I accidentally discovered that a 10 mm nut and a 607 bearing both fit in a 19 mm hole, and that led me to build a fidget spinner quite easily using two nuts for weights.
Although I've really got nothing new to add to the science of fidget spinners, the construction of my spinner was so simple that I wanted to share it with those that might be interested.
Step 1: In General
I've built two of these spinners already, pictured here, one out of wood, and the other one out of plastic, but I want to focus on the plastic one. It is probably the easiest to make because suitable plastic is readily available in any shop that sells kitchen stuff: Plastic kitchen cutting boards (second picture).
I've use plastic cutting boards before in projects, and the construction of this spinner just proved again how useful they are. They're available in a wide variety of sizes, thicknesses and colours. They're also generally made of a bendy, durable kind of plastic that can be easily shaped with ordinary woodworking tools.
Regarding dimensions, I've found that for medium sized hands a spinner of 80 mm in length works well (third picture). The diameter of the bearing and bolts (19 mm) dictates a width of about 27 mm (last picture), and the thickness can be anything between 6 and 10 mm, I would say. The two spinners in the first picture are both around 7 mm thick.
Of course a triangular spinner is also possible, but for simplicity's sake I stayed with the simple rectangular shape for now.
Step 2: What You Need
You need a suitable piece of plastic, cutting board in our case, and of course a 607 bearing and two 10 mm nuts. Then also a 7 mm bolt and nut to fit through the bearing as a core to hold onto when spinning.
The only "specialised" tool you'll probably need is a 19 mm spade bit, shown in the first picture.
Step 3: Body Building
Easiest would have been to make the body of the spinner out of a single piece of 6 mm cutting board, but I also had 4 mm thick cutting boards of different colours and so decided to glue two pieces together for a two coloured spinner, about 8 mm thick.
I've found a hand saw, band saw or jig saw are the best to cut thinnish plastic like this. The plastic seems too bendy for cutting with a circular saw that are prone to kickback, like a mitre saw or table saw. It may be different for thicker plastic, but I'd rather not take any chances.
The first picture shows the two strips of 27 mm wide, but not yet cut to length.
Before I glued the two halves, now each cut to 80 mm x 27 mm, together, I drew the layout on one of the pieces (second picture). I also drilled (third picture) guide holes of 2 mm in the centre of the circles for the bearing and nuts, for when the spade bit is used later on. You can use a punch (fourth picture) to help drill the guide holes accurately.
Before gluing the two halves together, I roughened the inside faces with sandpaper for the glue to stick to. I also drilled four 5 mm holes opposite each other halfway through each half (sixth picture), hoping they'd form a kind of concealed rivet when filled with glue to help keep the bond intact.
In the third picture from the right the bonded piece of plastic can be seen. I used a two part epoxy glue, but I wonder if hot glue would also have worked. I think contact glue should also work if the inside faces of the two halves were roughened up enough.
After that the drilling of the three holes with the 19 mm spade bit is quite easy. Preferably a drill press should be used for the sake of accuracy, but if your aim is good any drill should do.
About the 10 mm nuts: Most that I've come across are 19 mm across at their widest part, but I've also seen some that is 18 mm across. In that case of course a 18 mm drill bit should be used for the two outer holes.
The last picture shows the plastic body with its three holes.
Step 4: Rounding Off
An easy way to improve the look of the spinner is to give the ends a bit of a curve.
Use a suitable round object like shown in the first picture to draw a curve on each end of the spinner. Then just remove the plastic along the line with sanding block or a sanding disc (second picture).
Step 5: Time to Bolt
The 607 bearing's inner diameter is 7 mm and thus needs a 7 mm bolt and nut to act as a core. This is a size not always found in one's parts bin, but your nearest hardware store will be able to help.
Cut the threaded part to 11 mm. I hope you have a better saw than the one I had to use!
Step 6: Assembly
Just push the bearing and two nuts into their respective holes, fit the centre core screw, and Bob's your uncle!
Of course it does not always work that way. If the bolts or bearing fit too loosely, just apply some glue. In the second picture you can see how I had to apply glue to the tips of the nuts to fix them securely in place.
In the case of the plastic spinner (first photo), the bearing did not fit securely, as the drill bit wandered a bit while drilling, and I had to stick a strip of masking tape around it for a more secure fit. Of course glue would also work.
Step 7: Balancing Act
Of course, chances are that a home made spinner's balance will be off.
If it is by a small amount, I remedy that by drilling a 2 mm hole near the end of the offending too light end, and fill it with a piece cut from a 2 mm thick nail. If you've got a 2.2 mm drill bit, fitting the pieces of nail with a smidgen of glue will be easier.
If one weight is not enough, add another one.
As you can see in the second picture, my wooden spinner needed two pieces of nail for near perfect balance.
For more serious imbalances, you can probably fill the hole of of the nut at the lighter end with something of appropriate weight.
Incidentally, one of those 10 x 1 mm round rare earth magnets for sale on Ebay or at Chinese stores (third picture) neatly fits onto a 10 mm nut (last picture), so that can also be used for balancing, if you happen to have any on hand.
Step 8: The Bearing
As spinner users well know, the factory grease has to be removed from a bearing for the best spinning experience.
I've found it is not necessary to open up the bearing to do this. I just submerge the bearing in mineral turpentine/white spirit/mineral spirit, slosh it about, and spin it often before submerging it again. After 20 minutes or so, the grease is gone, and the bearing spins quite freely.
Apparently no lubrication for ordinary bearings is necessary, because the load imposed on it during spinning is very low compared to the loads they were designed to endure. One DIY builder wrote he opens up the bearing, and coats just one of the balls with a tiny amount of light machine oil for some basic lubrication, which is too little to impede spinning.