See post #82 here for the tail spring pictures: https://budgetlightforum.com/t/-/26078/82
Gosh, wouldn't it be neat if somebody could cut some threads in the battery tube, and make a screw-in plug to replace the press-fit stainless one?
Wait'n for the pics 
Ok, you have woken me up from my morning slumber with the words I have a lather and I’m not scared to use it. Or something along those lines. Yes its funny how most of the time the material your machining doesn’t know what tool is attacking it. Good stuff so far.
I’m not sure what you would do with a “lather”??? 
I built a jig to remove the tail plugs on my f6. It consists of only a bolt, three different sized washers and a nut. All I need to do is lightly turn the nut and the plug slides right out. The bolt pulls on the plug while the nut and washers push on the tube. Works very well! 
Buy, ya, why didn’t they just thread the thing?
I had read comfys thread a while back and followed hus suggestions when I reinstalled the spring. I didn’t have any copper disks(there’s been many times I wish I did, I should just suck it up and buy some), but I stripped a useless 20mm driver board, put a ring of solder all the way around it, connected the spring bypass wires to the ring of solder and jammed it all back in there… Seems to be working. Knock knock!
I knock the stainless plugs out with a deep well socket, short extension, and just whack it with a screwdriver handle.
The ID here is 0.786". Conveniently already has a relief at the bottom to stop the threads. I think I can find an o-ring the right size to fit in there after threads are cut do double duty, sealing and also centering the copper spring plate.
I have a spare pill & bezel to use as a thread gage. 1mm pitch, minor ID .801". Plan is to cut the internal threads to fit the male gage, then cut threads on the plug to fit the female threads. I don't care about proper thread profile or major/minor diameters according to Machinery's Handbook or anything, these two parts only have to fit each other, not standard parts from the hardware store.
Just use this stuff, works the same. Easy to cut to length. http://www.mcmaster.com/#standard-plastic-rods/=11jmoik
Beware, though... if you order 6 feet of 1/8", like I did, they will ship it UPS in a 6 foot long 4" cardboard tube and you will pay about $26 shipping for a $1.14 piece of plastic.
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awesome job!
For the first part - probably because the pics were all missing until a couple of months ago.
For the second part - you hit the nail on the head. Nobody is surprised to see comfychair producing results like this now that a mini-lathe is involved! If you take a look at some of comfychair’s older stuff you’ll see why.
Good work so far comfy.
I also have a rotary table/indexer thing now too. It may make an appearance here when it's time to make the new tail plug.
It makes stuff like these little thumbscrews (thumbnuts?) so easy it feels like cheating:
I am still looking for quality 24x1.5mm A/R lenses for these lights. I get in a really pissy mood for a few days after cutting and diamond-filing a C8 lens down to size. Yes, I have done that. No, I am not joking. I will pay a bounty to anyone who can locate a lens that's up to snuff.
There is a little bit of wiggle room for the OD, but the 22.61mm Mini-Mag lenses are too small to stay located on top of the front o-ring. The thickness is super ultra critical again because of the o-ring design. A thicker lens squishes the o-ring too much when the bezel is seated, thinner lens doesn't squish it enough to seal properly.
I’ve been ordering custom sized UCLp’s from Chris at flashlightlens.com. Also, plastic is much easier to work with if you have to trim them, but the thickness is fixed at 2.25 mm unfortunately.
The only way to make that work is to shave ~0.030" off the threaded part of the bezel. Sounds easy, but whatever stainless they used is unbelievably hard. I've shortened them before and the only thing that cuts it is fiber cutoff discs. Carbide doesn't work. It just melts the diamond off a diamond cutoff disc. If I had a surface grinder it'd be a snap, but unfortunately...
That is cheating. 
I am jealous. What rotary indexer did you acquire?
Hmm, couldn’t you remove 0.75mm from the face of the spacer and from the lip that the lens seats on?
Good question. I’d love to know as well.
A little toy 4": http://www.ebay.com/itm/291636636735
I made another adjustable adapter to mount the little toy 3" chuck that came with the little toy lathe. Loosen chuck mounting bolts, adjust the four #10-32 grub screws whichever way the test indicator says, tighten the bolts, and you get zero runout.
I would have to study it but my first reaction is that water could get down there around the OD of the o-ring, and bare aluminum and water don't mix well. Or maybe they mix too well... you know what I mean. The bezel isn't sealed to either the head or the lens so it's not waterproof until after the o-ring, everything before the o-ring is exposed.
So the indexing head is mounted on the cross slide?
Thanks for the link! The price is definitely right!
Hmm, I’m not certain that we are on the same page here.
Let’s ignore the optic for a moment… Assembling the head with a too-thick lens, the problem will be that the bezel ring will squish the o-ring too much, right? In the pictures it appears that the o-ring simply sits on a flat ledge. I’m proposing that you do a facing operation to reduce the height of that ledge by (1.5mm - 2.25mm = 0.75mm). In that case won’t the o-ring get squished exactly the right amount, as before?
I think I get it. You mean that if you do what I proposed, by the time water gets to the o-ring (by way of the threads) it will already be touching bare aluminum. I’m not sure that this is an issue for me, but maybe it is for you? Bare aluminum is pretty happy with water as far as I know….
Looks suspiciously like it’s mounted on an X/Y table in comfy’s drill press to me.
Yes, my poor very very confused drill press. It doesn't know what the fk is going on anymore.
It's now got a 2HP treadmill motor & controller, goes from around 30 RPM to a little shy of 11,000. And a reversing switch so it can do power tapping. I have a cheap digital caliper mounted to just the X axis on the table, I don't think I'm going to do a full-blown DRO on it. Might though. Depends how bored I get. It really needs a bigger table but I'm not sure it can handle the weight.