This is a "notepad" for the fridge (though you could also use it, upside-down, placed on a table or desk). I designed it for rolls of paper that I have, which are:

• 2 1/4" (57cm) wide
• 2 5/8" (about 68cm) in diameter
• 1/2" (~8mm) diameter hole through the spool

Print these parts:

• main.stl (this is the main body of the thing; probably print with writing surface flat on build plate)
• cutter.stl (this is the paper cutter)
• cutter-post.stl X2 (or you can find some 4-5mm posts of some kind, like bamboo skewers, and glue/press them into the main body; they need to be guides to keep the cutter moving up and down in a fairly straight line; tolerance ~0.2mm). Update: The cutter probably doesn't need to move up and down at all; if it is fixed in place with a gap allowing the paper to slide under it, that seems to work OK.
• axle.stl (this goes through the center of the paper spool). Print horizontal, with supports and maybe a raft, for best results. Alternatively, just use a 6-8mm rod of some kind, and make it long enough that the rubber bands don't fall off the ends.
• arm.stl X2 (the arms connecting the axle that goes through the paper spool to the pivot points on the main body). 6/5/2019 Update: Arms now beefier around axle; they seemed a bit thin in first version.
• axle-cap.stl (these go on the ends of the axle so the rubber band doesn't fall off; you might need to heat them or glue them, depending on your printer setup; tolerance = 0).

Other stuff you'll need

• Four (4) rubber bands (to keep pressure on the cutter and on the spool)
• Two (2) M4 or M5 screws for the pivot on the spool arms.
• Six Nine (9) 8mm x 3mm neodymium (i.e., "strong") magnets. They should press into the feet (tolerance = 0) but, depending on your printer setup you might need to either heat the feet up a bit first (if the holes are too small) or use strong glue (if the holes are too big).

6/5/2019 Update: The paper roll is pretty heavy if it's full-size. Nine magnets is not quite enough for a slippery fridge (the unit slides down when you write on it) but seems just fine if the fridge is a little less slippery.

Assembly Instructions

(Or just look at the picture; you might be able to figure everything out from that)

Mount the cutter on the end of the main body, over the posts (or whatever you used as posts). Wrap one rubber band around the tabs on each side of the cutter and main body, to press the cutter down on the main body with a gentle pressure (trial and error will be needed to find the right pressure). Update: Rubber bands might not be needed at all. Just make sure there's a tiny space the paper can slide under the cutter.

Use M4/M5 screws to fix the arms to the pivot points in the main base part using the 5mm (i.e., smaller) holes in the arms.

Put the roll of paper on the axle in the round/cylinder-shaped area of the main body (see pic or diagram). Orient the roll so the paper feeds fairly smoothly (i.e., without a sharp almost 180-degree bend) out the slot in the body to the "top" (writing surface). Put the ends of the axle through the larger holes in the arms, then press caps on ends of axle to hold the roll in place.

Wrap a rubber band around the post on the main body and the matching cap on the end of the axle. Do the same on the other side of the paper spool.

Adjust

Adjust the rubber bands pressing the paper spool (via the axle) up into the main body, and those pressing the cutter down into the main body (Apparently this is optional). The goals of this are to (a) keep the paper roll from falling out or flopping around, (b) keep the cutter from falling off, and (c) add any pressure necessary so that the paper feeds nicely; that is, it's easy to pull it out of the end of the cutter without too much force required, but also so that the paper doesn't slide back into the roll or bend or bunch up on the writing surface. "Adjust" probably means wrapping the rubber bands around the posts/tabs multiple times or maybe getting different ones. Yes, this is 100% an exact science.

Pen Holder

Print as in the file (i.e., widest part of cone sort of pointing down, but "front" of bracket flat on build plate). Snap on (I hope) as shown in the image with the green pen holder in it. I designed the pen holder for a right-handed person (the holder is on the left of the rollpad), but it can be easily adapted for a left-handed person by mirroring the part (right-to-left) in Cura , Meshmixer, or your slicer/3D program of choice.

Note: pen holder v1 and v2 are identical except that v2 sticks out a bit more in the wide part of the "cone". IDK which will be more ergonomic/useful.