There's a lot about wheelbuilding that's like being a chef. You pick good ingredients, and put them together according to a certain recipe in order to make a finished product. The getting from point A to point B is not always as straightforward as the recipe would have you believe, and is often where the really good chefs earn their stars.
We love Velocity rims. They're consistently straight and round, and their weights are consistent. One thing that kind of stinks about them (and this isn't limited to Velocity - we saw it with our previous rim supplier and we see it on basically all rims that don't have eyelets) is that spoke hole drillings are a bit raw. They don't finish the spoke holes beyond just drilling the hole.
It's a bit tough to see in the photo, but easy to feel with your hand - the spoke hole has a bit of extra jagged material around it. In manufacturing the rim, they drill the holes and then the rim gets anodized and see you later. Actually the brake track gets machined after anodizing, which is why the brake track is aluminum color and the inside of the hole is the color of black anodizing. The machining takes away the inconsistent layer that is left after the construction and anodizing process, and gives you very smooth braking (more on this in a bit).
That little extra bit of material around the spoke holes presents a couple of problems. First, the spoke nipples can bind on it during the build. This is more of our problem to overcome than a problem that your wheels should be affected by, but any obstacles that prevent the build process from going as smoothly as possible increases the chance for error. In the final throes of the build, when an eighth or even a sixteenth of a turn of the nipple is really significant, this comes into play.
If the hole's irregularity prevents the nipple from seating properly in the hole, then the path that the spoke takes from hub to rim won't be as straight as it should be, and over time this will cause issues. During the build process, we do a lot to optimize the spoke seating in the hub, and the spoke line, and the nipple seating (some of which I'm glad you don't get to see because it might look like we're trying to kill your new wheels before we even send them to you), but you'd be amazed how persistent a little shard of aluminum can be - but then of course it will give up just at the wrong time.
If that little shard of aluminum does sit in there forever, it will cause a little stress spike where it sits. This will either show up in the nipple being wedged against one side of the hole, or the nipple has a "princess and the pea" thing going on where one little spot has too much pressure. Over time, this can cause stress cracks in the spoke hole, which are of course terminal and very unwelcome.
So this little tool here, called a deburring tool, becomes pretty important. The blade, which is shaped like a hook, shaves a tiny small amount of material from the hole and leaves is clean and smooth.
Again, tough to see in a picture but easy to see and feel up close, a hole that's been deburred has no extra material around it and is nice and round and smooth. Perfect for a great wheel build.
(note that the inside of the hole is now silver)
Now, since we're looking at the brake track again, back to that. When the rim is built and the seam is joined together and then the rim is anodized and then machined, the brake track is crazy smooth, even at the joint. During the build, the rim is stressed as the spokes are tensioned and everything comes together. As this happens, the seam can get a tiny little bit out of whack. Neither you nor I own any measurement tools that could accurately measure the amount (and I own some pretty cool measuring tools), but when you hit the brakes and fell "thunkthunkthunkthunkthunkthunk" then you'll know it's there and you won't need to measure it to know. This doesn't affect the structure of the rim at all, and over a time of using the wheels it would wear into smoothness, but it would annoy you and tear up brake pads as that happened. So we take a bit of light grade sandpaper (200 grit) and lightly wet sand the brake track on the seam to make sure it's smooth.
Our goal is to deliver wheel builds that are as good as they can be straight out of the box and stay that way for as long as possible, and we use a lot of little tricks and techniques to help get there.