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  #1   Report Post  
blueman
 
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Default Shelf strength & thickness for 4ft adjustable bookcase span

I am building a built-in bookcase with a 48" shelf span and want to
make sure that I am designing the shelving system properly to support
the span with minimal deflection. The shelves need to hold heavy
textbooks.

- The sides and back of the bookcase are 3/4" cabinet-grade birch
plywood.
- Plan is to create 48"x12"x1" shelves by gluing together two sheets of
1/2" birch plywood.
- Shelves will be held in-place by a pair of 1/4" shelf pins at each
end. I plan to use sleeves to reinforce the shelf-pin holes.

I would like to avoid adding shelf-pins along the back because I don't
want visible holes. Also, I would prefer not to split the span since I
like the open look and don't want to have 2 narrow 2ft spans.

Questions:
1. Is this construction strong enough to support a 4 ft span loaded
with textbooks?
(I have had 3 foot span bookcases constructed from 3/4" material
and they seemed to hold)

2. Does anything else need to be done to stiffen the span? e.g.,
Thicker shelves? (I could use 3/4" to replace one or both of
the 1/2" pieces but then the shelves get heavier and
bulkier looking
Torsion box construction? (I could sandwich a 1/2" layer
between two 1/4" layers but this is added work and
added opportunity to mess up
Shelf pins along middle of back wall? (I really would like to
avoid the visible line of holes down the middle)

3. Will the 1/4" shelf pins with sleeves be strong enough to hold the
load? (e.g., should I use stronger or more shelf pins?)

Also, do the sleeves do much to strengthen the holes or am I just
as well off without them?

  #2   Report Post  
Duane Bozarth
 
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blueman wrote:

I am building a built-in bookcase with a 48" shelf span and want to
make sure that I am designing the shelving system properly to support
the span with minimal deflection. The shelves need to hold heavy
textbooks.

- The sides and back of the bookcase are 3/4" cabinet-grade birch
plywood.
- Plan is to create 48"x12"x1" shelves by gluing together two sheets of
1/2" birch plywood.
- Shelves will be held in-place by a pair of 1/4" shelf pins at each
end. I plan to use sleeves to reinforce the shelf-pin holes.

....

I personally think it will be marginal w/ ply. I'd make every attempt
to find solid lumber to make the shelves from. It would take some
clearance away, but you could use an edge on the shelves to gain some
extra stiffness if you could live w/o having close margins between tops
of books and next shelf. Overall, for a span over 3-ft, I'd really try
to put in a vertical center support if I could.

The 1/4" end pins are probably marginal and w/o the inserts I definitely
think they will tend to round if a 4-ft shelf is loaded to the maximum
possible. There are library systems that are more sturdy. Seems like
Woodworker Supply had some??? Or was it Woodworkers' Hardware in MN??? I
can't recall just now....

If it were me, I'd split it I think w/ single carcase, center support.
  #3   Report Post  
bob
 
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Why don't you mock up a shelf with some scrap, load it up, and test various
designs?


"blueman" wrote in message
...
I am building a built-in bookcase with a 48" shelf span and want to
make sure that I am designing the shelving system properly to support
the span with minimal deflection. The shelves need to hold heavy
textbooks.

- The sides and back of the bookcase are 3/4" cabinet-grade birch
plywood.
- Plan is to create 48"x12"x1" shelves by gluing together two sheets of
1/2" birch plywood.
- Shelves will be held in-place by a pair of 1/4" shelf pins at each
end. I plan to use sleeves to reinforce the shelf-pin holes.

I would like to avoid adding shelf-pins along the back because I don't
want visible holes. Also, I would prefer not to split the span since I
like the open look and don't want to have 2 narrow 2ft spans.

Questions:
1. Is this construction strong enough to support a 4 ft span loaded
with textbooks?
(I have had 3 foot span bookcases constructed from 3/4" material
and they seemed to hold)

2. Does anything else need to be done to stiffen the span? e.g.,
Thicker shelves? (I could use 3/4" to replace one or both of
the 1/2" pieces but then the shelves get heavier and
bulkier looking
Torsion box construction? (I could sandwich a 1/2" layer
between two 1/4" layers but this is added work and
added opportunity to mess up
Shelf pins along middle of back wall? (I really would like to
avoid the visible line of holes down the middle)

3. Will the 1/4" shelf pins with sleeves be strong enough to hold the
load? (e.g., should I use stronger or more shelf pins?)

Also, do the sleeves do much to strengthen the holes or am I just
as well off without them?



  #4   Report Post  
Mark Wells
 
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See http://www.woodbin.com/calcs/sagulator.htm

Gut tells me that two 1/2" sheets of ply glued together would be much
weaker than 1" thick ply.

