I choose to call flat ones "splines" and dovetailed ones "keys".

[gee-dub]

Quote

 

A key is something that is cut and inserted AFTER the miter joint is glued up.

A spline is something that is cut and inserted DURING the miter joint glueup. 

 

These definitions work for me.  The grain direction is always different for the key of spline versus the mating material if it is to be structural.  Decorative elements are "game on" and get to bend nearly all rules ;-)

Another favorite peeve is dado and groove; two different things used interchangeably.  Planer, thicknesser / jointer, planer . . .  so much can be a matter of semantics.  It is when specific "terms" for things in the vernacular of an area of activity or expertise get tromped that one can come off sounding ill-informed. 

As an author you are under the microscope but, consistency can save your butt.  If a key or spline is consistently called a "spline", your writing and your readers will become one with the behavior and things will read well and (more importantly) convey your message well.  The same holds true if a key is always and specifically a key and a spline is always and specifically a spline but, you get my drift. Party on dude!

[..Kev]

Although I'd be the first to admit that my terminology may not be correct, I've never called either of these a key.  I've always called both a spline, just two different ways of doing the spline.  Now you've got me thinking!

 

[Tpt life]

In motors, spline used to be integral, and keys used to be loose. At some point spline came to be known as an integral key, then spline and key started to be interchanged. Now spline is being called a key, especially an integral key. It is not at all a surprise that this is being discussed, and I doubt you will find consensus. 

[Tmize]

I agree with your definition. The way I have always thought about it it a key is something you use to lock a box or something after it is built. A spline is what I think of as a spine of a book it's installed during the binding portions of making it. 

[Chet]

In Tage Frid's book 1 on Joinery,  he refers to both as splines.  But having said that, I did a resent drawer joint that he had shown in his book.  But when researching on the internet the joint name didn't bring up images of the joint the way he cut it.  I think terminology kind of gets tossed around but the trick would be to stay consistent in you referencing in the book

[thewoodwhisperer]

7 minutes ago, Chet said:

In Tage Frid's book 1 on Joinery,  he refers to both as splines.  But having said that, I did a resent drawer joint that he had shown in his book.  But when researching on the internet the joint name didn't bring up images of the joint the way he cut it.  I think terminology kind of gets tossed around but the trick would be to stay consistent in you referencing in the book

Interesting. I can say that most books I have on joinery, including Tuanton's Complete Illustrated Guide by Rogowski differentiate between them. But it's the notable exceptions that keep me wondering which course I'll take. Thanks for the info on Frid.

[Unknown craftsman]

I've used the one in the first pic it's such a easy way to connect miters. Both can be a challenge to glue up.

Ever since I bought the domino I have not made one. I should keep that in mind one day the domino will probably break down.

Aj

[curlyoak]

Unless the purpose is to line up the joint only and strength is not needed, otherwise I make splines perpendicular on the grain. I also have not made a spline for some time now that I have the domino.

[Llama]

I think a key needs a lock...

What I mean is a key needs to have a shape that interlocks with the other piece.

Flat piece = spline

"dovetail spline" = key 

[..Kev]

Interestingly enough, a Google image search shows both versions being splined miters.  I certainly don't consider that definitive evidence, just interesting.

[Chet]

26 minutes ago, ..Kev said:

I certainly don't consider that definitive evidence,

Its on the internet so it must be true. 

[thewoodwhisperer]

Rogowski’s thoughts.

[krtwood]

There are two types of linguists,  Prescriptive and Descriptive.  Prescriptivists try to tell people the "right" way to use words.  Descriptivists look at the way people are using words.  Descriptivists acknowledge that once everyone is wrong about about how a word is used they are now right.   No one likes a prescriptivist, even though you're making a book where people are learning the right terms for things.  I think it's just best to acknowledge that in the real world you are going to see the terms spline and key used interchangeably and not worry about trying to define them properly.

 

[Chet]

Looking at you pictures a second time I can see were the second one would be more of what is generally referred to as a splined miter in that it goes all the way through and is done in the glue up process, the same as doing a spline miter in a vertical fashion like the corners of a jewelry box or steamer trunk.  Where as the other is done after the glue drys on the miter.  Maybe the term key comes from the fact that it is a shape other then a rectangular prism like a normal spline.  What would that be then a triangular prism?

[Chestnut]

Somethings do just get lost in time. Example the proper way to pronounce Sakakawea.

