I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the plywood
thickness enough.

--
Mike
Watch for the bounce.
If ya didn't see it, ya didn't feel it.
If ya see it, it didn't go off.
Old Air Force Munitions Saying
IYAAYAS

"asmurff" wrote in message
...
I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the
plywood thickness enough.

--
Mike
Watch for the bounce.
If ya didn't see it, ya didn't feel it.
If ya see it, it didn't go off.
Old Air Force Munitions Saying
IYAAYAS


It really depends on humidity and things like that. I'm think'n you're gonna
have some expansion problems.

If you're afraid to jump out of a
perfectly good H-19 into a jungle
full of gooks running around shooting
up the place, you need to be in the Navy.
Old Air Commando Saying

asmurff wrote:
I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the
plywood thickness enough.

How smooth/flat is the plywood?

Take a piece of scrap, cut a dado the width you think will work. Too
sloppy? Too tight? Cut another dado wider or narrower as the case may be.

IOW, use your head fer cryin' out loud!

--

dadiOH
____________________________

dadiOH's dandies v3.06...
....a help file of info about MP3s, recording from
LP/cassette and tips & tricks on this and that.
Get it at http://mysite.verizon.net/xico

"asmurff" wrote in message
...
I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the
plywood thickness enough.


Do you want to be able to slide the piece out or will it be permanent? Want
to slide it out, I'd go at least 1/8" wider. Want it to be permanent, a
perfect fit will be much stronger.

On Fri, 23 May 2008 16:35:46 -0600, "asmurff"
wrote:

I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the plywood
thickness enough.


Plywood varies in thickness, not just from sheet to sheet, but in
different places on a single sheet.

Better quality cabinet grade plywood varies less but still varies.

What I have come to do is to not use dadoes that are the full
thickness of the ply. I usually make a dado that is in width from a
third to a half of the nominal thickness of the ply. Then I cut a
tongue in the other piece to match that width.

This takes the variation in thickness out of play.

Let's say that you are making a bookcase out of 3/4" plywood. You
make a dado that is about 5/16" wide on the vertical (side) pieces.
Then you make a tongue on the bottom of your horizontal (shelf) pieces
by setting your tablesaw fence 5/16" away from the nearest edge of the
blade. You will wind up with an offset tongue that will fit
perfectly.

The offset tongue should be made on the bottom face of the shelf so
that the laminations of the shelf ply are loaded in compression,
rather than being under tension.

I usually make thelength of the tongue very slightly shorter than the
depth of the dado, so that the glue has somewhere to go when you clamp
up. By 'very slighty' I mean no more than the thickness of a sheet of
paper.


HTH



Tom Watson
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1

Okay I know plywood comes in varied thickness this sheet happens to be 45/64
of an inch. I was planning on cutting the dado at 47/64 to give me a tad of
room on each side. The piece will be permanent with cleats below, but yes
I'd still like it to look good even if it will only be seen in my
garage/shop.

DadiOH I do use my head which is why I asked here, I thought there might be
a pat answer to the question, if there isn't I'm more than willing to listen
to the group but don't insult me.

--
Mike
Watch for the bounce.
If ya didn't see it, ya didn't feel it.
If ya see it, it didn't go off.
Old Air Force Munitions Saying
IYAAYAS
"Tom Watson" wrote in message
...
On Fri, 23 May 2008 16:35:46 -0600, "asmurff"
wrote:

I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the
plywood
thickness enough.


Plywood varies in thickness, not just from sheet to sheet, but in
different places on a single sheet.

Better quality cabinet grade plywood varies less but still varies.

What I have come to do is to not use dadoes that are the full
thickness of the ply. I usually make a dado that is in width from a
third to a half of the nominal thickness of the ply. Then I cut a
tongue in the other piece to match that width.

This takes the variation in thickness out of play.

Let's say that you are making a bookcase out of 3/4" plywood. You
make a dado that is about 5/16" wide on the vertical (side) pieces.
Then you make a tongue on the bottom of your horizontal (shelf) pieces
by setting your tablesaw fence 5/16" away from the nearest edge of the
blade. You will wind up with an offset tongue that will fit
perfectly.

The offset tongue should be made on the bottom face of the shelf so
that the laminations of the shelf ply are loaded in compression,
rather than being under tension.

