I was doing an inventory of my armies the other day, and realized that my 15mm Alien Squad Leader project had stalled. I had a nearly complete Mechanoids army, but its opponent had evaporated when a pro-painter had a crisis, and I had never replaced it.
Furthermore, the Mechanoids were based 'the old way'. Years ago, I was a big fan of metal bases. I also had some ideas of basing most models individually, then using sabot bases to switch between rulesets and their basing requirements.
The first problem with metal bases are the sharp corners! They prick your fingers and catch in your terrain. Well, you can round the corners – and I've done that in the past – but the thin bases are still hard to pick up.
I've also learned, from experience, that metal bases sometimes corrode (even when you buy supposedly non-corroding metal bases!), so in the old days I would prime the bases on both sides to prevent corrosion.
However, the painted bases have a tendency to adhere to the flexible magnetic sheets lining my storage boxes. I had to use a blade to pry some of these stands loose, and you can see paint flecks on the sheet above.
So I decided it was time to rebase my Mechanoids, starting with the Assault Droids. (The models are called Heavy Tracked Automata by the manufacturer, but the troop type in the Alien Squad Leader v3.0 rules is Assault Droids, which falls in the Heavy Droids troop class.)
I'll be moving the droids to 50mm x 50mm bases, which are recommended for this ruleset.
I used a chisel to pry the models off their old bases.
Some of the glue and sand stuck to the model, so I carefully knocked the bits off.
The bases I'm using are 3mm-thick wooden bases from LITKO. I've sprayed them on both sides with black primer.
The rules give me the choice to mount up to four models per base. Above, I compare my options. A single model looks lonely; two models look crowded but threatening. I decide on two droids per base.
Some of you suggested the models would look better on dark bases, and I liked that idea. (Though it raises terrain issues!) So I am going to flock these bases with black sand.
You need a suitable glue for flocking. Standard white glue (i.e., Elmer's Glue) won't cut it. My glue pot says Graskleber from Noch, which really is the best product I've worked with for this purpose. But in reality, most of the glue in the pot currently is Aleene's Tacky Glue, slightly watered down. I used to buy the big containers at craft stores, but now I find it more practical to buy the tiny containers at Dollar Tree because the shelf life is not measured in gamer years. 
I use a wide brush to apply the glue, making sure to cover the entire surface. I avoid getting the glue too thick, because that can show when flock is applied. Any glue that gets on the base edges is wiped off with my finger.
I keep my black sand in a heavy-duty food storage container. You want a wide container that won't tip over easily, wide enough to accommodate your base sizes, with a secure lid to prevent spills. (Nightmare scenario: spilling sand on the floor of your painting room…) You want a smooth surface, so gently shake the container until the surface of the sand is flat.
Place the base, glue side first, into the sand and tap it a few times.
Now take the base out, tap it on the back a few times to get any loose sand to fall off. If there is sand on the base edges, brush it off with a finger. If there are any bare spots, sprinkle more sand over the base. I like to use black sand for urban bases, wasteland planet bases, and fantasy ruins.
Above are three finished bases. I will let them dry overnight, then give them a spray of clear matte to seal the sand in place.
The next day, the heavy droids get their first look at their new bases.
I use 'runny'-type superglue to glue the droids to their bases, because the glue should run into the sand and provide a bond from the base through the sand to the models.
Above, you can see the droids securely glued in place.
Well, no. The superglue didn't take, so I glued them down again, this time with thicker gap-filling superglue.
The hyper-observant among you will notice that the last two droids are not the same… As you may recall, I discovered a while ago that I had built the droids with their upper bodies facing the wrong direction! (Well, is it really wrong?) Since two of the droids had come loose over the years, I reversed their upper bodies to the 'correct' position.
The rebased Heavy Drones pose for the camera. Yes, they are 'old school' models, but they've still got that charm…
