Guidance please for building a curved lamination

"Dick Snyder" <[email protected]> wrote in message
news:[email protected]...
> I'm not sure how to compute the bending radius. Maybe you can help me.
> Here is what I know. The curved top piece of the bookcase will span a
> width of 45". The highest point of the curve above a flat surface for a
> reference point will be 8".

Don't compute it... just do it!

Place two nails 45 inches apart and place a mark 8" above the mid point.
Then take a thin flexible board, put it up against the nails and bend it up
to to the mid-point mark. Then trace the arc of the board with a pencil. You
can tinker with this basic approach a bit to get your ending and mid-points
just where you want them.

John

> OK. So how did you compute it :-)

I've had to do this a few times recently - I puzzled over it for quite
a while at first, and finally realized it's all a matter of applying
the pythagorean theorem. a^2 + b^2 = c^2 (or maybe there's an easier
way I haven't found yet, in which case I hope someone will enlighten
me...)

You know one side of your triangle with the given width. Let's call
that a, and it is 22.5" (half of your total width).
You're looking for the hypotenuse, which is the radius, which we'll
call c.
The third edge of the triangle is the radius minus 8" (your rise), so
we'll call that b, or (c-8).
Pythagoreus says a^2 + b^2 = c^2, so now as my 8th grade algebra
teacher used to say, plug-n-chug.

22.5^2 + (c-8)^2 = c^2
506.25 + c^2 - 16c +64 = c^2
570.25 = 16c
c = 35.604625, or just a hair (1/128) under 35 39/64, or practically,
I'd use 35 5/8.
(It's a lot easier if you can draw a picture...)
Andy

Sat, Jul 22, 2006, 7:10am [email protected] (Dick=A0Snyder)
doth claimeth:
<snip> Here is my question. I know you have to build the lamination on a
form <snip>

Not if you K.I.S.S. it.

You're gonna paint. So laminate plywood to the proper thickness,
or use solid wood, cut to shape, no bending. No prob.

For those of you that don't know, K.I.S.S. - Keep It Simple Stupid.



JOAT
Politician \Pol`i*ti"cian\, n. Latin for career criminal

It took me awhile to figure out where the triangle was but as you said, draw
a picture. Clever solution. Thanks.


"Andy" <[email protected]> wrote in message
news:[email protected]...
>> OK. So how did you compute it :-)
>
> I've had to do this a few times recently - I puzzled over it for quite
> a while at first, and finally realized it's all a matter of applying
> the pythagorean theorem. a^2 + b^2 = c^2 (or maybe there's an easier
> way I haven't found yet, in which case I hope someone will enlighten
> me...)
>
> You know one side of your triangle with the given width. Let's call
> that a, and it is 22.5" (half of your total width).
> You're looking for the hypotenuse, which is the radius, which we'll
> call c.
> The third edge of the triangle is the radius minus 8" (your rise), so
> we'll call that b, or (c-8).
> Pythagoreus says a^2 + b^2 = c^2, so now as my 8th grade algebra
> teacher used to say, plug-n-chug.
>
> 22.5^2 + (c-8)^2 = c^2
> 506.25 + c^2 - 16c +64 = c^2
> 570.25 = 16c
> c = 35.604625, or just a hair (1/128) under 35 39/64, or practically,
> I'd use 35 5/8.
> (It's a lot easier if you can draw a picture...)
> Andy
>

I'm not sure how to compute the bending radius. Maybe you can help me. Here
is what I know. The curved top piece of the bookcase will span a width of
45". The highest point of the curve above a flat surface for a reference
point will be 8".