Mark

  #5   Report Post  
Knothead
 
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You can offset the shelf sag and use 3/4 ply for the shelves if you wrap
them with a verticle grain face. Make a "frame" for the shelf out of 3/4" x
1 1/4" hardwood and rabbet in for the 3/4" plywood shelf. The shelves will
appear more "massive" but will actually be lighter and more ridgid. Even if
you stick to your 1/2" laminated idea any sort of verticle grain facing is
going to add to rigidity.

Knothead




  #6   Report Post  
Rumpty
 
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IF you want to use the two 1/2" plys, rout out matching 1/8" wide groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip into the
groves and glue up. This won't sag.

--

Rumpty

Radial Arm Saw Forum: http://forums.delphiforums.com/woodbutcher/start

- - - - - - - - - - - - - - - - - - - - -


"blueman" wrote in message
...
I am building a built-in bookcase with a 48" shelf span and want to
make sure that I am designing the shelving system properly to support
the span with minimal deflection. The shelves need to hold heavy
textbooks.

- The sides and back of the bookcase are 3/4" cabinet-grade birch
plywood.
- Plan is to create 48"x12"x1" shelves by gluing together two sheets of
1/2" birch plywood.
- Shelves will be held in-place by a pair of 1/4" shelf pins at each
end. I plan to use sleeves to reinforce the shelf-pin holes.

I would like to avoid adding shelf-pins along the back because I don't
want visible holes. Also, I would prefer not to split the span since I
like the open look and don't want to have 2 narrow 2ft spans.

Questions:
1. Is this construction strong enough to support a 4 ft span loaded
with textbooks?
(I have had 3 foot span bookcases constructed from 3/4" material
and they seemed to hold)

2. Does anything else need to be done to stiffen the span? e.g.,
Thicker shelves? (I could use 3/4" to replace one or both of
the 1/2" pieces but then the shelves get heavier and
bulkier looking
Torsion box construction? (I could sandwich a 1/2" layer
between two 1/4" layers but this is added work and
added opportunity to mess up
Shelf pins along middle of back wall? (I really would like to
avoid the visible line of holes down the middle)

3. Will the 1/4" shelf pins with sleeves be strong enough to hold the
load? (e.g., should I use stronger or more shelf pins?)

Also, do the sleeves do much to strengthen the holes or am I just
as well off without them?



  #7   Report Post  
firstjois
 
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[snip]
- Shelves will be held in-place by a pair of 1/4" shelf pins at each
end. I plan to use sleeves to reinforce the shelf-pin holes.

[snip]

Are the shelved attached to the case? If not, you could finish both sides
and flip the shelves occasionally. What bends one way will bend the other -
that sort of thing. I do this with closet top shelves of 1" pine that sag
over time. When flipped they straighten out and eventually sag the other
way.

Josie


  #8   Report Post  
Dave W
 
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Shelf design is a matter of how much deflection is acceptable (some
deflection is inevitable). The previous suggestion of making a simple
mockup is very sensible. If I had to guess, I would say that the two half
inch plywood shelves will have deflection noticable from across the
room......but that is only a guess.
Dave


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blueman
 
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"Rumpty" writes:
IF you want to use the two 1/2" plys, rout out matching 1/8" wide groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip into the
groves and glue up. This won't sag.

--

Rumpty


I like this idea...
Curious though why you pick 1/8" wide by 1/2" deep rather than the
other way -- i.e. rather than a wider narrow strip.

Also, where is a good place to get steel strips like that (I have seen
steel rod at the borgs but not strip)
  #10   Report Post  
blueman
 
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"Mark Wells" writes:
See http://www.woodbin.com/calcs/sagulator.htm

Gut tells me that two 1/2" sheets of ply glued together would be much
weaker than 1" thick ply.

Mark


Excuse my ignorance, but why would it be weaker?


  #11   Report Post  
blueman
 
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Duane Bozarth writes:
blueman wrote:

I am building a built-in bookcase with a 48" shelf span and want to
make sure that I am designing the shelving system properly to support
the span with minimal deflection. The shelves need to hold heavy
textbooks.

- The sides and back of the bookcase are 3/4" cabinet-grade birch
plywood.
- Plan is to create 48"x12"x1" shelves by gluing together two sheets of
1/2" birch plywood.
- Shelves will be held in-place by a pair of 1/4" shelf pins at each
end. I plan to use sleeves to reinforce the shelf-pin holes.

...

I personally think it will be marginal w/ ply. I'd make every attempt
to find solid lumber to make the shelves from.


