Time to gather all my development notes and techniques all into one post.
First a primer:
Magic: the Gathering is a convenient, abundant work material in some cases, despite the steep initial material costs. A card costs anywhere from $0.26 from a booster pack to $0.13 from a tournament pack. Found in many a gaming shop and teenager's closet, you can secure large quantities of "chaff" cards for little cost. I shall be dealing with non-foil cards, as I have yet to find a use for the foil "premium" cards.
If the idea of cutting up common and uncommon rarity cards scares you, lands are cheap and practically free from most shops and post-tournament gaming. I use anything that I deem "unplayable" or in gross excess, except lands, which I find useful. I particularly have a hatred for Centaur Veteran, from Torment.
Preparing the Cards:
Magic: the Gathering has a nice sheen/varnish to each card. It is slightly waterproof and resistant to some paints and glues. You'll need some sand paper, about the 80 grit range, to get rid of the coating. Once the card has some white showing, you've sanded enough. You may in some cases leave the surface on one side unsanded to take advantage of the smooth surface. Two unsanded surfaces have a drastically lower friction and wear rate than two sanded surfaces in planar shear. I take advantage of this property when making hinge and pin joints with Magic cards.
Elmer's glue is sufficient for working with Magic cards. Loc-tite can be used for emergency "quick drying" jobs or plastinating sections of Magic cards. That involves applying a thin layer of Loc-tite and letting it dry, forming a hard layer of glue on the surface. This is useful for increasing part thicknesses for joints. If you use Elmer's glue to form boards, they will require 2-4 days of drying time to fully stiffen. While they dry, they are relatively bendable and easy to cut.
I've experimentally determined a few ideal card thicknesses for use in construction. A minimum of 4 (four) cards is needed for a rigid structure of small size. For larger components like doll joints, 8 (eight) layers is recommended. Four layers conveniently is the thickness where you can still manage to cut the stack of cards with regular scissors. If you wish to cut cards with a tool, I would suggest cutting four layers at a time, gluing the stacks together, then work on the part as one solid piece for sanding/finishing purposes.
Material Properties- Thicknesses
A Magic card is approximately 0.012 inches thick, or 0.27mm. Depending on how well you apply glue (a thin coat spread evenly is recommended: excess will cause warping when drying), the thickness of the glue is negligible. With the sanded cards, I like to glue four cards together to form Magic: the Plywood. I keep a stack of these boards around for quick access. I do most of my work in increments of four cards for simplicity. Less variance in stock materials.
I have a chart to assist in gauging how much material I need to use for making a solid object.
With this, I can quickly gauge how many times I need to trace a part out before I achieve the required thickness. Keep in mind: Magic cards are not incompressible, nor are they static in thickness. You can easily thicken the edge of a 4-card board with aggressive Dremel sanding by up to 0.5mm. Significant, considering it's 1.2mm to start with. This occurs by delaminating the card's individual layers with frayed edges. This is why you should Dremel AFTER gluing laminates together.
Tooling and Cards
Now you have some 4-card boards, you're ready to make stuff. Treat these boards like wood. Really bad wood. Do not inhale the dust generated from cutting. The dust is a fine particulate.
For making holes, hole punches work for 2-3 layers deep before you encounter significant resistance. This allows you to make 1/4" and 1/8" holes with ease and precision. For other holes, you'll need a drill. Start off with a manual 1/16" drill to make a pilot hole. Don't bother making a hole in a material deeper than a couple millimeters by hand, otherwise it won't be perpendicular to the plane. A pilot hole is key to prevent edge fraying. With a Dremel, use your desired drill size and drill halfway through the material using the pilot hole as a guide, and repeat for the other side. Going straight through causes the other side to flare up like a volcano.
Material Properties: Stiffness
You may find yourself making something longer than the card is. In this case, put the necessary length of cards together and alternate the break between cards with a solid card, like a brick layer. Except, in this case, you want to alternate where the breaks are so they're not all stacked near each other. This weakens the structure significantly. Refer to the figure below for proper stacking.
Material Properties: Bend Radius
A 4-card board can be bent to some degree to form a curved surface. For smaller bend radii, you'll need to roll the card around a dowel first to prevent cracking. You can achieve small cylinders with Magic cards, but anything smaller than 1/4" is difficult. Magic cards are not recommended for tube making, unless the surface finish must be smooth as possible.
This post will be edited as necessary.