"Lew Hodgett" <[email protected]> wrote in message
news:[email protected]...
> Dick Snyder wrote:
> > My daughter has asked me to build a bookcase for her baby's
> nursery. She saw
> > something on-line that she likes. It has a curved top. I think I
> will build
> > the bookcase out of birch as it will be painted and I am thinking of
> > laminating 3 1/4" pieces of birch plywood to do the curved top.
>
> <snip>
>
> Make sure you use what is known as "bending plywood".
>
> Around here, 1/4" "bending" poplar is readily available.
>
> The amount of "springback" is a function of the lamination thickness and
> the bending radius, so can't answer your question.
>
> I'd use epoxy with a slow hardner.
>
> It will give you good "open time" and provide a rock solid lamination.
>
> Don't be in a hurry to take it out of the clamps.
>
> Have fun.
>
> Lew

OK. So how did you compute it :-)
"CW" <[email protected]> wrote in message
news:[email protected]...
> 35 5/8 radius. Actually 35.641 but close enough.
>
> "Dick Snyder" <[email protected]> wrote in message
> news:[email protected]...
>> I'm not sure how to compute the bending radius. Maybe you can help me.
> Here
>> is what I know. The curved top piece of the bookcase will span a width of
>> 45". The highest point of the curve above a flat surface for a reference
>> point will be 8".
>>
>> "Lew Hodgett" <[email protected]> wrote in message
>> news:[email protected]...
>> > Dick Snyder wrote:
>> > > My daughter has asked me to build a bookcase for her baby's
>> > nursery. She saw
>> > > something on-line that she likes. It has a curved top. I think I
>> > will build
>> > > the bookcase out of birch as it will be painted and I am thinking of
>> > > laminating 3 1/4" pieces of birch plywood to do the curved top.
>> >
>> > <snip>
>> >
>> > Make sure you use what is known as "bending plywood".
>> >
>> > Around here, 1/4" "bending" poplar is readily available.
>> >
>> > The amount of "springback" is a function of the lamination thickness
>> > and
>> > the bending radius, so can't answer your question.
>> >
>> > I'd use epoxy with a slow hardner.
>> >
>> > It will give you good "open time" and provide a rock solid lamination.
>> >
>> > Don't be in a hurry to take it out of the clamps.
>> >
>> > Have fun.
>> >
>> > Lew
>>
>>
>
>

On Sat, 22 Jul 2006 07:10:04 -0400, "Dick Snyder"
<[email protected]> wrote:

>My daughter has asked me to build a bookcase for her baby's nursery. She saw
>something on-line that she likes. It has a curved top. I think I will build
>the bookcase out of birch as it will be painted and I am thinking of
>laminating 3 1/4" pieces of birch plywood to do the curved top.
>
>Here is my question. I know you have to build the lamination on a form with
>a tighter radius than you want to end up with as the wood with spring back a
>bit when you remove the clamps after gluing up the lamination. Is there some
>guidance people can give me on how to figure out that tighter radius??

I recently did a test with 3 layers of 1/8" baltic birch ply and it
didn't spring back at all. I arranged the grain of the outer plys so
they were parallel to the bend. And the 3/8" built up is hard as a
rock.


-Leuf

"Dick Snyder" <[email protected]> wrote in message
news:[email protected]...
> My daughter has asked me to build a bookcase for her baby's nursery. She
> saw something on-line that she likes. It has a curved top. I think I will
> build the bookcase out of birch as it will be painted and I am thinking of
> laminating 3 1/4" pieces of birch plywood to do the curved top.
>
> Here is my question. I know you have to build the lamination on a form
> with a tighter radius than you want to end up with as the wood with spring
> back a bit when you remove the clamps after gluing up the lamination. Is
> there some guidance people can give me on how to figure out that tighter
> radius??

The other option is to take your best guess on the radius, create the bent
laminated parts and then, if your resulting dimensions are off a bit, adjust
the dimensions of the rest of the bookcase to work with the laminated
pieces.

John

Dick Snyder wrote:
> Hmm. I had planned to wet one surface of each of the three pieces
of plywood
> and then put gorilla glue on the facing dry surface before clamping.

> I take
> it you would still go with epoxy and a slow hardener??

Absolutely.

The Gougeon Brothers (West System) has a lot of small packages
available and good tech service.

Available lots of places, especially those serving the marine industry.