What type of solid wood (without knotw) would you recommend that I
could buy in 12" width, 1" thickness, 4 (or 8) ft length without
breaking the bank?

I don't have a jointer so I would prefer not to have glue up a panel
using narrower stock.
  #12   Report Post  
Duane Bozarth
 
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blueman wrote:

.....
What type of solid wood (without knotw) would you recommend that I
could buy in 12" width, 1" thickness, 4 (or 8) ft length without
breaking the bank?

I don't have a jointer so I would prefer not to have glue up a panel
using narrower stock.


I'd assumed since you were building a sizable project you had stuff w/
which to do it...
  #13   Report Post  
Duane Bozarth
 
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blueman wrote:

"Rumpty" writes:
IF you want to use the two 1/2" plys, rout out matching 1/8" wide groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip into the
groves and glue up. This won't sag.

--

Rumpty


I like this idea...
Curious though why you pick 1/8" wide by 1/2" deep rather than the
other way -- i.e. rather than a wider narrow strip.


He's putting it on edge--the strong dimension. For this to work well
you will have to have the depth of the grooves at pretty close
tolerances.

Also, where is a good place to get steel strips like that (I have seen
steel rod at the borgs but not strip)


Most any hardware store will have 3-ft lengths, some may have longer.
Look in your phone book for steel suppliers in your area--some will deal
w/ individuals (for a price, but not any more than the exorbitant
piece-price at most retail outlets)....
  #14   Report Post  
Duane Bozarth
 
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alexy wrote:

Duane Bozarth wrote:

blueman wrote:

"Rumpty" writes:
IF you want to use the two 1/2" plys, rout out matching 1/8" wide groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip into the
groves and glue up. This won't sag.


He's putting it on edge--the strong dimension. For this to work well
you will have to have the depth of the grooves at pretty close
tolerances.


Actually, using epoxy to seat the steel should eliminate this concern,
shouldn't it?


Perhaps, but I don't think I'd count on it for long term...I suppose you
could fill the groove sufficiently, but my experience is that epoxy and
smooth metal surfaces tend to separate w/ age--or maybe I'm just
unlucky....
  #15   Report Post  
alexy
 
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Duane Bozarth wrote:

blueman wrote:

"Rumpty" writes:
IF you want to use the two 1/2" plys, rout out matching 1/8" wide groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip into the
groves and glue up. This won't sag.


He's putting it on edge--the strong dimension. For this to work well
you will have to have the depth of the grooves at pretty close
tolerances.


Actually, using epoxy to seat the steel should eliminate this concern,
shouldn't it?
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.


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bf
 
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Mark Wells wrote:
See http://www.woodbin.com/calcs/sagulator.htm

Gut tells me that two 1/2" sheets of ply glued together would be much
weaker than 1" thick ply.

Mark


I've read that a sheet of 3/4 ply is stronger than two 1/2 sheets glued
together. I can't prove it (lost the references), but it makes sense.

To the original poster. If it was me and I was dead set against having
a center support and it had to be 48" long.. I would use 3/4 ply, and
put a 1.5" strip of hardwood on the front. If you attach the shelves to
your 3/4 back, that will help too.

Another option is to just make the bookcase 32" wide. 3/4 ply
(particularly with a 1.5" edge) would definitely handle that span.

  #17   Report Post  
bf
 
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Just to clarify on my other post.. when I say to add a 1.5 inch of
hardwood to the front of the 3/4" shelf, I mean that the top 3/4" of
the edging will be fastened to the shelf, and the bottom 3/4" of the
edging will hang down. This helps resist sagging.

After you glue the hardwood to the ply, you can put a 1/4" roundover on
the on the hardwood edging. I do this because I think it looks nice.

  #18   Report Post  
RVH
 
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Andy Rae's book, The Complete Illustrated Guide to Furniture & Cabinet
Construction (from Taunton) has a good listing of span limits for
various materials. I doube your 1 inch plywood sandwich will be enough.
You might add hardwood edges that will not only cover the rough plywood
but add some stiffening.

RVH

  #19   Report Post  
alexy
 
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blueman wrote:

I am building a built-in bookcase with a 48" shelf span and want to
make sure that I am designing the shelving system properly to support
the span with minimal deflection. The shelves need to hold heavy
textbooks.

- The sides and back of the bookcase are 3/4" cabinet-grade birch
plywood.
- Plan is to create 48"x12"x1" shelves by gluing together two sheets of
1/2" birch plywood.
- Shelves will be held in-place by a pair of 1/4" shelf pins at each
end. I plan to use sleeves to reinforce the shelf-pin holes.

I would like to avoid adding shelf-pins along the back because I don't
want visible holes. Also, I would prefer not to split the span since I
like the open look and don't want to have 2 narrow 2ft spans.

