Are Dado's enough?

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Forum topic by Abn101mp posted 12-01-2016 02:16 PM 508 views 0 times favorited 6 replies Add to Favorites Watch
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51 posts in 736 days

12-01-2016 02:16 PM

I’m building a rather wider than normal book case. It is in 2 pieces, bottom in 2 ft high by 4 ft wide 11 in deep. Top is 4 ft high by 4 ft wide 8 in deep.
I have tight Dado’s. And I’m using 3/4 in pine.

Maybe I’m reaching back to my welding fabrication days, but I feel it needs support in the middle. But I don’t want it to look sectional. I suppose the customer isn’t going to be storing cinder blocks on the shelves, but the last thing I want is the shelfs to sag.
I was thinking a strip under the front and back going the width of the shelving but it would take away from the book space.
This is my first shelving unit for a customer this size. Any suggestions would be appreciated.

-- Dan,Mid-Maine

6 replies so far

View ChefHDAN's profile


1131 posts in 2994 days

#1 posted 12-01-2016 03:00 PM

I’d suggest using the Sag-u-Lator tool at this site

The issue will be load off set by the width of the front edging strip which is essentially an angle iron on the front of the shelf.

-- I've decided 1 mistake is really 2 opportunities to learn.. learn how to fix it... and learn how to not repeat it

View rwe2156's profile


3090 posts in 1625 days

#2 posted 12-01-2016 03:18 PM

You WILL get sagging in shelves that wide.

If you don’t want an edge strip, you can face glue 2 pieces of wood and plane down to 1 1/4”. Put an edge detail like an ogee or a bead will look good. Use the same 3/4 dados. A thicker shelf would look better for that width anyway (IMO).

Future reference, I’ve found a good general rule of thumb for is keep bookshelves at 30-32” wide. This would be for 3/4 plywood with a 1” hardwood front edge support. IMO solid pine is not much different than ply but you can consult that sagulator thing.

For thicker solid wood, I think you can go up to 40”.

-- Everything is a prototype thats why its one of a kind!!

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51 posts in 736 days

#3 posted 12-01-2016 03:26 PM

I put in the information in the “sagulator”. For an estimated 30 lbs centered weight at my measurements it is borderline.
I am wondering if I put a support strip I the back of the shelfs so it doesn’t interfere as much with space, but will give strength. It is the front that may become the issue.

-- Dan,Mid-Maine

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51 posts in 736 days

#4 posted 12-01-2016 03:30 PM

I have all of the pieces cut for the bottom. It is not assembled. So, that in mind, a divider that is dadoed in the middle of the shelf for each shelf that only is 1/2 or 3/4 the depth from the back is still an option. I am putting Birch backing on the unit anyway.

-- Dan,Mid-Maine

View bondogaposis's profile


4988 posts in 2496 days

#5 posted 12-01-2016 05:19 PM

Books are heavy, 4’ long shelves in 3/4 inch pine will definitely sag. Consider using thicker stock, like stair treads or adding stiffener strips to the front and back of the shelves.

-- Bondo Gaposis

View Abn101mp's profile


51 posts in 736 days

#6 posted 12-01-2016 09:04 PM

Thanks for all the tips and advice.
Since I have purchased all the lumber for this project and have the bottom section cut and dadoed, I have decided to run 1 1/2 in support strips under the shelfs front and back. I think this should do the trick and will definitely help keep things more square over time. Bottom shelfs will end up being 91/2 in high but I’m sure the customer will appreciate the strength. When u make the top, u will plan for more spacing with the support strips.
I’ll send out a pic when I get it completed.
Thanks again.

-- Dan,Mid-Maine

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