I'm making a twin-sized porch swing. Should I use 4 chains such that two of them connect together - thus resulting in only two from the ceiling, or use 4 chains and all 4 connect to the ceiling separately?
Without knowing the breaking point of the chains, expected loads, etc. it is difficult to answer this.– StevenJun 25, 2013 at 18:42
1Two chains, split into 4 will swing better, but then you have no redundancy at the support. 4 chains, bolted to separate supports will be safer.– Chris CudmoreJun 25, 2013 at 18:43
@Steven: I doubt the chain will be the failure point. It's the supports that worry me.– Chris CudmoreJun 25, 2013 at 18:44
The supporting hardware needs to be eye bolts that penetrate through the timber and are fastened on the top with a nut and a healthy washer. No lag eye bolts, they will pull out with resulting consternation, pain and injury. It's funny on AFV as long as no-one breaks their neck. Often, personally, it's a disaster.– Fiasco LabsJun 25, 2013 at 20:58
You also want something more than just chain hanging on an eyebolt. Most big box stores carry a special swing hook with a bushing installed to prevent metal to metal wear.– mikesJun 25, 2013 at 22:43
The chain configuration does not just affect the amount of support. It also controls the angle of the seat of the swing as it moves through its arc.
If you use a single hook on each end, the seat is always perpendicular to a line that extends from the center of the seat to the hook.
If you use two hooks on each end, the seat will track differently, depending on the length of the chain and the relative positioning of the hooks. One example is a parallel configuration.
Some configurations simply will not work well (e.g. if the space between the hooks is much wider than the space between the attachment points on the swing). Also, chains of different length will cause the seat angle to change (tip forward or backward).
As several comments point out, it is essential that whatever attachment system you use, the chains and the ceiling supports must be strong enough to hold the swing, the people and then the load must be multiplied by at least two or more to account for ther moving load.