How to properly widen flashlight tube?

[johnny13oi]

Hey guys, I am gonna get my Ultrafire C2 soon and some Protected Ultrafire 18650s. I've been reading that the tube needs to be widened to accommodate these batteries. Is the process like attaching a sheet of sandpaper to a stick and attaching the stick to a drill and basically just run it for a while to widen? Are there any better ways? And if I were to do this, would this have any bad side effects, like would the inside corrode or lose it electrical conductivity over time? Sorry if these are dumb questions but I just wanted to make sure before doing something stupid.

 

[DonShock]

I just got done boring out a Nuwai ALX-352 that I recently purchased to let me use and AW protected 18650 cell. I used a 3/4" Forstner drill bit intended for woodworking. It fit perfectly inside the tailcap threads so it started nice and square and did a pretty good job. Lots of WD40 lubrication, gentle pressure on the drill press, and frequent clearing of the shavings made it go fairly quickly. However, the Nuwai had really thick walls so I knew I had plenty of room for error. If the C2 has thinner walls, getting the bit off center and blowing out the wall of the tube may be a concern.

 

[mmmflashlights]

Properly? With a lathe.

A drill press and a perfectly sized drill bit, while possible as DonShock described, would not be something that I would advise trying, unless you had a decent press and vice that would hold things perfectly in place and you had it centered very well. I would try something more along the lines of what you mention with sandpaper first, much lower risk of causing any damage to the tube that way, though it may take awhile depending on how much clearance you need.

Regarding corrosion or conductivity, don't worry about that, the tube is probably just bare aluminum on the inside already.