ok fine I'm not normal about robots

This is a breakdown of my process, which I think is simple (if overexplained) and produces clean results. I recommend it, but the tools and methods may vary. I also encourage creativity when making cards. Even following my steps to the letter, you may find unique methods and strange compromises across boxes.

So first off, I use a disc cutter where I can because I don't trust myself to cut straight lines. This is not necessary, but it's good if you have one. Just be wary that the thickness of the box can cause the blade to shift the cardboard a little, so hold it tight and be careful with any small elements being cut out (sometimes it's worth switching to scissors or knife).

What most people probably should be doing, if they don't have something like that, is using a metal ruler to glide your knife across (metal is important. Your knife can cut into plastics and probably wood). I've also seen a physical outline guide used to make cards the right size, which might work as long as it isn't going to be damaged by the knife. Scissors often make jagged edges on the cardboard, but they can technically be used.

First thing I do is cut all the sides off the box. Cut cleanly, you might end up using something that touches an edge. You can also use the inside box as a scraps bin while you work.

But don't cut bits out just yet. Make sure you have a bit of a plan for what you want on the card first.

Obviously the front box art is usually the main attraction , so don't cut through that (although for bigger boxes, sometimes the side box art is the only thing that will fit).

Then keep an eye out for elements you want to include on the card - I try to never cut through gunpla grade logos, Bandai logos or names, since those are the 3 elements I use on mine. Look around your box to decide what you want on your card (and if you're like me and want consistency, make sure that all boxes will have them).

I also like to cut out spares, in case a box in the future doesn't have any good sized bits.

(Another good, but not necessary, idea is to have a good black marker on hand. Colouring across the sides of an element can make it look way cleaner on dark backgrounds. Some elements look kind of bad when there's white under them, so this can be very useful. It can even fix imperfections on the front face, like if a knife has scratched the front, or any edges that look ragged.

I probably wouldn't use it on lighter colours. It's also able to draw over some unwanted graphics that you can't crop out of the card, which I avoid as much as possible. Compromises.)

After I've cut out the elements, I move onto the main art for the card. I trace around the sides of a Pokémon card, using an erasable pen (Pokémon cards are a pretty standard size as far as I know). This is so I can move the card away to check if the border is where I want it in regards to the box art, and to let me erase the lines and try again if I'm not happy. Be careful with the pen, as even a moderate pressure with this type can dent the box and leave trenches, even when the ink is erased. You can alternatively use something else erasable like a pencil, (which may have a greater risk of leaving trenches when erased), or something that can be removed easily from the box (even some tape might work, just dont strip the art off). I highly recommend this step to reduce the likelihood of both misplacing your cut and misjudging the positioning of the art and elements.

Make sure you can fit your elements within the border without obstructing the art. Plan ahead, so that you don't accidentally cover up something important like the head with a name. No regrets that way. This is especially vital if you use a consistent layout across your cards. It's not always easy, sometimes you can be forced into an edge, or have some other limitation, so try to think carefully and creatively.

Then you cut out the border. Very simple.

I also happen to have this corner punch. You could just cut corners out manually, or you could leave it with a sharp corner, but the punch is easy. Note that you can't place elements flush with corners if you round them, but you can offset them (unless you super carefully cut the elements in the same way as the corner, which I wouldn't risk). Both sharp and rounded look good, it's just a matter of preference.

The final step is just sticking your elements on the card. I'm a sicko because I use blutack, since it let me adjust where I want things later down the road. I just haven't bothered to glue them yet.

If you're happy, just glue them. Probably something from a bottle, not a glue stick.

Once complete (and dried, if glued), you can protect your work a bit better with some card sleeves. I bought a big pack of penny sleeves for a dollar or two locally, so look around. You can also store and display your work with a card binder. Check the sleeve sizes for both, but it should be pretty standard.

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Also bonus fact, gqux boxes usually have a free extra card almost fully made on the sides of the boxes, they only need a Bandai logo. I actually usually cut out 2-3 cards from most boxes and put them at the back of my binder, just for fun. I cut a whole 5 out of the HG Messer box. You can also get a surprising amount of card art from the backgrounds of gunpla and 30mm.

Here's a video I stumbled into that shows the basics visually if you prefer

and this cool one with magnets