Bench seat strength question - Woodworking Talk - Woodworkers Forum
 
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post #1 of 11 Old 04-18-2012, 03:00 PM Thread Starter
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Bench seat strength question

First, as this is my first post here, allow me to give a bit of background: I am a self-taught hobbyist woodworker - that is, everything I know I have learned from TV Woodworking shows, found on the internet, or figured out for myself. I have been doing woodworking as a hobby for about three years now, primarily just furniture for my own use. I would describe my skill level as intermediate - My designs all seem to work, and look good enough to get praise from family and friends (not that that means much), but I run into plenty of problems getting them together that I have to work around, and the finished product has any number of flaws. I have signed up for this message board in the hope that it will be a good resource for filling in the many gaps in my knowledge.

On to the specific question for this post. I am currently working on building a love seat for my brother. As per his request, the seat itself measures 24" deep by 42" wide. I realize this is quite deep for a standard seat, but he likes to sit indian style, and wanted something deep enough to support his feet comfortably. The seat bottom is a slatted design, with the slats being birch, 3/4" x 1 1/2", spaced approximately 1" apart. The slats are mortised into rails measuring 2 1/2" tall by 1 1/8" thick, which in turn are mortised into legs measuring 3" x 1 1/8"

My concern is that I have no idea how much weight such a design would theoretically be capable of holding. Obviously I would want it to support at least two adults comfortably. Are the 3/4" boards thick enough to do this, given their 2' span, or do I need to look at reinforcing the design somehow, perhaps with a thicker cross beam under the slats or the like? I am attaching a png of the design I am using. Thanks for any feedback.
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post #2 of 11 Old 04-18-2012, 03:44 PM
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Originally Posted by ibrewster View Post
First, as this is my first post here, allow me to give a bit of background: I am a self-taught hobbyist woodworker - that is, everything I know I have learned from TV Woodworking shows, found on the internet, or figured out for myself.
Holy Toledo man, welcome home! There are many of us at various stages of your same journey along with some pretty unbelivable pros. Craftsmen used to learn with a mentor. Most of us don't have that these days and the other members here fill in that gap with a wealth of experience and knowledge. Welcome to the forum.
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post #3 of 11 Old 04-18-2012, 06:51 PM
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first impression

The stretcher or horizontal across the front/rear should be 1/2 again wider since you have all but removed the section by the mortises. 2X would be better. Those through tenons would look cool if you beveled the ends. I'll show what I did recently.

45 degree bevels/chamfers leaving a 1/8" flat:

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 #4 of 11 Old 04-18-2012, 07:11 PM Thread Starter
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The stretcher or horizontal across the front/rear should be 1/2 again wider since you have all but removed the section by the mortises. 2X would be better. Those through tenons would look cool if you beveled the ends. I'll show what I did recently.

45 degree bevels/chamfers leaving a 1/8" flat:
So your concern would be with the stretchers, not with the slats? That makes me feel better, as I can easily make them wider. It's also probably worth noting that the mortises for the slats aren't actually through mortises - that's just me being lazy with sketch up. I drew the slats the final depth of the seat and then slapped on the stretchers over them, rather than bothering to calculate (at that point) how long the slats actually needed to be. The mortises themselves are "only" about 3/4" deep. I'll have to try that technique with the arm attachments though - I am planning to through-mortise the legs into the arms. How did you cut the chamfers?
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post #5 of 11 Old 04-18-2012, 07:24 PM
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Originally Posted by ibrewster View Post

On to the specific question for this post. I am currently working on building a love seat for my brother. As per his request, the seat itself measures 24" deep by 42" wide. I realize this is quite deep for a standard seat, but he likes to sit indian style, and wanted something deep enough to support his feet comfortably. The seat bottom is a slatted design, with the slats being birch, 3/4" x 1 1/2", spaced approximately 1" apart. The slats are mortised into rails measuring 2 1/2" tall by 1 1/8" thick, which in turn are mortised into legs measuring 3" x 1 1/8"

My concern is that I have no idea how much weight such a design would theoretically be capable of holding. Obviously I would want it to support at least two adults comfortably. Are the 3/4" boards thick enough to do this, given their 2' span, or do I need to look at reinforcing the design somehow, perhaps with a thicker cross beam under the slats or the like? I am attaching a png of the design I am using. Thanks for any feedback.
My impression is that your design and dimensions for both overall size and pieces will be able to support two adults.






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post #6 of 11 Old 04-18-2012, 07:33 PM
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I used a router with a chamfer bit

I cleaned them up with a low angle plane and sanded them afterwards. Like this:
http://www.toolstoday.com/p-4954-cha...3_a_7c280_d_14

If you used a shouldered tenon, the mostise would be slightly smaller and the detail would be incredible looking. Are you going to use a cushion?

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 #7 of 11 Old 04-18-2012, 07:55 PM Thread Starter
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My impression is that your design and dimensions for both overall size and pieces will be able to support two adults.
Awesome, Thanks! I don't suppose there's some rule of thumb I can use in the future to determine this, is there? Or is it all just learn by experience?
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post #8 of 11 Old 04-18-2012, 07:59 PM Thread Starter
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Originally Posted by woodnthings View Post
I cleaned them up with a low angle plane and sanded them afterwards. Like this:
http://www.toolstoday.com/p-4954-cha...3_a_7c280_d_14

If you used a shouldered tenon, the mostise would be slightly smaller and the detail would be incredible looking. Are you going to use a cushion?
Gotcha. I'll give it a shot and see what happens. I was planning to get cushions for it, yes, although I don't know if my brother (who I'm actually making it for) will use them or not. I figure for something relatively small, it shouldn't cost too much extra. Besides, he's paying
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post #9 of 11 Old 04-18-2012, 08:16 PM
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Awesome, Thanks! I don't suppose there's some rule of thumb I can use in the future to determine this, is there? Or is it all just learn by experience?
Experience can be a great teacher.

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Originally Posted by ibrewster View Post
Gotcha. I'll give it a shot and see what happens. I was planning to get cushions for it, yes, although I don't know if my brother (who I'm actually making it for) will use them or not. I figure for something relatively small, it shouldn't cost too much extra. Besides, he's paying
Using cushions will lessen (disperse) the load to lesser direct stresses than just the slats.






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post #10 of 11 Old 05-07-2012, 12:12 PM Thread Starter
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If anyone is interested, I just finished up this project this weekend, and it was, in fact, plenty strong enough to hold me and my wife with nary a groan. Thanks for all the feedback. I posted a picture of it over in the project showcase forum
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post #11 of 11 Old 08-30-2012, 10:12 PM
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That turned out great!
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