Never checked, but try a Google.

Lew

Thanks for the tip.


"Phisherman" <[email protected]> wrote in message
news:[email protected]...
> On Sat, 22 Jul 2006 07:10:04 -0400, "Dick Snyder"
> <[email protected]> wrote:
>
>>My daughter has asked me to build a bookcase for her baby's nursery. She
>>saw
>>something on-line that she likes. It has a curved top. I think I will
>>build
>>the bookcase out of birch as it will be painted and I am thinking of
>>laminating 3 1/4" pieces of birch plywood to do the curved top.
>>
>>Here is my question. I know you have to build the lamination on a form
>>with
>>a tighter radius than you want to end up with as the wood with spring back
>>a
>>bit when you remove the clamps after gluing up the lamination. Is there
>>some
>>guidance people can give me on how to figure out that tighter radius??
>>
>>TIA.
>>
>>Dick Snyder
>>
>
> There are many factors depending on how you go about it, the radius,
> the number of laminations, and the wood. As a guideline I'd use 4% of
> the radius.

Did you wet the baltic birch? What glue did you use?
"Leuf" <[email protected]> wrote in message
news:[email protected]...
> On Sat, 22 Jul 2006 07:10:04 -0400, "Dick Snyder"
> <[email protected]> wrote:
>
>>My daughter has asked me to build a bookcase for her baby's nursery. She
>>saw
>>something on-line that she likes. It has a curved top. I think I will
>>build
>>the bookcase out of birch as it will be painted and I am thinking of
>>laminating 3 1/4" pieces of birch plywood to do the curved top.
>>
>>Here is my question. I know you have to build the lamination on a form
>>with
>>a tighter radius than you want to end up with as the wood with spring back
>>a
>>bit when you remove the clamps after gluing up the lamination. Is there
>>some
>>guidance people can give me on how to figure out that tighter radius??
>
> I recently did a test with 3 layers of 1/8" baltic birch ply and it
> didn't spring back at all. I arranged the grain of the outer plys so
> they were parallel to the bend. And the 3/8" built up is hard as a
> rock.
>
>
> -Leuf

Hmm. I had planned to wet one surface of each of the three pieces of plywood
and then put gorilla glue on the facing dry surface before clamping. I take
it you would still go with epoxy and a slow hardener?? If so, any
particular brand of epoxy? I have not used it much for anything but repairs
and assembling golf clubs so my knowledge is pretty limited.


"Lew Hodgett" <[email protected]> wrote in message
news:[email protected]...
> Dick Snyder wrote:
> > My daughter has asked me to build a bookcase for her baby's
> nursery. She saw
> > something on-line that she likes. It has a curved top. I think I
> will build
> > the bookcase out of birch as it will be painted and I am thinking of
> > laminating 3 1/4" pieces of birch plywood to do the curved top.
>
> <snip>
>
> Make sure you use what is known as "bending plywood".
>
> Around here, 1/4" "bending" poplar is readily available.
>
> The amount of "springback" is a function of the lamination thickness and
> the bending radius, so can't answer your question.
>
> I'd use epoxy with a slow hardner.
>
> It will give you good "open time" and provide a rock solid lamination.
>
> Don't be in a hurry to take it out of the clamps.
>
> Have fun.
>
> Lew

Dick Snyder wrote:
> Here is a link to what my daughter wants me to build.
>
>
http://www.target.com/gp/detail.html/ref=br_1_8/602-0450012-2843051?%5Fencoding=UTF8&frombrowse=1&asin=B000CCEV92
>
> As you can see the top is a complex curve but I may just build a
simple
> curve. The top is 12" deep and has to span the book case which is
45" wide.

Looked at the piece.

Interesting, but not too difficult.

My guess is you will spend more time building the fixture than you
will laminating the piece.

As a suggestion, look at Fred Bingham's book, Practical Yacht Joinery.

As you can imagine, there are lots of laminations when you build a boat.

