Dado vs Groove

[Packard]

I learned woodworking from books and magazines.  Later from the Internet, but in the late 1970s that was not much used.

One book I read early on made a distinction between “dadoes” and “grooves”.  I have always adhered to that distinction.  But I am questioning it lately.

A dado ran across the grain, and a groove ran parallel to the grain.  Plywood, MDF and particle board only had dadoes.

Is anyone still making that distinction?  Sometimes I feel silly doing so.

 

[Muttley000]

I used to consider them distinctly different, but I guess hearing them described what I though was incorrectly so many times changed me over the years.

 

[woodbutcherbower]

It's a 'rebate' in the UK. Doesn't matter which direction it goes in. A 'groove' is something usually cut into the narrow edge of a workpiece, for inserting a weather seal or similar.

 

[Packard]

Who would have thought the Brits would have simplified things?  [big grin]

 

[woodbutcherbower]

Who would have thought the Brits would have simplified things?  [big grin]

[member=74278]Packard[/member] it's because our simple minds can't handle anything more complex, buddy  [big grin]

 

[Crazyraceguy]

It's a 'rebate' in the UK. Doesn't matter which direction it goes in. A 'groove' is something usually cut into the narrow edge of a workpiece, for inserting a weather seal or similar.

I thought a rebate was what we call a rabbet? a cut that is literally on the edge, like an L?
Then what we call dado/groove was called a housing?

I would imagine that both terms were coined long before sheet goods with would confound the grain direction part?

 

[ChuckM]

British woodworker and teacher Paul Sellers refers to a dado as a housing dado and a tongue cut on the edge as a rebate. Rabbets (rebates) and dadoes are not the same thing, otherwise a rabbet dado joint (a tongue housed into a dado) would sound funny. I don't use dadoes (across the grain), rabbets (tongue/notch formed) and grooves -- not groves! --(along the grain) interchangeably.

[attachimg=1]

 

[Packard]

British woodworker and teacher Paul Sellers refers to a dado as a dado housing and a tongue cut on the edge as a rebate. Rabbets (rebates) and dadoes are not the same thing, otherwise a rabbet dado joint (a tongue housed into a dado) would sound funny. I don't use dadoes (across the grain), rabbets (tongue/notch formed) and grooves -- not groves! --(along the grain) interchangeably.

[attachimg=1]

The image shows exactly what I learned 35 years ago.  But in recent years “groove” has grown in disfavor and “dado” seems to be doing the service for both.

 

[Bob D.]

I learned Dado, Groove, and Rabbet also and still refer to them that way.

I'm not changing just because others don't know or care to use the proper terminology.

 

[Bugsysiegals]

I’m a simple man, I just call it a slot! J/K I’ve been calling them dados and now I know there’s a difference depending on grain direction!

 

[Crazyraceguy]

I’m a simple man, I just call it a slot! J/K I’ve been calling them dados and now I know there’s a difference depending on grain direction!

But the original question was "what happens if there is no grain direction?" like MDF, particle board,  plywood (where the grain is going both directions)

 

[tjbnwi]

The face sheet of plywood does have a grain direction. I can order plywood 4x8 or 8x4. 4x8 the dado would run along the long bias, 8x4 the dado would run along the short bias.

For sheets that do not have a face grain, I go with the long bias is a dado, short bias a groove.

Tom

 

[Crazyraceguy]

Yeah, the whole 4 x 8 and 8 x 4 thing confuses the heck out of new guys in the shop. We run into that with laminate sometimes too. Some of the wood grain colors are available either way. Most of them have an X-grain designation too though.

I know it's just a weird personal thing, but I don't like to see a piece of wood that is wider than it is long. The grain should go along the longer direction.

AWI premium standards for laminate faced cabinets say that the grain should run the same direction as the doors. Grain-matched.
Personally, I hate that. IMHO, the grain should go across, just like it would with real wood.
Ok, off-topic rant off....

 

[mino]

The Dado/Groove distinction came to be because of a structural meaning. The grain direction signifficantly affects the strength of the  cut/interface/joint/etc.

I would stick with the functional in naming:
MDF/PB => all cuts are grooves, ak "in the optimal stength direction" as the material is homogenous
Plywood => all are dadoes, aka all are "in the low-strength direction"

This is the same how we tend to say "there is no ripping with Plywood", only cross-cutting. So a cross-cut blade is needed.
In the same way one better consider properly a material swap with plywood where a groove _in_wood_ was originally suppossed to be ... as for a dado, that is absolutely fine.

Some more mumblings:

For a "lateral" force the groove is way stronger. So there are cases where a dado is not an option but a groove is. E.g. close to the edge. That does not even cover the expand/shrink effects are the complete opposite as well.

Now, with sheet goods this has no meaning. E.g. plywood is "weak" like a dado in both cases. Given plywood *behaves like* wood with a dado, I would call it a dado. This is actually funny, as the optimal strength with plywood is to make the pieces from 45-degree cuts. Guess then it would be a groove even in plywood ?!?

Either way, keeping the disctinction is IMO still useful. It forces "The newbie" to think about the physical properties of the material. If anything.

/Goes on to figure out what is what when started writing this .../

 

[tsmi243]

If I cut it with a dado stack, it's a dado. 

Not one lesson  [cool]

 

[semenza]

That is interesting about the plywood grain direction being different and noted as 8' x 4' . But I have often noticed in posts from UK members frequently seeing the length / width sizes given with the length first ...... 8' x 4', 4" x 2", etc.

Seth

 

[ChuckM]

If I cut it with a dado stack, it's a dado. 

Not one lesson  [cool]

That does sound an easy way to tell one from another (though I've done dadoing with a regular saw blade in multiple passes because I'm lazy sometimes).

 

[Michael Kellough]

If I cut it with a dado stack, it's a dado. 

Not one lesson  [cool]

That does sound an easy way to tell one from another (though I've done dadoing with a regular saw blade in multiple passes because I'm lazy sometimes).

When I’m a little less lazy I’ll do the same but with the special flat tooth Forest blade, instead of getting out the dado stack.

 

[Lincoln]

That is interesting about the plywood grain direction being different and noted as 8' x 4' . But I have often noticed in posts from UK members frequently seeing the length / width sizes given with the length first ...... 8' x 4', 4" x 2", etc.

Seth

Same in Australia, length is given first.

 

[Packard]

If I cut it with a dado stack, it's a dado. 

Not one lesson  [cool]

I’ve made tongue and groove panels with a dado blade.  So that is “tongue and dado” panels?

If a road sign says “no left turn” and you turn your steering wheel to the left to make a u-turn, did you make a left turn?