I can’t help with anything CAD like, but if you just needed to have a proof of 3d concept model hashed out from like a sketch, I’m happy to lend a hand.
Draw the light in whatever you are comfortable with and then just post a .jpg. For CNC machining, if there are surfaces and contours, then an STL works nice as long as it is high quality. Other formats work well too but STL is common. For plans, about anything that will print is ok. I use Solidworks, Rhino, IronCad, & ArtCam mostly. There are demo versions of these but nothing free about them. The good part is that most files can be moved from program to program now. A lot of times, I use one for say the body of the light and another to add text or designs of some kind.
If its any help DraftSight is a free drawing program, from memory associated with solid works.
Interesting stuff TexasLumens. Is there a sweet spot price/size? Small hosts use less materials and time to mill but most of the same set up and large lights take more T&M but not much different amount of programming(or so I suppose). Would take less work to produce a dozen identical hosts?
Where do such draftspeople hang out. Stand nearby with a nice trit loaded flame tinted light and offer them some candy maybe? I see a need for a new sticky topic”3D host modeling shareware”.
LinusHofmann - thank you for the offer. I wish to get my feet wet in CAD design though. If the learning curve is anything like GIMP or Photoshop I have a way to go.
The light I have in mind is really quite simple though so I hope it will not take too long. I should ask ahead of time what are the desired specifications for a single 18650 reflector light. I know some of the specs are to be determined by myself but I would think there would be a few dimensions that are standard for an 18650 flashlight. The head OD will not be much larger than the body if that helps a little bit.
TexasLumens & MRsDNF - thank you for your suggestions too.
Right now I am going step by step so I still need to decide between the free CAD programmes I mentioned in post #19.
Depends entirely on reflector/optic choice. A straight tube light takes a maximum 20 mm reflector/optic. A bit larger fits p60. Then A8, M1, X6, and C8. Beyond that you get into heads 50mm or more. Don’t know if there’s any rhyme or reason to sizing.
Rufus, I suppose there is in most cases. If you purchase materials in small quantities then certainly, the little round tube lights for a P60 would hit that spot. I have to buy materials in fair sized quantities so the actual metal prices from a light that requires 2" stock over say 1.25" stock are negligible. Certainly there is some difference...but materials don't cost nearly as much as tooling, machines, time, software & etc.
You are correct on the programming and setup. It is all about the same on large & small lights. The exception is when customers want a lizard wrapped around the light...with eyeballs, toenails, and scales. Or like one I have in process now... some sort of critter I drew in Z-Brush (there is a program for ya!!! Whew!) that looks half bulldog and half....ummmm... ain't sure 
.... that is the head of the light. Those we call "Art lights" and frankly the hours are near endless.
I get in trouble for this a lot...but in my opinion, the materials for a scratch built custom flashlight are about 5% of the cost. There I go again!! I can hear the hail stones coming. 
Not true for modding...but for scratch building it's close! You make e think too much! Dan.
Wow, I wouldn’t mind seeing pics of these “art” lights
Linus, start right. The first step is not the flashy body you have in your head. That comes last. At least for me. I do it this way... MrsDNF, OL, and others may want to contribute here...they may know a better way.... BUT...
10 AM... Coffee....
1. The light design must meet the functionality requirements of the user. Side switch, tail switch, weapons mount, modes, in the weather or shelf queen. Pocket size, holster light, etc. 11 AM... more coffee
2. I lay out battery, LED, Driver, Reflector, lens, pill...custom made or commercial, switch, switch spacer, switch lock device, boot, etc (Don't forget the springs) Get out the calipers. Guessing will not work. This gives you a "minimum" material size you will need in diameter and length. Gotta have room for the internal chunks. For those starting a good P-60 hull might be easier. 12 PM lunch & iced tea..
2:30 PM... thinking of that scotch & water on the back patio....
3. Now, go to CAD and add your idea for a body leaving sufficient material for strength and durabliity. I seldom go to CAD until I have hand sketched (scribbles mostly) the light. It just gives me a better feel for what I am doing...others may not want to.
7 PM... ha! eyes are tired everything is a little blurry... gotta be eye strain!!! GOTTA BE!!! 
That is the basics of how I start. ... ME.... certainly as I said...others will do it differently and get good results. Hope this can help someone. Dan.
Here is the critter.... not finished...another lifetime and I'll have it ready! 
One more & I gotta get at it!!
I can’t even imagine doing that… wow.
And you haven’t even experienced the Zbrush UI yet 
It’s a unique experience to say the least 
Z-brush is a fantastic program if you survive the UI. Linus is right on target! I use a lot...A LOT... of cad/cam...software. Z-Brush beat me up for a year before I could open it up and just be comfortable working in it. Still have to put the fur on the critter... You can do that for me if you want to Linus.
They have a "Baby Z-Brush" that is free. It is called Sculptris. If you want some reason to just dive yourself nuts go play with it! You'll hate me! Ha! Linus made me do it!!!
Happy Easter To All! Dan.