Questions:
1. Is this construction strong enough to support a 4 ft span loaded
with textbooks?
(I have had 3 foot span bookcases constructed from 3/4" material
and they seemed to hold)

Probably strong enough, but probably not stiff enough. I.e., the
shelves probably will bend (objectionably, I'd guess) but not break.

2. Does anything else need to be done to stiffen the span?

I like Rumpty's idea of the imbedded steel stiffener. But other
possibilities might be worth mentioning.
Thicker shelves? (I could use 3/4" to replace one or both of
the 1/2" pieces but then the shelves get heavier and
bulkier looking
Torsion box construction? (I could sandwich a 1/2" layer
between two 1/4" layers but this is added work and
added opportunity to mess up

To add stiffness, You'd have to make it thicker, which adds to the
visual "weight", even if not to the mass.

A lip on the back, maybe both above and below the shelf to allow for
reversing as longer term sag occurs, would stiffen the shelf (though
not as much as front and back lips).

Shelf pins along middle of back wall? (I really would like to
avoid the visible line of holes down the middle)


Ask yourself (then answer realistically) how important the movability
of shelves is. Most are never moved, once set up to the owner's
liking. If that is the case, work with the side pins until you have
the shelves spaced like you want them, then attach cleats to the back
and sides under each shelf, and attach the shelves to the cleats.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.
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Duane Bozarth
 
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alexy wrote:
....
Ask yourself (then answer realistically) how important the movability
of shelves is. Most are never moved, once set up to the owner's
liking. If that is the case, work with the side pins until you have
the shelves spaced like you want them, then attach cleats to the back
and sides under each shelf, and attach the shelves to the cleats.


Actually, your idea suggests to me that if the shelves are to be heavily
loaded, the visibility of support pin holes in the back may not be such
a big issue, particularly if only the ones very close to the actual
height are drilled out instead of all possible. Then, a ledger strip
could be made which fit into those holes which would add quite a bit of
rigidity...


  #21   Report Post  
bridger
 
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blueman wrote:
I am building a built-in bookcase with a 48" shelf span and want to
make sure that I am designing the shelving system properly to support
the span with minimal deflection. The shelves need to hold heavy
textbooks.

- The sides and back of the bookcase are 3/4" cabinet-grade birch
plywood.


why 3/4" for the back? that will ad a lot of weight to the cabinet
without any real benefit. the back is mostly there to resist racking
forces (keeping it from becoming a parallelogram). 1/4" ply is more
than sufficient for that, although it will feel a bit hollow at 48"
wide. 1/2" backs will take care of that and make the case a lot easier
to handle.



- Plan is to create 48"x12"x1" shelves by gluing together two sheets of
1/2" birch plywood.


consider preloading the shelves when you glue them up. that is, glue
them so that they have a crown or upward curve equal to the amount that
they will sag once they are loaded.




- Shelves will be held in-place by a pair of 1/4" shelf pins at each
end. I plan to use sleeves to reinforce the shelf-pin holes.

I would like to avoid adding shelf-pins along the back because I don't
want visible holes. Also, I would prefer not to split the span since I
like the open look and don't want to have 2 narrow 2ft spans.


4' is a pretty long span for plywood shelves. given that you are
laminating 2 layers you will likely want to cover the edge anyway, so
make the edges wider than the shelf thickness by another inch or so.
it'll help avoid sag.





Questions:
1. Is this construction strong enough to support a 4 ft span loaded
with textbooks?
(I have had 3 foot span bookcases constructed from 3/4" material
and they seemed to hold)


some testing is in order.





2. Does anything else need to be done to stiffen the span? e.g.,
Thicker shelves? (I could use 3/4" to replace one or both of
the 1/2" pieces but then the shelves get heavier and
bulkier looking
Torsion box construction? (I could sandwich a 1/2" layer
between two 1/4" layers but this is added work and
added opportunity to mess up
Shelf pins along middle of back wall? (I really would like to
avoid the visible line of holes down the middle)


if you determine that a preloaded shelf laminated from 2 layers of 1/2"
BB is insufficient, a torsion box shelf or center pins may be in order.
if you go torsion box, consider 1/2" for the top layer, a 3/4" web and
1/4" for the bottom.

another approach would be to make the shelves fixed. then you could
rabbet the shelves into the sides and pin it solidly to the back. you
lose the adjustability, but you gain a lot of strength.



3. Will the 1/4" shelf pins with sleeves be strong enough to hold the
load? (e.g., should I use stronger or more shelf pins?)


the pins are plenty strong. where you may have failure is the wood
carcase that the pins are supported by. it's a lot of load on a 1/4"
wide section of wood. once the load reaches the crush point of the wood
fibers the hole elongates, the pin starts to shift, reducing the area
it has in contact with the wood, increasing the point load and failure
quickly follows.





