Park Bench Quandry

My other half's grandmother finally had to move into an assisted facility. She is in the process of selling her home and is giving some things to the family. One item we got is a cast iron (aluminium?) and wood bench that looks very much like this one...
http://www.chinatraderonline.com/Files/Household/Furniture/Garden-Wood-and-Metal-Furniture/Park-Bench-21571168235.jpg
Most of the slats are gone but I salvaged one of each size for measurements in cutting news ones. However this bench has three straps underneath that screw into the wooden slats, one of which is missing. You can see the center one in the photo. The other two are one on each side of the iron sides (top of lower arc), go across about one third the length and up into a center slat, screwed in from the bottom.
Unfortunately one strap is missing. I was wondering how crucial are the straps to the bench structure. Can I do without one? Or can I run a rod across the length of the bottom of the bench instead?
The edges of the cast sides cover partially over the ends of the boards when put together, so I am assuming the straps are to pull the sides together. With about two thirds of the slats, and one strap, missing, the bench is very wobbly. I suspect full slats will help but I would like the bench to be as stable as possible.
Thanks for your input... `Casper
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With about two thirds of the slats, and one strap,

I can't fully follow your description but I assume the "straps" are diagion al to the slats and frames and are in different planes so they act as brace s. this is what will stop the structure from racking. So a straight rod acr oss the frames aligned with the slats won't do much for stability. Two rods crossing out of parallel to the slats connecting the frames will give you the opposing braces you really need for stability.
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wrote:

If you have a good one it would be fairly easy to use it to make a bending form, and then if you had access to torches it would be fairly easy to make one out of strap steel. It's importance probably depends on the flexibilty of the slats.
Mike M
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[This followup was posted to rec.woodworking and a copy was sent to the cited author.]
snipped-for-privacy@ghostmail.cc says...

I helped a friend assemble two new versions of this type of bench several years ago. The straps really need to screw into each slat. They bridge the flexibility of the slats from one to the next so as to stiffen up the bench. Without them the slats individually will flex and could potentially break if someone were to stand in the center of one.
Most of these benches (at least the lower cost ones) come with slats that are somewhere around 3/4 inch thick (or just under) and are quite flexible over the bench span. More expensive benches (and ones with greater than the usual span) come with slats that are more like 1.25 inches thick and are much stiffer - although the bench of that type that I assembled still had the center strap.
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On 10/10/2013 3:45 PM, Casper wrote:

The slats are a type of oak. Here it would be best to find white oak, it will need to be milled thin enough to fit in the cast iron "slots" in the end frames. The straps are to help keep the slats in plane with each other. Wood tends to warp, so if you have one slat warp up and the next one warp down, the seating can be uncomfortable. The little straps are just there to help this problem. Your bench will be fine without them, but can be added if there is a problem.
I suspect the Taiwan metric bolts have had better days. I would drill out the frames to accept SAE 1/4-20 carriage, get new bolts, buy Nylox type nuts. Stainless carriage bolts would be best.
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On 10/10/2013 3:45 PM, Casper wrote:

I have one of these benches on my front porch and have rebuilet 3 in the past using SS bolts and Ipe.
All 4 only had a single center strap running from the top top to the bottom of the front slats. This strap ties all the slats together so that all support the weight of the person/persons setting in on the bench.
FWIW I consider this style bench to be some what cruel to the person sitting on it. Very uncomfortable for more than brief periods of time.
If you are missing slats there is no doubt that the bench is wobbly. New benches are wobbly until you get all the slats installed and tighten the bolts.
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Bench problem solved. Had to use a grinder to remove most of the bolts and screws but managed to get 2 of each to stay whole. Managed to keep 3 strips of wood (two different sizes) that were mostly whole.
Cleaned the metal up and was deciding on paint when brother-in-law decided he wanted the bench for his new double level deck. So, it's now his project. Recommended he keep the straps and go with really good water resistant parts if he intends to leave it out all year with no cover. We'll see how he does. He's been finally getting into DiY home projects, this new deck his biggest yet. Certainly makes for more conversation during family gatherings.

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