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Old 05-21-2020, 12:40 PM   #1
Mini-Skoolie
 
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Safety of "wooden" seats

Hi all-- been lurking for a while and can't find anything on point, so here goes.

It seems that many folks build seats and benches then attach seatbelts to the floor/frame. So my question is this: a wooden bench as a seat seems to not be terribly safe, right? Even if bolted to the floor with automotive bolts it's still a wood frame. I'm thinking of just using existing benches but my wife doesn't love the look.

Thoughts? Insight?

Much appreciated.

-Tim
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Old 05-21-2020, 01:00 PM   #2
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Quote:
Originally Posted by trspaulding View Post
Hi all-- been lurking for a while and can't find anything on point, so here goes.

It seems that many folks build seats and benches then attach seatbelts to the floor/frame. So my question is this: a wooden bench as a seat seems to not be terribly safe, right? Even if bolted to the floor with automotive bolts it's still a wood frame. I'm thinking of just using existing benches but my wife doesn't love the look.

Thoughts? Insight?

Much appreciated.

-Tim
Hi Tim and welcome.
I'm dealing with the same issues now in my design stage.
For my front passenger seat I have reduced the wheelwell arch height and fabricated a steel cage to support the air ride seat I sourced from a semi truck.
That structure is bolted through six of the floor body frames. In regards to any additional passengers any motorhomes that I've been in just use the boxed dinette seats with lap belts. My thinking on this and the route I will be taking is for the dinette seating I will design that the lap belts will be bolted through the structural floor members. In an emergency stop or collision the energy should be absorbed by the belt not the box seat.
Just my thoughts.
Cheers
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Old 05-21-2020, 01:22 PM   #3
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It depends how it’s done, that is, it depends on how much steel is used to connect your wood. It can look like wood and have lots of wood in the construction, but have steel top to bottom.

And have you inspected the construction of a factory RV???
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Old 05-21-2020, 01:26 PM   #4
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And that being said, there’s a lot of engineering that goes into a seat, so what you make might not be safe in an accident.

But when I was a kid we rode on the over-cab bed looking out the window, so...
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Old 05-21-2020, 01:38 PM   #5
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Quote:
Originally Posted by trspaulding View Post
Hi all-- been lurking for a while and can't find anything on point, so here goes.

It seems that many folks build seats and benches then attach seatbelts to the floor/frame. So my question is this: a wooden bench as a seat seems to not be terribly safe, right? Even if bolted to the floor with automotive bolts it's still a wood frame. I'm thinking of just using existing benches but my wife doesn't love the look.

Thoughts? Insight?

Much appreciated.

-Tim
MH furniture is just sticks and staples.
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Old 05-21-2020, 02:01 PM   #6
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I have this notion that using the steel pipe frames from the school bus seats could be the foundation for sofas or benches which are then framed and clad with wood and fabric to be made comfortable without sacrificing the strength of steel. I would still send the seat belt mounts to the floor but if the concern is whether the wooden bench would maintain it's integrity in an impact or e-stop I think this would alleviate that concern.
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Old 05-21-2020, 04:42 PM   #7
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You may be interested in my discussion about DIY seatbelts here (https://www.skoolie.net/forums/f27/t...tml#post362523) and about DIY seats here (https://www.skoolie.net/forums/f27/t...tml#post364211).


I'm basing my research/info on https://shop4seats.com/rv-seating.html and various legal documentation for seatbelts. I spoke with a rep from shop4seats, and they said their seats are made of plywood but are also DOT tested and approved. Whatever that means.


I think the big picture is this: if you are in a crash and experience a sudden deceleration, the seats will only have a force equal to the deceleration times their mass, which is quite puny if made from 2x4s (relatively speaking). Meaning the way in which the wooden seats are attached to the bus only need to be strong enough to hold the seats down in the event of a sudden stop, so long as it's just the seat.



It's the seatbelts that need to be mounted in such a way that can hold a human passenger in (or an animal passenger I suppose). So I mounted my seatbelts directly to the bus frame (but not the chassis--see my post for why). This way, the seat is only responsible for itself, and thus can be made of plywood and secured with screws or throughbolted to the floor. Likewise, the seatbelt is responsible for the passenger, and it's the seatbelt--not the seat--that needs to have a strong installation. In fact it's actually outlined by law how the seat belts should be installed, but I couldn't find any corresponding laws for seats.