Also, do the sleeves do much to strengthen the holes or am I just
as well off without them?


the sleeves increase the load area, and if you glue them in they help
resist shifting.

  #22   Report Post  
SonomaProducts.com
 
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Yes, use the sagulator to check this out. It can tell you if 1" ply
deflects more or less than various solid materials.

Other ideas.

1. You could use a stronger attachment at the ends. Have you ever seen
the old cabinet technique where you have a notched piece of molding at
the front and backs of the sides (kind of looks like dentil) and you
have a loose piece of wood say 3/4x3/4x12 that spans across a selected
set of notches and the shelf sits on that? Of course this assumes you
have a face frame to hide the ends of the shelves.

2. You can add a beam under the shelf. Say a 1" wide piece of 4/4 hard
maple turned on edge half way back. Pretty un-noticable but adds a huge
amount of strength.

3. If you use solid material you can go thicker but make it "look"
thinner by using an edge treatment. I like to use a panel raising bit
(without a back cutter) or a table edge bit (like a thumbnail). If I
use the pane bit I then round over the underside front edge too.

  #23   Report Post  
Bill Leonhardt
 
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"bf" wrote in message
oups.com...
Just to clarify on my other post.. when I say to add a 1.5 inch of
hardwood to the front of the 3/4" shelf, I mean that the top 3/4" of
the edging will be fastened to the shelf, and the bottom 3/4" of the
edging will hang down. This helps resist sagging.

After you glue the hardwood to the ply, you can put a 1/4" roundover on
the on the hardwood edging. I do this because I think it looks nice.


I like the suggestion to add a 1x2 (3/4x1-1/2) piece on edge to the shelf
front and I think it's a great way to go because:
1. It covers the plwood edge of the shelf.
2. It adds quite a bit of stiffening.
The part I don't like is that it stiffens the shelf in an asymmetrical way,
therefore as the shelf is loaded, you may encounter twist, etc.

It seems to me that if the books can clear a 1x2 on the shelf front
(assuming you don't insert them horizontally and rotate), they can clear a
1x2 on the shelf back as well. The second 1x2 will increase the stiffness
even more and the "C channel-like" shape will be loaded more uniformly.

Opinions???

Bill Leonhardt


  #24   Report Post  
adb
 
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Or even better yet...weigh a shelf full's worth of books. (ie, stack
textbooks until they're 48" high on the bathroom scale) That'll give
you an accurate weight to plug into the sagulator.
(http://www.woodbin.com/calcs/s agulator.htm )

  #25   Report Post  
Duane Bozarth
 
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adb wrote:

Or even better yet...weigh a shelf full's worth of books. (ie, stack
textbooks until they're 48" high on the bathroom scale) That'll give
you an accurate weight to plug into the sagulator.
(http://www.woodbin.com/calcs/s agulator.htm )


But, as was discussed in a thread here not long ago, the "sagulator" is
based on homogenous material and (to my surprise) the only plies that
add significantly in ply are those w/ longitudinal grain--the others
only add roughly 20% or so. So, one would have to look at the plywood
construction in order to estimate the proper dimensions to plug in.
Those would be only roughly 1/2 of the actual thickness so that the
two-1/2" sheets would be equivalent to only roughly 3/4", maybe...

I posted a link to the US Forestry Research site w/ a detailed paper --
a Google over the last week or so should find it.


  #26   Report Post  
Roland
 
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In article , says...
I am building a built-in bookcase with a 48" shelf span and want to
make sure that I am designing the shelving system properly to support
the span with minimal deflection. The shelves need to hold heavy
textbooks.

- The sides and back of the bookcase are 3/4" cabinet-grade birch
plywood.
- Plan is to create 48"x12"x1" shelves by gluing together two sheets of
1/2" birch plywood.
- Shelves will be held in-place by a pair of 1/4" shelf pins at each
end. I plan to use sleeves to reinforce the shelf-pin holes.

I would like to avoid adding shelf-pins along the back because I don't
want visible holes. Also, I would prefer not to split the span since I
like the open look and don't want to have 2 narrow 2ft spans.