I usually make thelength of the tongue very slightly shorter than the
depth of the dado, so that the glue has somewhere to go when you clamp
up. By 'very slighty' I mean no more than the thickness of a sheet of
paper.


HTH



Tom Watson
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1

Thanx Leon you answered a question for this project and a future one.

--
Mike
Watch for the bounce.
If ya didn't see it, ya didn't feel it.
If ya see it, it didn't go off.
Old Air Force Munitions Saying
IYAAYAS
"Leon" wrote in message
...

"asmurff" wrote in message
...
I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the
plywood thickness enough.


Do you want to be able to slide the piece out or will it be permanent?
Want to slide it out, I'd go at least 1/8" wider. Want it to be
permanent, a perfect fit will be much stronger.

asmurff wrote:

DadiOH I do use my head which is why I asked here, I thought there
might be a pat answer to the question, if there isn't I'm more than
willing to listen to the group but don't insult me.

1. I gave you a perfectly acceptable answer

2. I wasn't trying to insult you - ergo the smiley - but was pointing out
that you could have easily and (most) effectively answered your question for
yourself.
___________

Pat Answers
Ah, yes...the pat answer...the be all and end all of existence.
Unfortunately, there is rarely a pat answer to anything other than "it
depends".

In your case, it depended on the type and quality of the plywood, how tight
you wanted the dado/tongue to be, how long they were to be and what you
meant by "Is 1/32" wider than the plywood thickness enough." Enough for
what? To put together? To stand without support? To glue well?

In my case, I want what I think of as a "snick" fit; the tongue goes into
the dado easily with moderate pressure, doesn't wobble and when separating
the pieces there is sort of a "snick" feel/sound...sort of like popping your
cheek with a finger And no, I can't better describe it. Trouble is, a fit
that is fine on, say, a 4" dado/tongue probably won't be if the dado/tongue
is 30"...it will probably feel too tight. It would probably be OK if I
slightly beveled the edges of the tongue - which I regularly do either with
a small plane or a four-in-hand file depending on the material - but even
then it will likely take considerable pressure to get the tongue into the
groove/dado.

Tom Watson gave you a nice way to make a tongue that is reasonably precise
in size. Works most of the time; however, it would be very difficult to
impossible to cut a tongue in that manner on the four foot end of a sheet of
4x8 foot plywood. Or on the short end a 1x6 foot one either
______________

I think most people that have read newsgroups - ANY newsgroup - for a while
would agree that many of the questions could easily and more effectively be
answered by the poster if s/he only thought about it for a moment and/or
drew on their empirical experience.

That doesn't mean I don't think people *shouldn't* ask questions - many
times the asking provides answers that are useful though not necessarily
germane - merely that they could often work out a solution for themselves
and in so doing they have a solution (and brain exercise) that can be
modified for use in other circumstances.

--

dadiOH
____________________________

dadiOH's dandies v3.06...
....a help file of info about MP3s, recording from
LP/cassette and tips & tricks on this and that.
Get it at http://mysite.verizon.net/xico

Sorry I grouched I was having a lousy day with my arthritis, which can turn
me into a crab. I asked the question after I had quit working for the day
and was doing the math on a couple of cuts I need to make today and thought
I ask here to see if there was a normal procedure used by most. I was
planning on cutting a test piece with the info I got here in mind. The
plywood is the best grade Home Depot sells with one face pre-sanded and the
other face is fairly smooth also. It isn't for a piece of fine furniture,
but a Flip-Top Tool Stand, I got the plans from "The Complete Small Shop". I
know how to make the piece fit into the dado I just wasn't sure if I needed
expansion room and if so how much. If you had left off the "IOW, use your
head fer cryin' out loud! " I would have said okay I'll try that.


Mike
Watch for the bounce.
If ya didn't see it, ya didn't feel it.
If ya see it, it didn't go off.
Old Air Force Munitions Saying
IYAAYAS
"dadiOH" wrote in message
news1IZj.3409$ED6.443@trnddc02...
asmurff wrote:
I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the
plywood thickness enough.

How smooth/flat is the plywood?

Take a piece of scrap, cut a dado the width you think will work. Too
sloppy? Too tight? Cut another dado wider or narrower as the case may
be.

IOW, use your head fer cryin' out loud!