Also that definition is a bit vague. After the project is complete and on display how would you differentiate on method? It is possible to cut the  "key" in but install it during the regular glueup, thus making it a spline and even more confusing.

I feel like more people are going to push back on calling it a key. Also is this a case of more correct. Where we can say a key is a type of spline so calling it a spline is correct but more vague than calling it a key?

[Isaac]

44 minutes ago, Chestnut said:

Somethings do just get lost in time. Example the proper way to pronounce Sakakawea.

Also that definition is a bit vague. After the project is complete and on display how would you differentiate on method? It is possible to cut the  "key" in but install it during the regular glueup, thus making it a spline and even more confusing.

I feel like more people are going to push back on calling it a key. Also is this a case of more correct. Where we can say a key is a type of spline so calling it a spline is correct but more vague than calling it a key?

Maybe that is the ultimate answer, that the book provides working definitions that will be used within itself, while also acknowledging the terms are often used interchangeably.

I've been thinking about this since reading this topic yesterday and really can't come up with a reliable distinction. It gets even harder when I think of how the terms are used in other materials. In concrete form work a 2x4 Keyway is sometimes used to connect a concrete footing to a concrete stem wall, so in that case, the "key" is integral to one of the components, so more of what we would probably call a dado joint. 

[Woodenskye]

To me, both examples pictured are splines.  I have a definition of what a key is in my mind but can't articulate it here.  

[Immortan D]

 

22 hours ago, thewoodwhisperer said:

Rogowski’s thoughts.

Also this book (about the keyed miter joint):

In the same book, the word "spline" appears only once and says: "... key or spline..."

I know it's just a consumers' book, nothing scientific.

[Ronn W]

I call one a spline (all the way through) and the other a corner spline (applied after glue up).  Just to be descriptive.

[thewoodwhisperer]

4 hours ago, Chestnut said:

Somethings do just get lost in time. Example the proper way to pronounce Sakakawea.

Also that definition is a bit vague. After the project is complete and on display how would you differentiate on method? It is possible to cut the  "key" in but install it during the regular glueup, thus making it a spline and even more confusing.

I feel like more people are going to push back on calling it a key. Also is this a case of more correct. Where we can say a key is a type of spline so calling it a spline is correct but more vague than calling it a key?

I think you may have touched on the real issue here, with "spline" being the generic term and a "key" being a specific type of spline. So while some may call that simple corner piece that's cut into the frame after glueup a key, it's actually just a specific kind of spline. So then to define a "key" it would be a type of spline that's added after the frame is already glued up. Technically, you can add them during the glueup process but I can't find a single instance where someone does that. Whether it's a corner key or a dovetail key, those are all done after the miter glueup. I feel like we're honing in on it now. 

[Immortan D]

I think folks been using the word "spline" whenever glue is part of the equation. If there is a mechanical lock that works without glue, then the word "key" sounds more adequate.

[Bombarde16]

On 2/25/2018 at 11:51 AM, Llama said:

Flat piece = spline

"dovetail spline" = key 

+1 for Llama's definition.

I would call both of the joints shown in the OP's images "splined miters".  The fact that one gets cut beforehand for insertion during glue-up and the other gets cut after glue-up doesn't change anything.

For me, a keyed miter would be one in which the splines aren't just flat slips of wood.  Something like this:

But I've also seen these referred to as "dovetail splines", so that's confusing, too.

One last thought: pretty much every source you'll find for the jig needed to hold a glued-up frame on its corner as it passes over the table saw describes this as a "spline cutting jig".  If someone can point me to a source that describes it as a "key cutting jig", I'll be happy to take a look.

[Chestnut]

14 minutes ago, Bombarde16 said:

+1 for Llama's definition.

I would call both of the joints shown in the OP's images "splined miters".  The fact that one gets cut beforehand for insertion during glue-up and the other gets cut after glue-up doesn't change anything.

For me, a keyed miter would be one in which the splines aren't just flat slips of wood.  Something like this:

But I've also seen these referred to as "dovetail splines", so that's confusing, too.

One last thought: pretty much every source you'll find for the jig needed to hold a glued-up frame on its corner as it passes over the table saw describes this as a "spline cutting jig".  If someone can point me to a source that describes it as a "key cutting jig", I'll be happy to take a look.

If we accept a key as a type of spline than a dovetail spline is as equally correct as calling the flat pieces keys.

Also the above have been covered but what would this one be called?