Questions:
1. Is this construction strong enough to support a 4 ft span loaded
with textbooks?
(I have had 3 foot span bookcases constructed from 3/4" material
and they seemed to hold)

2. Does anything else need to be done to stiffen the span? e.g.,
Thicker shelves? (I could use 3/4" to replace one or both of
the 1/2" pieces but then the shelves get heavier and
bulkier looking
Torsion box construction? (I could sandwich a 1/2" layer
between two 1/4" layers but this is added work and
added opportunity to mess up
Shelf pins along middle of back wall? (I really would like to
avoid the visible line of holes down the middle)

3. Will the 1/4" shelf pins with sleeves be strong enough to hold the
load? (e.g., should I use stronger or more shelf pins?)

Also, do the sleeves do much to strengthen the holes or am I just
as well off without them?


another option is to rebate the back of the shelves into the backing of
the bookcase, you will lose the adjustability but you say you will be
using the bookcase for textbooks - a known height. rebate 1/8 of an inch
1nto say 1/2 inch ply backing? you should gain a lot of strength and
stiffness
  #27   Report Post  
dgadams
 
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On Wed, 13 Jul 2005 15:49:08 -0400, Bill Leonhardt wrote:


"bf" wrote in message
oups.com...
Just to clarify on my other post.. when I say to add a 1.5 inch of
hardwood to the front of the 3/4" shelf, I mean that the top 3/4" of
the edging will be fastened to the shelf, and the bottom 3/4" of the
edging will hang down. This helps resist sagging.

After you glue the hardwood to the ply, you can put a 1/4" roundover on
the on the hardwood edging. I do this because I think it looks nice.


I like the suggestion to add a 1x2 (3/4x1-1/2) piece on edge to the shelf
front and I think it's a great way to go because:
1. It covers the plwood edge of the shelf.
2. It adds quite a bit of stiffening.
The part I don't like is that it stiffens the shelf in an asymmetrical way,
therefore as the shelf is loaded, you may encounter twist, etc.

It seems to me that if the books can clear a 1x2 on the shelf front
(assuming you don't insert them horizontally and rotate), they can clear a
1x2 on the shelf back as well. The second 1x2 will increase the stiffness
even more and the "C channel-like" shape will be loaded more uniformly.

Opinions???

Bill Leonhardt


Bill is right on the money here. SWMBO bought a particle
board shelf with 40 inch wide shelves 5/8 inch thick.
It was my job to make it work. I added a 1.5 inch front
rail to all the shelves, then added a 1.5 inch stiffener
both front and back on each shelf. With a 1.5 inch face
frame all around the case painted up nice, the shelves all
look good and you don't really notice the stiffeners.
She loads this thing up with heavy notebooks and it
deflects just a bit (maybe 1/4 inch).

A good rail both front and back on each shelf and perhaps
some kind of stiffener would work. There are also shelf pins
that are inset into the shelf so they aren't seen. These
could be used along the back.

DGA

  #28   Report Post  
Rumpty
 
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Usually a 1/8 grove and a 1/8 strip of steel have a pretty good fit....if
you can find cold rolled strip (McMaster Carr) it's exactly 1/8, drop in
your epoxy and go.

We use this method for making the tables on the Radial arm saw. You could
also use a sheet of 3/4 ply and rout a 1/2 inch deep slot in the bottom and
glue in your strip, but you'll see the slots on the under side of the shelf.

--

Rumpty

Radial Arm Saw Forum: http://forums.delphiforums.com/woodbutcher/start

- - - - - - - - - - - - - - - - - - - - -


"Duane Bozarth" wrote in message
...
alexy wrote:

Duane Bozarth wrote:

blueman wrote:

"Rumpty" writes:
IF you want to use the two 1/2" plys, rout out matching 1/8" wide

groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip

into the
groves and glue up. This won't sag.


He's putting it on edge--the strong dimension. For this to work well
you will have to have the depth of the grooves at pretty close
tolerances.


Actually, using epoxy to seat the steel should eliminate this concern,
shouldn't it?


Perhaps, but I don't think I'd count on it for long term...I suppose you
could fill the groove sufficiently, but my experience is that epoxy and
smooth metal surfaces tend to separate w/ age--or maybe I'm just
unlucky....



  #29   Report Post  
Duane Bozarth
 
Posts: n/a
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Rumpty wrote:

Usually a 1/8 grove and a 1/8 strip of steel have a pretty good fit....if
you can find cold rolled strip (McMaster Carr) it's exactly 1/8, drop in
your epoxy and go.


....

It's the depth that's significant...
  #30   Report Post  
bf
 
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Bill Leonhardt wrote:

I like the suggestion to add a 1x2 (3/4x1-1/2) piece on edge to the shelf
front and I think it's a great way to go because:
1. It covers the plwood edge of the shelf.
2. It adds quite a bit of stiffening.
The part I don't like is that it stiffens the shelf in an asymmetrical way,
therefore as the shelf is loaded, you may encounter twist, etc.