--

dadiOH
____________________________

dadiOH's dandies v3.06...
...a help file of info about MP3s, recording from
LP/cassette and tips & tricks on this and that.
Get it at http://mysite.verizon.net/xico

On May 23, 7:36 pm, Tom Watson wrote:
...
I usually make a dado that is in width from a
third to a half of the nominal thickness of the ply. Then I cut a
tongue in the other piece to match that width.
...
The offset tongue should be made on the bottom face of the shelf so
that the laminations of the shelf ply are loaded in compression,
rather than being under tension.

I usually make thelength of the tongue very slightly shorter than the
depth of the dado, so that the glue has somewhere to go when you clamp
up. By 'very slighty' I mean no more than the thickness of a sheet of
paper.

That makes good sense, but I would be inclined to make
the tongue more like 2/3 to 3/4 of the thickness. I don't see
any advantage to making it less.

If it is less than half, the some of the veneers that
aren't glued into the dado will be in tension.

--

FF

On Sat, 24 May 2008 11:10:52 -0700 (PDT), Fred the Red Shirt
wrote:

On May 23, 7:36 pm, Tom Watson wrote:
...
I usually make a dado that is in width from a
third to a half of the nominal thickness of the ply. Then I cut a
tongue in the other piece to match that width.
...
The offset tongue should be made on the bottom face of the shelf so
that the laminations of the shelf ply are loaded in compression,
rather than being under tension.

I usually make thelength of the tongue very slightly shorter than the
depth of the dado, so that the glue has somewhere to go when you clamp
up. By 'very slighty' I mean no more than the thickness of a sheet of
paper.



That makes good sense, but I would be inclined to make
the tongue more like 2/3 to 3/4 of the thickness. I don't see
any advantage to making it less.


Then you would only have 3/16" - 1/4" of meat left beyond the groove
when using this joint at the top or the bottom of a carcase. Your
theory works fine for a shelf or divider in the middle of the panel
but would require different joinery for the corners, which is not
optimal.



If it is less than half, the some of the veneers that
aren't glued into the dado will be in tension.

The tongue is formed on the bottom part of the thickness of the board.
The shearing load is compressive throughout the thickness of the
board.

Only at the bottom of a carcase, where the tongue would, of necessity,
be formed on the top part of the thickness of the board, would there
be tension on the glue lines of the ply. The reason that you can get
away with that is because you can have a frame below the carcase at
this point.






Regards,

Tom

Thos.J.Watson - Cabinetmaker
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1

asmurff wrote:

I know how to
make the piece fit into the dado I just wasn't sure if I needed
expansion room and if so how much.

You don't need any expansion room.

--

dadiOH
____________________________

dadiOH's dandies v3.06...
....a help file of info about MP3s, recording from
LP/cassette and tips & tricks on this and that.
Get it at http://mysite.verizon.net/xico

It depends upon the respective sheets of plywood and the length of the
dado/cut. With rough (CDX) stuff more tolerance is required.
Similarly, as the length of the dado/cut is increased - e,g, slot is
longer - more tolerance may be required. Conversly with a xmall slot,
A/C or better sanded ten-ply furniture-grade plywood, less tolerance
(perhaps your 1/32") will do nicely.

The suggested 1/8" inch is best combined with a technique of cutting
down the inserted piece where it fits into the dado groove and cutting
the dado less than the thickness of the piece to be inserted. In this
way, you achieve the looser tolerances and still hide the joint seam.

On May 23, 7:36 pm, Tom Watson wrote:
On Fri, 23 May 2008 16:35:46 -0600, "asmurff"
wrote:

I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the plywood
thickness enough.

Plywood varies in thickness, not just from sheet to sheet, but in
different places on a single sheet.

Better quality cabinet grade plywood varies less but still varies.

What I have come to do is to not use dadoes that are the full
thickness of the ply. I usually make a dado that is in width from a
third to a half of the nominal thickness of the ply. Then I cut a
tongue in the other piece to match that width.

This takes the variation in thickness out of play.

I don't think that takes the variation out of play, it just hides it
somewhat. Generally you'll see plywood that is a bit wavy in
thickness, but rarely does it taper. Cutting a tongue like you
suggest will remove the waviness from one side of the board and the
wavy side, being the tongue on the bottom, is generally more hidden.
That technique doesn't address the waviness of the plywood sides. The
perfectly straight rabbet cut on the shelf will be on the top and
you'll still see the waviness that's in the uprights.

