This time around I decided to go for bolt-on hemis: Bill's hemis are not removable which was a pain for painting. With Bill I used plastic balls which I cut in half with a junior hacksaw. This time I used Christmas decoration balls, which come in two halves which snap together, so they're not perfectly symmetrical.
Dalek hemis are not a complete hemisphere, but nearly a half-inch shorter, presumably because of an original push-through design. To get this effect with a bolt on hemi, I built a jig to cut them down.
The bench drill holds a hole saw, which has been covered in several layers of duct tape(!). This grips the hemi over a supporting disk which stops it collapsing as it is cut.
The disk is cut from the side by a large hacksaw, which is held in place by the slots visible at right (the hacksaw has been removed in the picture on the right for clarity).
To the left are the cut and uncut hemis for comparison. The hemi actually comes out 3mm less than the regulation 100mm diameter, is slightly visible if you look closely, but not much. I like it better than the full hemi. Each hemi needed a small amount of sanding on the bottom edge to clean it up.
To attach the hemis, some people glue bolts to the inside with epoxy glue. Some people fill the dome with insulation expanding foam. I cut 56 x 3½" wooden disks with a hole saw and put a nut and bolt through each. Each of these disks was then glued into a hemi with bathroom tile adhesive.
Here are the hemis bolted in place. I painted my hemis on the outside, because I didn't want the grip on the hemi dependent on a layer of spray paint applied with no primer, as I'd get by painting on the inside.
On the right below are two hemis. The top one is actually experimentally painted on the inside. The finish does look significantly better (it looks like black plastic rather than painted plastic when seen close up). I have recently noticed, though, that my experimental tugs on the bolt at the back have caused a little white line to appear where the disk is glued in. There may also be some slight shrinkage of the adhesive which is causing the paint to separate from the hemi. In the light of this, I think I'll continue to paint them on the outside.
The base is fairly straightforward, so I didn't say much about it last time. With Bill I used 2.5" castors, which turn out to be a bit small. Dirk has 4" castors. Because they're so tall they're mounted to blocks of wood. The separate base hangs from the bottom of these, so the bumper doesn't have to be so tall. A lot of dalek builders do this.
Another change I made is to use rotating castors at the front and fixed ones at the rear. This helps the dalek move in a straight line, as otherwise you tend to end up moving sideways a lot.