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post #1 of 13 Old 05-19-2014, 11:47 PM Thread Starter
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Structural question

Am building some bookcases out of 15/16" Baltic birch plywood. They will be 8' tall and will not have face frames but will have backs. I will be cutting dadoes and gluing in some shelves while drilling holes for other floating shelves. The top and bottom will be stationary and I was thinking 2 more. My question is...for an 8' tall bookcase with no face frame, how many stationary shelves are needed??
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post #2 of 13 Old 05-20-2014, 12:17 AM
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not an expert but....

Your stationary shelves don't really hold the case together. The sides hold up the shelves not the other way around.

As long as you have a top and bottom then the case will be held square by the back since you have no face frame.

Hope this helps.

Bobby
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post #3 of 13 Old 05-20-2014, 01:00 AM
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Quote:
Originally Posted by Masterofnone View Post
Your stationary shelves don't really hold the case together. The sides hold up the shelves not the other way around.

As long as you have a top and bottom then the case will be held square by the back since you have no face frame.

Hope this helps.

Bobby
What he said!

Just make sure that the piece you use for the back is square at all 4 corners and across the diagonal and make the shelves conform to it and you should be good.

Stationary shelves are a mater of taste. I like one in the middle with the removable ones above and below. You may want more. IMO the important thing is spacing and getting each of them spaced correctly. You don't want a shelf in the middle, another a foot down from the top and a third just 8 inches below the middle shelf.

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post #4 of 13 Old 05-20-2014, 08:22 AM
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Without a faceframe there is the potential of the sides bowing outward if you load the cabinet down with something heavy. I think if you would put another stationary shelf about the middle it should hold it.
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post #5 of 13 Old 05-20-2014, 08:46 AM
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If the sides and top and bottom are machined with rabbets and assembled with glue/clamps, and fasteners if possible, that's your basic box. If the back edge is rabbeted for a square back that's a snug fit, and the cabinet is squared as it's installed, then that's a better box. I would use either one fixed shelf in the middle, or two, with proper spacing glued in dadoes, that will complete the box structure.

A single item of the parts isn't the determining factor of structural integrity, but rather, when all is in and done CONTRIBUTE to a better box. If I were making this cabinet, and using rabbets for the ends to accept the top and bottom, and installing one or two fixed shelves in dadoes, I would do all the rabbets and dadoes on the ends first. The top and bottom and the shelf or shelves would be cut the same length. Then rabbet the back edge of the ends and top and bottom for the back. Then cut the depth of the two fixed shelves to the same dimension as the depth of the ends from the front edge to the rabbet. Then do any sanding necessary to finish.

I would glue and clamp the parts to make the box all at once, checking for square. When those parts have dried, finish the cabinet and back separately. Then square the cabinet again and install the back.






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post #6 of 13 Old 05-20-2014, 09:20 AM
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Don't forget the toe kicks

If you have the ability, rabbet the back edges of the sides to accept the back. The back can either be 1/4" , 1/2" and nailed on OR 3/4" thick and rabbeted for the center shelves.... a bit difficult to get all the dadoes in the correct place.

The more secure the back, the stronger the cabinet will be. You also should not "over span" the shelves, 32" being a rough maximum for 3/4" shelving.

Don't forget to allow different height for various size books. Do not make the shelf spacing all the same. I would use 2 "fixed" shelves in a cabinet that is 8 ft tall. I would dado the sides to accept both shelves.
If you use pin holes for the shelf supports, then all the hole must be the same distance from the bottom or the shelves wont sit level. A temple would be best for that and they make drilling guides with the distances already drilled in.

OR you can use separate panels of material in between the shelves as spacers. These will act as "faux rabbets" to support them. This is what I do on larger cabinets sometimes since all you do is cut the panels the height you need for the shelves and place them in.

For a cabinet without face f aces you will need a means to conceal the plywood edges... either thin strips of the same material or the iron on edging.

Reply back with your questions and or progress.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 05-20-2014 at 10:50 AM. Reason: wrong terminology used
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post #7 of 13 Old 05-20-2014, 10:33 AM
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Quote:
Originally Posted by woodnthings View Post
The back can either be 1/4" , 1/2" and nailed on OR 3/4" thick and rabbeted for the center shelves.... a bit not difficult to get all the rabbets in the correct place.
I think that machining would be dadoes, not rabbets.

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I would use 2 "fixed" shelves in a cabinet that is 8 ft tall. I would rabbet the sides to accept both shelves.
Again, they would be dadoes, not rabbets.






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post #8 of 13 Old 05-20-2014, 10:47 AM
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yep, dadoes

Quote:
Originally Posted by cabinetman View Post
I think that machining would be dadoes, not rabbets.



Again, they would be dadoes, not rabbets.






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I hate it when wrong terms are used in the advice....

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #9 of 13 Old 05-20-2014, 11:02 AM
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Quote:
Originally Posted by woodnthings View Post
I hate it when wrong terms are used in the advice....
Just to clear the confusion for you, a dado is a groove within a field. A rabbet is a step machined on the edge.






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post #10 of 13 Old 05-20-2014, 10:51 PM Thread Starter
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Yep I will be cutting dados. Thanks for all advice. It turns out the bookcases won't be 8' tall, but will be 6.5' tall so I will do 3 fixed shelves with dadoes and a 1/2" thick back so it should be plenty strong.
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post #11 of 13 Old 05-20-2014, 11:51 PM
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Now that we got that cleared up, why are you leaving the plywood face exposed rather than making a face frame?

They have some really easy stuff these days to cover the plywood and comes in roles like tape and gets ironed onto the plywood. Gives the piece a more finished look than just exposed plywood edges.

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post #12 of 13 Old 05-21-2014, 12:58 AM Thread Starter
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I am not going to leave the plywood exposed. I am building these for my father and he just doesn't like the look of a face frame. I am going to either use the iron on edge banding or cut hardwood strips, haven't decided yet. Thanks for asking!
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post #13 of 13 Old 05-21-2014, 04:18 AM
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Quote:
Originally Posted by rookiewoodworker View Post
I am not going to leave the plywood exposed. I am building these for my father and he just doesn't like the look of a face frame. I am going to either use the iron on edge banding or cut hardwood strips, haven't decided yet. Thanks for asking!
Gotcha!

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