R

On Sun, 25 May 2008 08:14:53 -0700 (PDT), RicodJour
wrote:

On May 23, 7:36 pm, Tom Watson wrote:
On Fri, 23 May 2008 16:35:46 -0600, "asmurff"
wrote:

I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the plywood
thickness enough.

Plywood varies in thickness, not just from sheet to sheet, but in
different places on a single sheet.

Better quality cabinet grade plywood varies less but still varies.

What I have come to do is to not use dadoes that are the full
thickness of the ply. I usually make a dado that is in width from a
third to a half of the nominal thickness of the ply. Then I cut a
tongue in the other piece to match that width.

This takes the variation in thickness out of play.

I don't think that takes the variation out of play, it just hides it
somewhat. Generally you'll see plywood that is a bit wavy in
thickness, but rarely does it taper. Cutting a tongue like you
suggest will remove the waviness from one side of the board and the
wavy side, being the tongue on the bottom, is generally more hidden.
That technique doesn't address the waviness of the plywood sides. The
perfectly straight rabbet cut on the shelf will be on the top and
you'll still see the waviness that's in the uprights.

R


The point about variation in thickness was that, if you cut a ¾" width
dado to receive shelves, and some of the shelf material is greater or
less than ¾" thick, you will be too tight on some shelves and too
loose on others.

Machining a tongue using the method described allows you to create a
tongue that is of consistent thickness throughout its length. You
will then have a tongue of consistent thickness and length mating to a
groove of consistent width and depth. This is required for a good
joint that has a consistent glue line.

The waviness that you describe, which I take to be a combination of
variation in thickness and the cup, or even snakiness (alternating
concavity and convexity relative to a straight line) of the material
can be moderated by good clamping and gluing technique.

I've made a test joint using construction grade plywood, which was
cupped and varied in thickness throughout by as much as .031". I
tried to find some CDX in the shop but the closest I could come was
some leftover decking ply, still pretty much a worst case scenario
when we are really talking about making cabinets, typically out of
much better material.

I've photographed both the top and bottom of the 'shelf' where it
joins the 'side'. You can judge whether or not it is a good joint and
whether or not there is any 'waviness'.

The photos are on ABPW.




Regards,

Tom

Thos.J.Watson - Cabinetmaker
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1

On Sat, 24 May 2008 14:09:26 GMT, "dadiOH" wrote:


Tom Watson gave you a nice way to make a tongue that is reasonably precise
in size. Works most of the time; however, it would be very difficult to
impossible to cut a tongue in that manner on the four foot end of a sheet of
4x8 foot plywood. Or on the short end a 1x6 foot one either


I would use the same technique on ply up to about four or five feet in
length but would use a different one on the longer stuff.

The short edge of the 1x6 is no problem. If you don't like the idea
of running it through by hand, a typical sliding fixture with clamps
will hold the piece safely.

I've posted some pictures of this joint on ABPW.



Regards,

Tom

Thos.J.Watson - Cabinetmaker
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1

On Fri, 23 May 2008 16:35:46 -0600, "asmurff"
wrote:

I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the plywood
thickness enough.


I've posted pictures of the T+G joint that I described in another
reply.

The photos are on ABPW.



Regards,

Tom

Thos.J.Watson - Cabinetmaker
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1

On Sun, 25 May 2008 20:54:50 -0400, Tom Watson
wrote:

On Fri, 23 May 2008 16:35:46 -0600, "asmurff"
wrote:

I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the plywood
thickness enough.


I've posted pictures of the T+G joint that I described in another
reply.

The photos are on ABPW.



Regards,

Tom

Thos.J.Watson - Cabinetmaker
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1



Someone reminded me that not everyone can get ABPW, so I've put them
up on the website.



http://home.comcast.net/~tjwatson1/o...Close%20Up.jpg

http://home.comcast.net/~tjwatson1/o...From%20Top.jpg

http://home.comcast.net/~tjwatson1/o...om%20Above.jpg

http://home.comcast.net/~tjwatson1/o...om%20Below.jpg

http://home.comcast.net/~tjwatson1/o...0Of%20Side.jpg





Regards,

Tom

Thos.J.Watson - Cabinetmaker
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1

"Tom Watson" wrote

Someone reminded me that not everyone can get ABPW, so I've put them
up on the website.

Good job Tom. I appreciate the pictures.

I have certainly had to build things with less than optimum materials. I
have even used this technique before. I called it a rabbetted dado joint.
(Is that even a joint name?)

