I think i'm little late for the DIY Fidget Spinner thing, but i had this fantastic idea for quit some time and finally i got time to make it and to create a video and an Instructable about it.

The idea is to use a bicycle chain as the weight of the fidget spinner after making all the links tighter, so the shape of the fidget spinner can be played with and changed every time it's starts to get boring.

Step 1: Parts & Tools

For this project we gonna need this parts and tools:

Parts:

Bicycle chain (Cheap one).
Small ball bearing (I used a Z809 i had, it's 8x22x7 mm).
2 M8 Hex machine screws.

Tools:

Arc welder + 1.5mm electrode
Drill (or an angle grinder)+ wire wheel brush
Vise
Hammer
Small center punch
Long nose pliers
5min epoxy glue
Small screw driver
2 x M5 nuts
Ruler + marker
Small bucket full of acetone

Please remember Safety First, if get injured it won't be fun anymore, so use your safety gear and be careful

Step 2: Shortening the Bicycle Chain

I don't have a chain breaker so i used a center punch to extract the link pin, if you have tools for bike repairs this step should be even more easier.

Breaking the chain:

Count 20 outer plates or 40 link pins and mark the 40th link pin.
Open the vise a bit just enough for the link pin to get through.
Hold the bicycle chain and put the 20th plate over that small gap in the vise.
With a center punch and a hummer give the link pin a couple of strikes.

Relinking the chain:

Put the shortened chain on a flat surface.
Hold the link pin with the long nose pliers.
Give the link pin a couple of strikes until it's fully in

Step 3: Turning the Bicycle Chain Into a Modifiable Weight

Now that we have a short bicycle chain we need to make it stiffer so it hold its shape, to do that i got the idea of pressing the plates (outer and inner plates) on its rollers.

Put each M5 nut on one side of the link pins.
Put them in a vise and slowly start tightening the vise.
Take it out and see if it's tight enough and remember how much you tightened the vise (so you can repeat it for the other link pins).
Repeat 1 and 2 for every link pin (´ー｀)

Using a hammer in this step can speed it up significantly, but i found it to be not accurate as the vise.

Step 4: Welding the Chain to the Ball Bearing

I decided to weld the chain directly on the ball bearing to minimize the overall look, but a more practical way of doing this is using a piece of a tube that will be welded to the chain and then press fit the ball bearing inside it.
Epoxy also can be used instead but it wouldn't look that cool ᵔᴥᵔ

Welding the chain to the Ball Bearing:

Stretch and straighten the chain.
Put the ball bearing in its middle and mark it.
Clamp it in the vise (the vise will ensure that the plates stays parallel to each other)
Tack weld both outer plates to the bearing.
Flip it over and do the same to the other plates.
Unclamp it, bring the other middle plates to the ball bearing and clamp it back.
Tack weld them then do the same to the other outer plates.
Using a drill (or an angle grinder) with a wire wheel brush clean the welding.

Remember to not tighten the vise too much, that can shatter the ball bearing or deform it when it gets hot.

To prepare the fidget spinner for the assembly step we should remove the ball bearing's seals (in my case shields) to clean any grease in it an also from the chain. The easiest way i could think of to this at once is to use acetone.

With a small screw driver pry the seals and remove them with the long nose pliers (if it's shields poke a hole in them first).
Pour enough (acetone that will completely submerge the fidget spinner) in a bucket.
Put the fidget spinner in it, cover it and go to the next step.

Step 5: Making the Caps

For the caps i got the idea of using two hex machine screw heads to give it more of that industrial look.

So, i held the M7 machine screw in the vise then i measured and marked about 3 mm ( the ball bearing depth is 7 mm so i divided that depth between the two screws) and then i just cut them with a hacksaw.

I didn't protect the treads or deburr the cuts that will give the epoxy something to hold onto.