It seems to me that if the books can clear a 1x2 on the shelf front
(assuming you don't insert them horizontally and rotate), they can clear a
1x2 on the shelf back as well. The second 1x2 will increase the stiffness
even more and the "C channel-like" shape will be loaded more uniformly.

Opinions???

Bill Leonhardt


Bill, since he was making the back out of 3/4 ply, I don't think a
second stiffener on the back is necessary, if he attaches the shelves
to the back. Of course, if he prefers adjustable shelves, I agree with
your idea.



  #31   Report Post  
Duane Bozarth
 
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bf wrote:
.....

Bill, since he was making the back out of 3/4 ply, I don't think a
second stiffener on the back is necessary, if he attaches the shelves
to the back. Of course, if he prefers adjustable shelves, I agree with
your idea.


But, OP did specifical want adjustable shelves and was looking to avoid
the holes in the back being obvious if he used pins there as well as the
ends...
  #32   Report Post  
alexy
 
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blueman wrote:

"Rumpty" writes:
IF you want to use the two 1/2" plys, rout out matching 1/8" wide groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip into the
groves and glue up. This won't sag.

--

Rumpty


I like this idea...
Curious though why you pick 1/8" wide by 1/2" deep rather than the
other way -- i.e. rather than a wider narrow strip.

Also, where is a good place to get steel strips like that (I have seen
steel rod at the borgs but not strip)


The HD near me has them, with rather unique pricing: 3' for $3.27 or
4' for $2.17! Both seem high to me, but for only a couple of pieces,
so what?
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.
  #33   Report Post  
Mike O.
 
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Default

On Wed, 13 Jul 2005 00:02:47 GMT, blueman wrote:

I am building a built-in bookcase with a 48" shelf span and want to
make sure that I am designing the shelving system properly to support
the span with minimal deflection. The shelves need to hold heavy
textbooks.
I would like to avoid adding shelf-pins along the back because I don't
want visible holes. Also, I would prefer not to split the span since I
like the open look and don't want to have 2 narrow 2ft spans.

Questions:
1. Is this construction strong enough to support a 4 ft span loaded
with textbooks?


We built a library for an attorney who wanted his bookcases as large
as possible with adjustable shelves. Our limit, because of sheet
goods, was 4' wide with shelves basically 46 1/2". We told him that
there was a possibility the shelves could sag but that we would try to
make them as strong as we could.
We ended up gluing 2 layers of 3/4" oak veneer core plywood together
then put a 1 1/2" x 3/4" routed oak face on both the front and the
back of the shelves. We told him that if the shelves did sag he could
just turn them over. The bookcases are full of big ass law books,
been there for ten years and he's never turned them over.

Mike O.
  #34   Report Post  
blueman
 
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Duane Bozarth writes:
blueman wrote:

....
What type of solid wood (without knotw) would you recommend that I
could buy in 12" width, 1" thickness, 4 (or 8) ft length without
breaking the bank?

I don't have a jointer so I would prefer not to have glue up a panel
using narrower stock.


I'd assumed since you were building a sizable project you had stuff w/
which to do it...


My wife already complains about my tool budget...
  #35   Report Post  
blueman
 
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"bridger" writes:

blueman wrote:
I am building a built-in bookcase with a 48" shelf span and want to
make sure that I am designing the shelving system properly to support
the span with minimal deflection. The shelves need to hold heavy
textbooks.

- The sides and back of the bookcase are 3/4" cabinet-grade birch
plywood.


why 3/4" for the back? that will ad a lot of weight to the cabinet
without any real benefit. the back is mostly there to resist racking
forces (keeping it from becoming a parallelogram). 1/4" ply is more
than sufficient for that, although it will feel a bit hollow at 48"
wide. 1/2" backs will take care of that and make the case a lot easier
to handle.


Well, it is a built-in, so I don't care much about moving it (other
than the first time). Plus, since cost of 3/4" is not very different
from a 1/4" sheet, I thought that the added stiffness to the back and
lack of hollowness would be worth it.

2. Does anything else need to be done to stiffen the span? e.g.,
Thicker shelves? (I could use 3/4" to replace one or both of
the 1/2" pieces but then the shelves get heavier and
bulkier looking
Torsion box construction? (I could sandwich a 1/2" layer
between two 1/4" layers but this is added work and
added opportunity to mess up
Shelf pins along middle of back wall? (I really would like to
avoid the visible line of holes down the middle)


if you determine that a preloaded shelf laminated from 2 layers of 1/2"
BB is insufficient, a torsion box shelf or center pins may be in order.
if you go torsion box, consider 1/2" for the top layer, a 3/4" web and
1/4" for the bottom.


