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Old 09-02-2017, 03:43 PM   #61
wwhitney
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There's an issue with ripping 2x4s down to 2x3s that would be best to avoid. Namely, the grade of a piece of lumber depends on the size of knots and their location relative to the edges of the lumber. So if you rip a #2 2x4 down to 2.5" wide, you may not get a #2 2x3, because now a knot is right at the edge of the lumber.

So I suggest the following, in decreasing order of engineering preference:

1) Use a kiln dried 3x4 of the highets grade you can get, on the flat.
2) Use multiple kiln dried 2x3s of the highest grade you can get.
3) Get some select struct 2x4s, find the clearest portion you can, rip 1" off an edge, and put that edge facing up in the assembled beam.

Edit: (3) is not really a good option, because of the above.

Cheers, Wayne
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Old 09-02-2017, 03:53 PM   #62
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Thanks Wayne. You give me lots of good ideas. Here's one more for you, following your option 3. However, only rip 1/2" off for two of the boards and 1" off for the last. The plywood top can sit along the 2.5" board and then sit flush with the 3" board. That should give me a bit more cushion.
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Old 09-02-2017, 03:55 PM   #63
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Quote:
Originally Posted by Ali
What weight does the deflection calculator take into account? I mean a thousand pound load on that span is different than 300.
You raise a very good point that I overlooked.

The Deflecto use 50 psf. So if you enter a joist spacing of 16", it is using a load on the beam/joist of 66.67 plf. For a 5.25' long beam, that would be 350 lbs total.

Since this is a bench, I suggest designing for a 300 lb point load on the middle of the front edge of the bench. That load would be carried entirely by the beam you are building.

For a given total load, the deflection for a point load at midspan is greater than if the load were uniformly distributed over the full length of the beam (like the Deflecto calculates). The ratio is 1.6. That means you want to use the Deflecto with an equivalent total load of 480 lbs.

Since 16" joist spacing gives you a total load of 350 lbs, you need to increase the joist spacing by a factor of (480/350) = 1.37. That means you need to run the Deflecto with a joist spacing of 22" to handle the case of a 300 lb point load at the middle of your beam.

Cheers, Wayne
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Old 09-02-2017, 04:16 PM   #64
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P.S. If you want to keep this bench as thin as possible, you'd probably be best off designing it as a torsion box. I'm not familiar with the details of how to engineer that, however.

If you want to stick with conventional framing, I'd suggest accepting an extra 1/2" of height and using (3) 2x4s for the front beam, with one of them cut down in width to accept a 3/4" plywood top.

Cheers, Wayne
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Old 09-02-2017, 07:58 PM   #65
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What do you think?

Three 2x exactly 3" along the front. Two 2x exactly 3" along the back. 2x exactly 3" along the side. 6 addition rungs cut to 2.25" to hold the 3/4 ply. All of it sitting on 3 2x4 studs/posts on each front side and one along the back. Back nailed to wall.

anyone that could break this probably wouldn't fit through the shower door.

One more question for tonight. Should I attempt to pitch this contraption or just introduce the 3/8" pitch by adding thinset under the durock?
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Old 09-02-2017, 09:19 PM   #66
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I recommend you pitch the contraption.
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Old 09-02-2017, 09:26 PM   #67
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With your dry sense of humor, cx, I may be inclined to read that rather negatively.
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Old 09-02-2017, 09:30 PM   #68
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No humor intended this time. I recommend you slope the contraption to drain.

I also recommend you glue the plywood top well to the contraption. Not as good as plywood on the bottom, but it'll help some.

My opinion; worth price charged.
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Old 09-02-2017, 10:09 PM   #69
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My thoughts:

- Supporting the long edge of the plywood inlay would be stronger, I would cut down one each long dimension 2x member to 2-1/4" (nominal) on the front and the back, or at least rabbet them for half their width.

- With the ladder blocking, the orientation of the grain on the plywood is less important. If you don't support the long edges of the inlay, the plywood grain should be parallel to the long dimension of the contraption.

- I'm not sure I agree with the constraints of a) wood construction, b) only one side with plywood, and c) only 3" overall thickness. But if you support the long edges of the plywood, the design is about the best you'll do within those constraints, assuming proper fastening of all the individual members.

BTW, if you ripped your whole contraption to a 2" height, and could properly glue laminate 1/2" plywood to the top and bottom, you'd have a nice torsion box. That would probably be stronger, but I don't know how to analyze that.

Cheers, Wayne
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Old 09-02-2017, 10:44 PM   #70
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I've never called a seat a "contraption". But, I'm getting use to it.
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Old 09-02-2017, 11:38 PM   #71
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Thanks everyone.

Davy - we clearly don't frequent the same online content
Wayne - just for you ... a rabbet
CX - glue it is. Just hope I don't change my mind on the 17.25" height and 17" depth dimensions.
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Old 09-02-2017, 11:57 PM   #72
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Need to tidy things up a bit tomorrow but I'm calling it a night.
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Old 09-03-2017, 12:29 PM   #73
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Nice looking contraption you got there. :-) What did you use for stitch fastening the front and back beams?

Cheers, Wayne
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Old 09-03-2017, 12:48 PM   #74
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Nothing actually fastened yet. Was thinking nails, screws and glue. Was just kinda thinking through whether I had to attach it now or whether I could start on putting some durock up a 1' off the ground and my Kerdi so I can pitch the floor and fit my drain and do my water test.

Putting the bench in now would just make those other tasks more of a headache.

just need to mark exactly where it'll go given its as built dimensions and just make sure I don't put anything up that'll get in the way.

Im sure my next questions and pictures will be about Kerdi, mud and drains.
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Old 09-03-2017, 06:59 PM   #75
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So .... back to sloping the concrete floor. I get the whole slurry thing first and then making the mud itself dry and packing it well before shaping it. So for half the floor I can do that. The 2nd half of the floor as I'm sloping the floor towards the drain I'll be at 1/8" at best. 7'x5' shower area approximately.

There's some fortified mortar bed mixtures that may go down that low and I can definitely use thinset for the last 1/4"

Is it ok to mix compounds for the floor?

2nd. To get the slope right, I was thinking of cutting pieces of wood as guides and then removing them as the floor set up.

Im pretty sure I asked this question before but I still can't wrap my head around a good way to do it. Maybe I just need to get some materials and mess with it on a piece of scrap plywood. Yep. That's what I'll do. This bathroom grinds my basement progress to a halt.
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