Lew

I guess I don't follow you. Here is a link to what my daughter wants me to
build.

http://www.target.com/gp/detail.html/ref=br_1_8/602-0450012-2843051?%5Fencoding=UTF8&frombrowse=1&asin=B000CCEV92

How would I cut solid wood to shape?


"J T" <[email protected]> wrote in message
news:[email protected]...
Sat, Jul 22, 2006, 7:10am [email protected] (Dick Snyder)
doth claimeth:
<snip> Here is my question. I know you have to build the lamination on a
form <snip>

Not if you K.I.S.S. it.

You're gonna paint. So laminate plywood to the proper thickness,
or use solid wood, cut to shape, no bending. No prob.

For those of you that don't know, K.I.S.S. - Keep It Simple Stupid.



JOAT
Politician \Pol`i*ti"cian\, n. Latin for career criminal

On Sat, 22 Jul 2006 07:10:04 -0400, "Dick Snyder"
<[email protected]> wrote:

>My daughter has asked me to build a bookcase for her baby's nursery. She saw
>something on-line that she likes. It has a curved top. I think I will build
>the bookcase out of birch as it will be painted and I am thinking of
>laminating 3 1/4" pieces of birch plywood to do the curved top.
>
>Here is my question. I know you have to build the lamination on a form with
>a tighter radius than you want to end up with as the wood with spring back a
>bit when you remove the clamps after gluing up the lamination. Is there some
>guidance people can give me on how to figure out that tighter radius??
>
>TIA.
>
>Dick Snyder
>

There are many factors depending on how you go about it, the radius,
the number of laminations, and the wood. As a guideline I'd use 4% of
the radius.

Dick Snyder wrote:
> My daughter has asked me to build a bookcase for her baby's
nursery. She saw
> something on-line that she likes. It has a curved top. I think I
will build
> the bookcase out of birch as it will be painted and I am thinking of
> laminating 3 1/4" pieces of birch plywood to do the curved top.

<snip>

Make sure you use what is known as "bending plywood".

Around here, 1/4" "bending" poplar is readily available.

The amount of "springback" is a function of the lamination thickness
and the bending radius, so can't answer your question.

I'd use epoxy with a slow hardner.

It will give you good "open time" and provide a rock solid lamination.

Don't be in a hurry to take it out of the clamps.

Have fun.

Lew

35 5/8 radius. Actually 35.641 but close enough.

"Dick Snyder" <[email protected]> wrote in message
news:[email protected]...
> I'm not sure how to compute the bending radius. Maybe you can help me.
Here
> is what I know. The curved top piece of the bookcase will span a width of
> 45". The highest point of the curve above a flat surface for a reference
> point will be 8".
>
> "Lew Hodgett" <[email protected]> wrote in message
> news:[email protected]...
> > Dick Snyder wrote:
> > > My daughter has asked me to build a bookcase for her baby's
> > nursery. She saw
> > > something on-line that she likes. It has a curved top. I think I
> > will build
> > > the bookcase out of birch as it will be painted and I am thinking of
> > > laminating 3 1/4" pieces of birch plywood to do the curved top.
> >
> > <snip>
> >
> > Make sure you use what is known as "bending plywood".
> >
> > Around here, 1/4" "bending" poplar is readily available.
> >
> > The amount of "springback" is a function of the lamination thickness and
> > the bending radius, so can't answer your question.
> >
> > I'd use epoxy with a slow hardner.
> >
> > It will give you good "open time" and provide a rock solid lamination.
> >
> > Don't be in a hurry to take it out of the clamps.
> >
> > Have fun.
> >
> > Lew
>
>

On Sun, 23 Jul 2006 06:15:06 -0400, "Dick Snyder"
<[email protected]> wrote:

>Did you wet the baltic birch? What glue did you use?

Nope, it wasn't that much of a bend, and the 1/8" 3 ply is pretty
flexible if you go with the face grain parallel to the bend. I used
regular yellow glue.


-Leuf

The top is three pieces all cut with a router and templates.