Assuming that you are talking about 3 sheets of plywood sandwiched as
above, does a torsion box like that really work in the sense of being
stronger than just two 3/4" sandwiched together (both have the same
total width of 1.5")

another approach would be to make the shelves fixed. then you could
rabbet the shelves into the sides and pin it solidly to the back. you
lose the adjustability, but you gain a lot of strength.


Agreed, but I like the adjustability

3. Will the 1/4" shelf pins with sleeves be strong enough to hold the
load? (e.g., should I use stronger or more shelf pins?)


the pins are plenty strong. where you may have failure is the wood
carcase that the pins are supported by. it's a lot of load on a 1/4"
wide section of wood. once the load reaches the crush point of the wood
fibers the hole elongates, the pin starts to shift, reducing the area
it has in contact with the wood, increasing the point load and failure
quickly follows.





Also, do the sleeves do much to strengthen the holes or am I just
as well off without them?


the sleeves increase the load area, and if you glue them in they help
resist shifting.


thanks


  #36   Report Post  
blueman
 
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Roland writes:

another option is to rebate the back of the shelves into the backing of
the bookcase, you will lose the adjustability but you say you will be
using the bookcase for textbooks - a known height. rebate 1/8 of an inch
1nto say 1/2 inch ply backing? you should gain a lot of strength and
stiffness


Well, I was using the term "textbook" pretty loosely plus suprisingly
my textbooks do vary a fair bit in height
  #37   Report Post  
blueman
 
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"Rumpty" writes:
IF you want to use the two 1/2" plys, rout out matching 1/8" wide groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip into the
groves and glue up. This won't sag.


I think I will go with this idea since it seems to meet my criteria
best though it does entail additional work (but at least I get to play
with my new DEWALT DW618B3 router

My plan is to do the following.
1. Use two strips 1/8" x 1/2" with each strip aligned with the depth
of the shelf pin

I assume that "two is better than one" and that aligning with the
plane of the shelf pins should help transfer the weight directly
from the shelf pins to the steel supported part of the shelf (Is
this correct?)

Also, I assume that two strips spread out that way is better than
one larger central strip of the same total mass.

2. I plan to build a template for routing the groove out of a similar
4ft x 12" piece of plywood with slots routed out. Then I will use
a 1/8" straight cutting bit (is this right? I am new to the world
of routers)

3. One other thought I had. Would I be better off adding an additional
3rd row of shelf pins down the center.
i.e. even thought they are 1/4" and have glued-in sleeves is the
support itself marginal?

Please let me know whether I am barking up the right tree now.
Thanks
  #38   Report Post  
Patriarch
 
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blueman wrote in :

"Rumpty" writes:
IF you want to use the two 1/2" plys, rout out matching 1/8" wide groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip into the
groves and glue up. This won't sag.


I think I will go with this idea since it seems to meet my criteria
best though it does entail additional work (but at least I get to play
with my new DEWALT DW618B3 router


Seems to me that 1/8" is exactly the width of the kerf of a regular kerf
table saw blade. Big table. Nice fence. Excellent depth control. Good
chip collection.

Use your new router. You told you wife you needed it, right? ;-)

Patriarch
  #39   Report Post  
blueman
 
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Patriarch writes:
blueman wrote in :

"Rumpty" writes:
IF you want to use the two 1/2" plys, rout out matching 1/8" wide groves
1/4" deep in each ply sheet, epoxy in a 1/8' X 1/2" steel strip into the
groves and glue up. This won't sag.


I think I will go with this idea since it seems to meet my criteria
best though it does entail additional work (but at least I get to play
with my new DEWALT DW618B3 router


Seems to me that 1/8" is exactly the width of the kerf of a regular kerf
table saw blade. Big table. Nice fence. Excellent depth control. Good
chip collection.

Use your new router. You told you wife you needed it, right? ;-)


Absolutely -- how else do you save money by buying toys (I mean tools)?
  #40   Report Post  
 
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On Fri, 15 Jul 2005 05:30:38 GMT, blueman wrote:

if you determine that a preloaded shelf laminated from 2 layers of 1/2"
BB is insufficient, a torsion box shelf or center pins may be in order.
if you go torsion box, consider 1/2" for the top layer, a 3/4" web and
1/4" for the bottom.


Assuming that you are talking about 3 sheets of plywood sandwiched as
above, does a torsion box like that really work in the sense of being
stronger than just two 3/4" sandwiched together (both have the same
total width of 1.5")



the solid shelf will be slightly stronger. the torsion box shelf I was
picturing involves dimensional 1x as the interior webbing. the
advantages of this approach are weight, cost, ease of assembling a
prestressed panel.
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