I know there are plenty of your A. R. types out there like me who wish BMI would do all the chassis prep work for us. Well, I don't know how to machine a slot for your battery tape to sit in, but I have found a way to get your battery slot bevels looking like a machine did them. They're actually not even bevels, but perfectly radiused copings for the battery to rest in!
I used my Mi3 chassis for this demo, but the concept applies universally.
Here we go . . .
Locate a grinding stone at your big box store similar to the one in the pictures. The important thing here is to match the sanding drum as closely as possible in diameter to the size of your cells. I have no idea where I bought the one in the pics, but I measured it for y'all. . . 1" diameter X 1" long.
Use a respirator and work in a well ventilated area to protect your lungs. This process will produce a lot of carbon fiber dust.
Set your chassis on a flat solid surface wtih a papertowel underneath (to catch the CF dust and allow easy disposal periodically). Keep several more on hand to use as you throw them away. I used 6; 1 per slot. Lay the drum in a battery slot (Make sure the countersunk holes on your chassis are facing down
) and begin sliding it back and forth from one end of the slot to the other. The picture shows how I found it the easiest to hold the drum. Be sure to complete the stroke to both ends to ensure you bevel the entire length evenly. Begin with light pressure to make sure the drum doesn't slide out and scratch the surrounding CF. As the bevel begins to form, increase the pressure to speed up the process. Just be careful to not go too far. It is much easier to get the CF off the chassis than it is to get it back on!
Periodically remove the sanding drum and brush away the dust to perform a test fit of an individual cell in the slot. You will be checking how far down into the chassis the battery is sitting. You obviously want the batteries flush with the bottom of your chassis, without hanging down.
Repeat steps 3 and 4 for the remaining battery slots.
Throw away all the contaminated materials, rinse off your grinding drum and chassis with water, and then take a cold shower; both to keep the CF dust from getting into your pores, and because your new chassis will be looking smokin!