On May 24, 6:41 pm, Tom Watson wrote:
On Sat, 24 May 2008 11:10:52 -0700 (PDT), Fred the Red Shirt

...
That makes good sense, but I would be inclined to make
the tongue more like 2/3 to 3/4 of the thickness. I don't see
any advantage to making it less.

Then you would only have 3/16" - 1/4" of meat left beyond the groove
when using this joint at the top or the bottom of a carcase. Your
theory works fine for a shelf or divider in the middle of the panel
but would require different joinery for the corners, which is not
optimal.


Ah! that makes sense. I was only thinking of shelves.



If it is less than half, the some of the veneers that
aren't glued into the dado will be in tension.

The tongue is formed on the bottom part of the thickness of the board.
The shearing load is compressive throughout the thickness of the
board.

Only at the bottom of a carcase, where the tongue would, of necessity,
be formed on the top part of the thickness of the board, would there
be tension on the glue lines of the ply. The reason that you can get
away with that is because you can have a frame below the carcase at
this point.


I don't follow what you mean by 'shearing load is compressive'.
Shear, compression, and tension are three distinct orientations
of stress.

For a beam with a symmetrical cross-section, the sheer
due to bending is maximum midway between the upper
and lower surfaces. It is zero at the upper and lower surfaces.
From that midpoint up the stress is compressive, and maximum
at the upper surface. From the midpoint down the stress
is tensile and maximum at the lower surface.

--

FF

On Sun, 25 May 2008 19:11:03 -0700 (PDT), Fred the Red Shirt
wrote:

don't follow what you mean by 'shearing load is compressive'.
Shear, compression, and tension are three distinct orientations
of stress.

For a beam with a symmetrical cross-section, the sheer
due to bending is maximum midway between the upper
and lower surfaces. It is zero at the upper and lower surfaces.
From that midpoint up the stress is compressive, and maximum
at the upper surface. From the midpoint down the stress
is tensile and maximum at the lower surface.


If you look at the joint in the photos, is it more likely to
delaminate under load on the shelf with the tongue at the bottom, or
with the tongue at the top?



Regards,

Tom

Thos.J.Watson - Cabinetmaker
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1

On May 26, 2:42 am, Tom Watson wrote:
On Sun, 25 May 2008 19:11:03 -0700 (PDT), Fred the Red Shirt

wrote:
don't follow what you mean by 'shearing load is compressive'.
Shear, compression, and tension are three distinct orientations
of stress.

For a beam with a symmetrical cross-section, the sheer
due to bending is maximum midway between the upper
and lower surfaces. It is zero at the upper and lower surfaces.
From that midpoint up the stress is compressive, and maximum
at the upper surface. From the midpoint down the stress
is tensile and maximum at the lower surface.

If you look at the joint in the photos, is it more likely to
delaminate under load on the shelf with the tongue at the bottom, or
with the tongue at the top?


At the top, of course.

My point is that making the tenon less than half the
thickness of the shelf also makes it more likely to
delaminate than if the tenon is at least half the
thickness.

Nice work, BTW.

--

FF

On 5/23/08 7:36 PMMay 23, "Tom Watson" wrote:

On Fri, 23 May 2008 16:35:46 -0600, "asmurff"
wrote:

I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the plywood
thickness enough.

What I have come to do is to not use dadoes that are the full
thickness of the ply. I usually make a dado that is in width from a
third to a half of the nominal thickness of the ply. Then I cut a
tongue in the other piece to match that width.

Tom,

The photos that you posted in a.b.p.w illustrate this very well. You have
added a technique to my bag of tricks. I can see how this can be used to
advantage.

I would have thought that the tongue would be thicker - 1/2 to 2/3 the width
of the shelving.

The offset tongue should be made on the bottom face of the shelf so
that the laminations of the shelf ply are loaded in compression,
rather than being under tension.

That makes sense. Thanks for the rationale behind that part of the
technique.

Thanks for the links to the images!

When I do it, i cut the top and bottom of the "shelf" edges about an
eight or so to make the tongue. But your approach seems to leave as
nice a line as mine with less work!

Thanks, again for the links to the images.

Robert Haar wrote:
You have
added a technique to my bag of tricks. I can see how this can be used to
advantage.


Make that two bags.

Since wood should be in compression (vs. tension) as often as possible,
I think this is an excellent technique and wish I'd heard of it before.