Step 1: Go Get the Stuff Needed
If you want to make a pair like I did:
4 x 3/4" T's galvanized steel (Im using this so the cement has something to hold)
2 x 12" pipes with 3/4" thread
1 x rubber 6" x 3" pipe reduction
1 x optional plastidip (trying to get a rubber coated cement dumbbell)
Step 2: Attach Parts and Set Up
Just put the T's on each end of the threaded pipe, and suspend the pipe so the pipe sits perpendicular, about 1" from the bottom. See pic. I suspended it with pieces of styrofoam laying around and taped them. This is okay for this step, but once you have to do the other half of the dumbbell, obviously this would be to flimsy to hold the weight. I did a better setup in the next step.
Mix your cement in a bucket and start filling the rubber up. I adjusted the height of the rubber by putting the rubber on the styrofoam, almost no cement seeped through. It was ok. I wanted to go around it with a hot glue gun, but couldn't find it.
Once done, let it set overnight, cut the rubber reduction (see pic) and remove it. to reveal the cast.
Step 3: Do the Other Half of the Dumbbell
I used 2 concrete blocks (CMU's) and 2 broom sticks to suspend the half dumbbell at a perfect height, so the lower T is suspended 1" from the bottom. Since the rubber now has one cut in it, I taped all around to hold it well. This rubber also came with hose clamps on each end. Here again, pour the cement in and let is sit over night.
The result is pretty good. Nice finish. I did not do the step of the rubber Plastidip, as I did a test spray and didn't find it to be thick enough. Will do this on the cement once dry enough, after priming it.
I wanted to weigh the dumbbell, but my scale is type that needs to sense your two feet.
There are online calculators that can calculate the weight depending on the measurement of your shape. So you know how heavy it will get.
I will keep experimenting with this and make heavier ones