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Forum topic by Padriac Riley posted 12-19-2014 08:36 PM 1098 views 1 time favorited 21 replies Add to Favorites Watch
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Padriac Riley

36 posts in 733 days


12-19-2014 08:36 PM

I have some shelves a bit longer than normal in a wall sized built-in I’ll be starting after the holidays. In one area there will be a set of shelves running 42 1/2” and in another area there will be a 50 1/2” section. Both areas are 16” deep. The whole unit is being made from 3/4” (so 5/8” ish) Baltic Birch plywood including the back panels with solid Cherry facing. I am going to double up the plywood on the shelves as well as add something I saw taking down some ancient library shelves that hadn’t sagged over their 8’ in the 120 years they had been used.

My question is glue and clamping enough to join the plywood layers together or should I also add something like connector bolts counter bored in and doweled over after?


21 replies so far

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bigblockyeti

3666 posts in 1181 days


#1 posted 12-19-2014 09:00 PM

Given the surface area you’ll have at 16” deep and 3.5’ to over 4’ you should have tremendous strength in a clamped and glued joint without the need for anything else.

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Padriac Riley

36 posts in 733 days


#2 posted 12-19-2014 09:17 PM

That was my thought as well but I’ve never made shelves this wide before and I wanted to get some other opinions on it while plans can still easily be changed.

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runswithscissors

2177 posts in 1486 days


#3 posted 12-21-2014 05:34 AM

If, when you are laminating your plywood panels, you flex the centers up a little before gluing, the resultant slightly cambered lamination will be stiff and strong. Maybe 1/8” to 1/4” in the 42 or 50 inch widths. I think you could even get away with 2 layers of 1/2” Baltic birch by doing it that way.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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AlaskaGuy

2406 posts in 1770 days


#4 posted 12-21-2014 08:27 AM

Deleted

-- Alaskan's for Global warming!

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AlaskaGuy

2406 posts in 1770 days


#5 posted 12-21-2014 08:30 AM

Read the post pertaining to shelves

-- Alaskan's for Global warming!

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bobro

308 posts in 771 days


#6 posted 12-21-2014 08:48 AM



... as well as add something I saw taking down some ancient library shelves that hadn t sagged over their 8 in the 120 years they had been used…

You’ve got me curious! All the antique library shelving I can recall seeing is divvied up into what amounts to many small firm boxes, so it wouldn’t have occured to me that there’s additional support in some way- what is it?

-- Lao Ma: You are so full of anger and hatred. Xena: Everybody's gotta be full of something.

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TheWoodenOyster

1275 posts in 1396 days


#7 posted 12-21-2014 05:06 PM

You could also run a continuous dado in the back panel for support on the back edge. I know it depends on the construction of the case, but if the back is thick enough, you could do it. The other ideas above are great, especially putting a tiny bow into the shelves when laminating them. Seems like that would work really well.

I too am curious about the antique library shelving. Do tell!!!

-- The Wood Is Your Oyster

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Redoak49

1938 posts in 1449 days


#8 posted 12-21-2014 06:00 PM

I think that instead of doubling up the plywood, it would be better to add a front back and middle 2” wide lip. The middle one could be put in with a dado. This will create a stronger and lighter shelf than double plywood and probably at less cost. With a 50” wide shelf, if you put much weight on it you will get some sag.

There is a online program called the sagulator that is useful to give you some ideas for what to expect for different shelf configurations.

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johnstoneb

2143 posts in 1633 days


#9 posted 12-21-2014 06:18 PM

+1 Redoak49. If you run a 1.5 to 2” face frame that would be your front support and depending how thick your back is you could just support the middle with a pin or block. Run the sagulator 3/4 baltic birch is fairly strong and will support quite a bit.

-- Bruce, Boise, ID

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pjones46

986 posts in 2104 days


#10 posted 12-22-2014 03:15 AM

Here is something that may be of interest….the Sagulator.