You need to buy the article to get a full understanding of
what the guy did.

It appears to be very similar to the piece at Target.

Dick Snyder wrote:

> Here is a link to what my daughter wants me to build.
>
> http://www.target.com/gp/detail.html/ref=br_1_8/602-0450012-2843051?%5Fencoding=UTF8&frombrowse=1&asin=B000CCEV92
>
> As you can see the top is a complex curve but I may just build a simple
> curve. The top is 12" deep and has to span the book case which is 45" wide.
> I couldn't guess from the woodsmith link you sent in your posting what they
> did to build the curved top unless it is only a false front edge and the
> inside (behind the curved front edge) is really flat.

"Dick Snyder" wrote...

> I am thinking of
> laminating 3 1/4" pieces of birch plywood to do the curved top.
>
> Here is my question. I know you have to build the lamination on a form
with
> a tighter radius than you want to end up with as the wood with spring back
a
> bit when you remove the clamps after gluing up the lamination. Is there
some
> guidance people can give me on how to figure out that tighter radius??


Springback is usually a consideration when making bent laminations from
solid stock. If you do make the top from 1/4" ply laminations, it will
certainly spring back some, so I'd do as John G suggests and take your best
shot, then build the casework to match the end result of the lamination.

OTOH, there are some swell products out there made for the use, such as
bending birch, wacky wood, and pre-kerfed MDF that will really stay put when
constructed as a balanced lamination on a form.

--
Timothy Juvenal
www.tjwoodworking.com

Here is a link to what my daughter wants me to build.

http://www.target.com/gp/detail.html/ref=br_1_8/602-0450012-2843051?%5Fencoding=UTF8&frombrowse=1&asin=B000CCEV92

As you can see the top is a complex curve but I may just build a simple
curve. The top is 12" deep and has to span the book case which is 45" wide.
I couldn't guess from the woodsmith link you sent in your posting what they
did to build the curved top unless it is only a false front edge and the
inside (behind the curved front edge) is really flat.

Dick


"Pat Barber" <[email protected]> wrote in message
news:[email protected]...
> Is the top like this ???
>
> http://www.woodsmith.com/plans/armoire/
>
> If similar, I would use their(Woodsmith) method
> which requires NO bending....
>
> I bought a back copy of Woodsmith for another
> project and this armoire just happen to be in
> that issue. Very interesting method of making
> the curved top.
>
> Use multiple pieces and a router.
>
>
>
> Dick Snyder wrote:
>
>> My daughter has asked me to build a bookcase for her baby's nursery. She
>> saw something on-line that she likes. It has a curved top. I think I will
>> build the bookcase out of birch as it will be painted and I am thinking
>> of laminating 3 1/4" pieces of birch plywood to do the curved top.
>>
>> Here is my question. I know you have to build the lamination on a form
>> with a tighter radius than you want to end up with as the wood with
>> spring back a bit when you remove the clamps after gluing up the
>> lamination. Is there some guidance people can give me on how to figure
>> out that tighter radius??
>>
>> TIA.
>>
>> Dick Snyder

Is the top like this ???

http://www.woodsmith.com/plans/armoire/

If similar, I would use their(Woodsmith) method
which requires NO bending....

I bought a back copy of Woodsmith for another
project and this armoire just happen to be in
that issue. Very interesting method of making
the curved top.

Use multiple pieces and a router.



Dick Snyder wrote:

> My daughter has asked me to build a bookcase for her baby's nursery. She saw
> something on-line that she likes. It has a curved top. I think I will build
> the bookcase out of birch as it will be painted and I am thinking of
> laminating 3 1/4" pieces of birch plywood to do the curved top.
>
> Here is my question. I know you have to build the lamination on a form with
> a tighter radius than you want to end up with as the wood with spring back a
> bit when you remove the clamps after gluing up the lamination. Is there some
> guidance people can give me on how to figure out that tighter radius??
>
> TIA.
>
> Dick Snyder
>
>