This page is part of the Cupcake CNC build sequence.
Cupcake CNC uses metric hardware for all its fasteners. Metric bolts are described in terms of the diameter of their shafts. For instance, an "M3" bolt is one with a shaft that is 3mm in diameter. Likewise, an M8 bolt has an 8mm shaft diameter. M3 nuts are nuts that fit M3 bolts.
The Cupcake CNC uses bolts of several lengths. They're described by the length of the bolt excluding the head. For example, a 10mm bolt is 10mm from the tip of the screw to the underside of the head. Sometimes you'll see a bolt described, for example, as M3x16. That means an M3 bolt with a length of 16mm, excluding the head.
Most of the nuts and bolts you'll use will be M3x16 - the Cupcake comes with 200 M3x16 nuts and bolts, but you'll end up with quite a few left over.
Bolt Together Action: The Nuts and Bolts
Nuts and bolts hold the MakerBot together. You put the nut in the slot, put the bolt in the hole and twist it with your fingers. Once you've got it hand tight, give it a small twist with the allen key to make sure it stays tight.
The Cupcake CNC uses several lengths of M3 bolt. The 16mm bolts are used to hold the outer frame together; the 10mm M3 bolts hold the inner X and Y stages together. The slots that accept the nuts on the X and Y stages have tighter tolerances than the ones on the outer frame. While this means that they tend to hold the nuts in place nicely, it also means that it can sometimes be tricky to fit the nuts in the slots. The variability of the M3 nuts we use is actually significant; if you're having trouble getting a nut into a slot, try rotating the nut a sixth of a turn and see if you have an easier time of it. If you're really stuck, try lightly sanding or filing the slot. Don't use too much force— you might break the slot!
MakerBots vibrate, so you're going to want to occasionally check the nuts and bolts and tighten them down if they loosen up. We haven't had this problem… but then again, these robots have only had a month or so to be alive at this writing… Hmm, I'm going to take a break and go tighten up all the nuts and bolts now.
The slots fit in pretty much perfectly. Those brown burn marks are "flame" marks. I like them so I left them instead of sanding them down.
Next Step: About Timing Belts