-- Respectfully, Paul

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Padriac Riley

36 posts in 733 days


#11 posted 12-22-2014 10:36 PM

According to the Sagulator I’m more than fine. These will be book shelves loaded end to end with books and possibly a game system or stereo. Putting the dimensions in I’d have to have about 400 lb dead center or over 1300 lbs evenly distributed before sag became noticeable. I thought that odd so I pulled out my Pocket Ref and the math by hand and it appears to be right. I still can’t quite believe it but number rarely lie.

I guess I forgot to mention it in the original post that the shelves will be dadoed 1/4” into the 5/8” sides AND back, this is just standard for me when i build anything with fixed shelves.

@bobro I’ve helped take apart a few of the small town libraries around my area as the buildings became in desperate need of replacing. Twice for charity and twice I was being paid in all the salvage lumber I wanted. Maybe it was just one family of craftsman locally building these back in the day but in all four of the libraries I helped take down the 8’ foot shelves were built from two solid oak boards 12” with some type of wood glue or adhesive between the boards and very well concealed nails. The extra part that you couldn’t see until you got the ends of the shelves out of the cases was two 1/2” square steel tubes one in about an inch from the front of the shelf and another an inch in from the back that ran the entire length of the shelves and would have rested on the support at the shelf ends. They had cut a grove the whole length of the shelf half the depth in each half of the shelf sandwich and laid the steel in before final assembly. They probably chiseled it out. I will cheat and use a router.

Actually the very cool part for me personally was recognizing the name of the plant I was able to find stamped into the steel when I cut them out later at home as the steel plant my great grandfather and then my grandfather and then my father had worked at wayyyy back in the day.

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Redoak49

1938 posts in 1449 days


#12 posted 12-23-2014 01:03 PM

There is one thing that you really need to note when using the “Sagulator”. It only calculates the sag at the initial loading. It does not take into account the long term gradual creep of the shelves. We have all observed this with shelves.

Some shelves look fine when first installed and then in a year, there is significant sag in the shelves. I think that if you put books in side to side on the 50-1/2” shelf it will look fine to start and in a year you will start to notice a significant sag. with the 16” depth of the shelves, I think that you will see a sag on the front of the shelves even though they are dadoed both on the ends and back. If it were me, I would include a front edge strip of oak or some other hard wood.

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pjones46

986 posts in 2104 days


#13 posted 12-23-2014 04:35 PM

I have seen shelves reinforced something like below, I think this what you, Padriac, saw.

This was only used with cheaper materials as a stiffener or shelves which were constructed for extremely overloaded applications. Also used when shelves were floating. I’ve also seen what I call a decorative strong-back with opposing grain on the bottoms of the shelves.

-- Respectfully, Paul

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a1Jim

115202 posts in 3038 days


#14 posted 12-23-2014 04:55 PM

Just because the old bookshelves were doubled up plywood you really don’t need to double yours. Yours are only 42” long not 8’.I have a bookshelf given to me years ago with filled solid with woodworking books and the shelves are only supported by adjustable shelf pins. This book shelves span is 48” and is made out of MDF.
I routinely build book shelves the same way. The way your dadoing the shelves in makes them plenty strong,if you want overkill your build I would either connect your shelves to a face frame or glue a cleat to the bottom of the shelves.

-- http://artisticwoodstudio.com Custom furniture

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pjones46

986 posts in 2104 days


#15 posted 12-23-2014 11:35 PM

The problem with cleats is that they look tacky and if they are used without face frames, they really look tacky.

Normally when I make shelves that are fixed, I use glued sliding dovetail construction at each end of the shelves into the sides and dado the shelf into the back rather the cabinet has a face frame or not, but, I have jigs all set up to do this so it doesn’t take me that long to complete. Also, I only use solid wood for this type unless it is going to be painted.

It makes a difference based on application and what the client wishes vs builders ability, efficiency, and production techniques.

-- Respectfully, Paul

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