Bookcases: stretchers needed? - Woodworking Talk - Woodworkers Forum
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post #1 of 8 Old 12-03-2019, 09:47 PM Thread Starter
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Bookcases: stretchers needed?

I’m building 3/4” plywood bookcases. Will be built in, lower units + cap; then upper units secured/sit atop the cap. Lower units are somewhat similar to kitchen cabinet construction but no toekick. Lower unit sizes: 26”h x 12”d and 30”,24”,18”widths. Glue/dado/dowel construction. Face frame will be attached covering the 4” gap between bottom shelf & floor. Are stretchers needed/recommended below bottom shelf in either front or in back, and/or below top of unit at back for structural integrity or to prevent racking? attached pic is one of lower units.
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post #2 of 8 Old 12-04-2019, 10:47 AM
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If the face frame is going to support the front edge of the lower shelf, what is going to support the front edge of the top shelf? With the ply you're using you will get sag over time. I would put a stretcher on it just to support the edge, but I'm relatively new to woodworking and have a tendency to overbuild things sometimes.
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post #3 of 8 Old 12-04-2019, 10:53 AM
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Unless you are going to put something very heavy on the shelves I would not use stretchers. 3/4: ply is quite sturdy all on its own.


You could debate using a stretcher on the 30" wide shelf. I would not. You definitely do not need on the ones of narrower width. For uniformity I would not use on any or use on all.



George
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post #4 of 8 Old 12-04-2019, 02:10 PM Thread Starter
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Quote:
Originally Posted by GeorgeC View Post
Unless you are going to put something very heavy on the shelves I would not use stretchers. 3/4: ply is quite sturdy all on its own.

You could debate using a stretcher on the 30" wide shelf. I would not. You definitely do not need on the ones of narrower width. For uniformity I would not use on any or use on all.

George
Thanks George! I was leaning toward no stretchers but being at the ‘now or never’ construction point thought it best to double check that I had not gone too far in other direction in my efforts to break/reduce my habit of overbuilding. I agree, the 30” widths are really the only concern, although uniformity is part of the picture. Thanks again!
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post #5 of 8 Old 12-04-2019, 02:24 PM Thread Starter
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Quote:
Originally Posted by Pistol View Post
If the face frame is going to support the front edge of the lower shelf, what is going to support the front edge of the top shelf? With the ply you're using you will get sag over time. I would put a stretcher on it just to support the edge, but I'm relatively new to woodworking and have a tendency to overbuild things sometimes.
Thanks Pistol. The hardwood face frame covers all the facing edges of the cabinet w/the lower rail wider than the stiles & top rail bc bottom shelf is ~4” above floor. A fellow overbuilder, I hear you! I’m trying to break/reduce the habit w/out compromising structural integrity.
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post #6 of 8 Old 12-04-2019, 02:39 PM
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The back and face frame stabilizes significantly shouldn't be an issue. The bottom rail and back will support the bottom shelf.

I agree 3/4 ply is sturdy, but not as much as you think. IME shelves >30" loaded with books will sag if unsupported. If you're doubting this take a piece of 3/4 ply 12" X 48 just supported at the ends, put a 10# weight in the middle and check it 24 hrs later & see if its sagged. Now imagine 40# of books on it 3 months later.



On shelves, I like to apply a 1 1/8 X 1 edge strip to the front edges with a 3/4" X 3/4 rabbet and chamfer the edge back to the glue line. It may seem like overkill but I think its worth the extra effort and on a shelf >30"loaded with books, it will never sag. If the shelf is wider than 30" I'll add second strip to the back edge similar to the front.


You've got to address the edge anyway, why not do it?

Last edited by DrRobert; 12-04-2019 at 02:45 PM.
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post #7 of 8 Old 12-04-2019, 09:01 PM Thread Starter
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The back and face frame stabilizes significantly shouldn't be an issue. The bottom rail and back will support the bottom shelf.

I agree 3/4 ply is sturdy, but not as much as you think. IME shelves >30" loaded with books will sag if unsupported. If you're doubting this take a piece of 3/4 ply 12" X 48 just supported at the ends, put a 10# weight in the middle and check it 24 hrs later & see if its sagged. Now imagine 40# of books on it 3 months later.

On shelves, I like to apply a 1 1/8 X 1 edge strip to the front edges with a 3/4" X 3/4 rabbet and chamfer the edge back to the glue line. It may seem like overkill but I think its worth the extra effort and on a shelf >30"loaded with books, it will never sag. If the shelf is wider than 30" I'll add second strip to the back edge similar to the front.

You've got to address the edge anyway, why not do it?

Thanks DrRobert. I agree the deflection rate of 3/4” plywood face (as opposed to edge) is significant over longer spans w/o an edge treatment, face frame, stretcher, etc to prevent.
My initial thought was to incl stretchers below bottom shelf front & back and at top back in addition to face frame. That seems like overkill. I’m thinking a stretcher at top back + corner bracing bottom back (under bottom shelf) might be good as an abundance of caution to help prevent deformation since these units + cap are the base for taller upper units. Thoughts?

I like the idea of rabbeting the edge treatment backs—thanks! Actual max shelf width here is 28.5” (30” easier to type). Shelves (adjustable) will have edge treatment 3/4”x1.5” front & back to ensure support heavy books & bc I prefer being able to turn shelves around since life invariably adds “character” to exposed finished edges sometimes, haha!
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post #8 of 8 Old 12-04-2019, 11:52 PM
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A little late, The back should prevent it from racking. Since the backs wont be seen bc its a built in, I secure the back to 3 of the 4 corners , take a square , square up the cabinent and shoot a screw in the 4th corner. Shoot other screws/nails around the back to fasten the back to the cabinet .

Then if necessary take a router with a flush trim bit to flush up the back
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