I would absolutely not install seatbelts to seats made of wood, that's offering no protection at all and you might as well just be standing.
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Old 05-21-2020, 07:32 PM   #8
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You may consider checking out some auto recyclers, maybe there's a "You-Pullit" near you. In my first bus, I used seats from a van, very comfortable, good solid frames and seat belts...seat belts properly anchored will be the most important part as far as safety is concerned.
Also, I don't know how long I would want to ride on a bus seat, they really weren't built for comfort.
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Old 05-21-2020, 08:14 PM   #9
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Ok. That makes sense.

Totally agree on having seatbelts anchored to frame NOT to the seat (unless it's an automotive seat that has the integrated seatbelt).

Thanks for the replies, folks!
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Old 05-21-2020, 08:57 PM   #10
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Quote:
Originally Posted by trspaulding View Post
Ok. That makes sense.

Totally agree on having seatbelts anchored to frame NOT to the seat (unless it's an automotive seat that has the integrated seatbelt).

Thanks for the replies, folks!
Just make sure that's to the bus body frames and not the chassis frame! The bodies can shear right off the frame in a collision and that would not be good to be strapped to the chassis.
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Old 05-21-2020, 10:44 PM   #11
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Steel is about 5 to 10 times stronger than wood, as a function of cross-sectional area:

Eastern White Pine
Tensile strength (parallel to the grain): 11,300 psi
Compressive strength (parallel): 4800 psi
Density: 21.77 pcf (pounds per cubic foot)

Mild Steel
Tensile strength: 63,800 psi
Compressive strength: (roughly the same as tensile)
Density: 490.75 pcf

So building a wooden chair or couch that is as strong as a bus seat would require using wooden members 10 times larger (in cross-sectional area). A bus seat uses 1" square tube with a 1/8" thickness (I think so, anyway - my seats were all stolen an I don't remember). Such a steel tube has a cross-sectional area of about 0.5 square inches, so a wooden beam with a 2.23" x 2.23" cross section (5 square inches) would be equally strong in compression (and twice as strong in tension).

Interestingly, the wood for this would weigh less than steel of the same strength (which is where the expression "wood is pound-for-pound stronger than steel" comes from). A 1-foot length of the 1" steel tube would be 0.00347222 cubic feet and 1.7 pounds, while a 1-foot length of 2.23" x 2.23" wood would be 0.0347 cubic feet and 0.76 pounds (less than half the weight of the steel).

In reality using wood would be a lot more complicated than this, since you have to consider how the wood is attached, along with irregularities in the wood, age and potential for rot etc. etc. (a steel tube also derives extra strength from its cross-sectional shape which you can't get from wood). I wouldn't want to do it, but it's not impossible. For sure, though, you would need to build much stronger wooden furniture than what you see in RVs.
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Old 05-21-2020, 10:51 PM   #12
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Quote:
Originally Posted by trspaulding View Post
I'm thinking of just using existing benches but my wife doesn't love the look.
Now that the safety end is addressed, I'll address the existing bench thought. When we first bought a bus, we set out on a spring break trip with nothing but a bed platform and 3 of the original bus seats. Man, are they uncomfortable for adults on long trips.
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Old 05-21-2020, 11:59 PM   #13
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if your seat belts are bolted to the bus body the tensile strength of any species of wood used or the cohesive value of the Gorrila Glue used and or the color of the staples you use should not be relevant. The energy is transferred through the belt to the body as you leave (leave being the operative word) the seat. The only energy impact on the seat should be you landing back on it. Build a solid box and get cruising!
Once again just my opinion and what I'm working with.
Cheers
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Old Today, 07:42 PM   #14
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I was considering cutting the backs of the bus seats and building wood around that as my bus seats were in handicap bus and had seat belts attached to them. But alas I said screw the belts.
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Old Today, 08:10 PM   #15
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Quote:
Originally Posted by trspaulding View Post
Ok. That makes sense.

Totally agree on having seatbelts anchored to frame NOT to the seat (unless it's an automotive seat that has the integrated seatbelt).

Thanks for the replies, folks!
I just spoke with a sales rep at shop4seats.com today to ask about the integrated seat belts. Unless you are replacing an integrated seat belt seat with another, they can't legally sell you one. You have to give a VIN # to prove that it is for that vehicle. Apparently it is highly regulated by DOT.
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