Hey dakkanauts, I just finished building my prototype movement tray, and I'm pretty pleased with it, so I thought I'd share.
Assuming you have the basic modelling supplies, they work out about a pound a pop if your doing an army or two. There is also a guide on snapguide if you prefer:
http://snp.gd/tbad4w
Supplies:
Sand
Superglue
White glue
Plate metal (I bought 0.9mm steel plate from a
uk eBay seller for £8 - enough to do 3000pts of high elves, and about 1500 of orcs and goblins)
Magnets (I bought 100 n40 6mmx2mm from eBay for about £6)
Old sprues
Putty (millionth was what I used)
Paint
Flock
a hacksaw or power tool for cutting the metal (the seller I spoke to can cut to size if required) pm me if you want details of the seller.
A needle file.
Method:
start by cutting some lengths of sprue to use as a border for the tray. File off any lumps and bumps. They don't have to be perfect.
Mark the footprint of the unit plus sprues on the steel:
Cut out the steel, watching you don't lose a finger. File off any sharp edges or burrs.
Scratch up the top surface of your steel - this will let the superglue and white glue get a decent grip. I just used a file in a circular motion.
Glue on your sprue borders. Take the opportunity to make sure everything fits at this stage, or you are going to be swearing later. File any excess sprue off at the corners.
Glue magnets into the bases of your unit. I used N40 strength 6mmx2mm. These are pretty strong, but there is a layer of sand to go between the steel and magnet, so this will reduce the strength.
Use modeling putty to 'dress' the sprues. Make sure you don't get any on the inside or bottom edges, or your models won't fit. You can go for a smooth look, but I've gone for 'muddy terrain'.
Pack modeling putty around the magnets in your models. This will help stop the magnet detaching from your model when removing it from the tray.
Paint the interior of the tray with white glue, and sprinkle fine sand onto it, taking care not to get on the sprue edge. Shake off excess. Once dry, give the whole piece a coat of glue to seal it.
Sorry a couple of the following images are sideways - I can't find an option to rotate. :/
Once everything has dried, base coat in a colour to match your model bases or whatever.
Wash, drybrush and flock to taste.
Test fit your unit, if you have done it right, all should fit snugly.
Hey presto. You can hold them upside down no problem, yet they are easy to remove once your soldiers get killed! Remember to give it a coat of varnish.
Hope someone finds it useful.
Eggs