Hi, I build hot air engines and some times I use the rotary table, other times I just mark it out and chain drill, then clean it up with a file. When building with scrap you'v got to be a bit inventive. What is the flywheel for, a 3" aluminium one is very light. isc
As said its fairly easy if you have a rotary table or just print out a pattern and stick it to a wooden disc, drill out the corner radii and join up with a saw, then round the spokes with abrasive strips
As its just a pattern you could turn a rim and hub, drill six holes in each and then just glue in six dowels inserted from the outside for the spokes. At such a small size you don't really need a split pattern so quite easy
You may want to add a steel "rim" to give it a bit more weight or I have seen a groove turned in the cast rim which is filled with lead before applying a thinner steel "tyre"
Unless I was making a dozen or so, or I wanted to try casting for castings sake I would make it from solid, takes the same time more or less to make a pattern, unless as Jason says borrow an existing flywheel. isc
New guy posting in old thread. Here is my design for a built-up flywheel. The outer rim has an inside bead. The top of the spokes are machined with a radius to match the bead. The bottom of the spokes are rounded, but flat, to fit against the hub. The central hub is just a cylinder shape. The idea is to get the parts together in a tight fit and then silver solder. Although cast flywheels are cheap and plentiful, I prefer to make everything from built-up parts. Its a hobby and I like the challenge. Oddly enough, I don't want to take the easy path.
I traced the outline of the spoke on a brass flat, cut out the rough shape, and then marked the centerlines. I then used a round file to get the ellipsoidal shape. This was a quick and dirty "proof-of-concept" test, but I believe the above built up flywheel is viable. I would clamp all of the spokes into a rotating table to cut the groove on the end of all of them at the same time. This spoke does not have the groove on the top or the round on the bottom edge yet.
One method I used recently, I first made a hub, about 20mm dia x 20mm long with a 6mm bore, around the dia I bored and tapped six 5mm holes. I then made the rim 120mm x 10mm x 10mm, around which i drilled six 5mm holes. Then I cut six 5mm dia spokes, these were passed through the rim, then screwed into the hub, the outer end is retained in the rim with locktite.isc