My middle son has been making a variety of fidgets with his 3D printer. He particularly likes one he keeps in his pocket, a simple ball trapped in a groove. The only thing he does not like about it is its heft, too light. I will make him one of brass with plenty of heft.
After some consideration on ways to make this fidget with its trapped ball, I settled on the following. A 3" length of 3/4" brass round was cut from stock and faced on both ends. One end was center drilled, drilled up to a T drill, and reamed 3/8" to a depth of 1 3/8".
The rod was held in the milling vise and one side reduced by 0.125" creating a flat with 1/16" left between the new face and the hole. The milling was done with a 3/8" two flute end mill in 0.010" passes. The last pass of 0.005" was done very slowly producing a good finish. The first photo shows the milling in progress and the second the completed bottom face of the fidget.
A plug was made for the hole. A 3/4" length of 3/8" brass rod was cut off and held in the lathe chuck. A 5/16" ball end mill was held in the drill chuck mounted in the tailstock. The end mill was slowly fed into the brass rod as it was spinning producing a round pocket in the end of the rod. The remaining edge around the hole was faced and a short length of the rod was parted off at 1/4". The plug is shown below. The plug needs to be soldered in place, but this won't happen until the top has been mostly milled to depth and the purchased ball arrives and is put in place.
The top was milled similarly to the bottom done previously. About 1/64" of material was left between the top and the hole. No attempt was made to leave a nice finish as more material will be milled from the top after inserting the ball and plug. The sides were milled next as holding the part in a vise after inserting the ball would be a challenge. They were both milled about 0.05" deep leaving a corner with the top edge and a bit of the original brass round side at the bottom. Both were left with a finish similar to the bottom. The first picture below shows the milled bottom and the second the part after milling the sides.
One of the ten purchased 440 stainless steel hardened balls, shown below, was placed in the hole, but was too tight to roll freely, the point of this fidget. Ten minutes of sanding with 400 grit sandpaper rolled around a 1/4" rod gave a nice sliding fit, hampered only by air pressure. The plug was inserted and soldered into position as seen in the photo below. The part was left to cool.
The plugged end was finished with an end mill to get rid of the solder and tarnish. The top was milled down until an opening with ball was just noticed at the central end, as seen below. The end opposite that with the ball was then milled an additional 0.040" with the ball stuck in place. The ball was then moved to the plugged end of the device and the rest of the top was milled to the same depth.
The opening had quite a sharp edge, so the edges were trimmed flat with a 4 flute 3/16" end mill. All of the outside edges were heavily chamfered with a file. The entire fidget was sanded with 220, 320, 400, and 600 grit sandpaper. The ball moves nicely, but does get stuck in the plugged end. After working the ball back and forth the movement is very smooth.
