After failing to finish my flashlight last year I am coming back at it with a renewed vengeance. More info to follow shortly!
Reserved
Since it has almost been a month since I gave an update, I figured I should talk about my plans.
I have always dreamed of getting a Spy 007 or a FreLux Synergy, the wide side-by-side battery configuration appeals to me. While looking for inspiration for my build, I stumbled across CRX’s Rotary Flashlight, which sparked an idea in my mind. Why not make a side-by-side light with a rotary switch of my own? The larger footprint of the flashlight would allow for a larger, handbuilt PCB while still using a full-length battery (either 14500 or 18650).
I should be receiving my LED (Nichia 519a 3500K) and reflector in the very near future. Before I start building out the body of the light I want to finish the rotary switch module since it is the most experimental part of the build.
For the body of the light, I will be doing manual machining for the most part with small amounts of CNC machining and probably some 3d printing.
Lastly, the next major update will most likely be in two weeks’ time since I have 4 exams coming up but after that, I am clear till the end of the competition.
xqwerty151x, will we be able to witness your creation ? 
I hope everything is OK and that the exams went well 
Howdy, thanks to MascaratumB for asking about the thread. Long story short I won’t be able to complete my project, falling victim to single-point threading and school.
I joined an SEC competition team which has taken up almost all my free time. With the little time I had left between class work, my job, and the competition team; I decided to revisit my old design and to slightly edit it so I could use components I already had.
Unfortunately, while attempting to finish the tube and button cap, I messed up my single-point threading and scrapped the button cap. At this point, I have two exams next week that I need to study for in addition to a team meeting all evening tomorrow meaning I don’t have time to work in the machine shop again.
I have a few photos that I can share of what I had made so far but it is with great disappointment that I will not be able to finish my entry. Once I finish school I hope to have more time to work on projects like this.
Thanks and Gig’em
Using an endmill to create a flat-bottomed hold for the LED PCB, then I used a small boring bar to widen it.
A Perfect Fit! The wires were just from testing the LED previously.
Stainless steel tail cap. The original plan was to thread it into the Tube and then finish the end of it since I did not have enough to grab onto for the chamfer on the rear. Single Point threaded, but not well.
Pre-Drilled tube stock.
Post Drilling, pre-boring.
Post boring and threading but the two do not thread together. I belive it is due to stacking tolerances causing problems, tried to use thread files to clean up the threads but after about an hour of trying to fix it I decided to study for test instead.
Hey xqwerty151x, sorry to know that you won’t be able to finish it in time! However, don’t give up on it and when you have the tme, keep us posted 
I know exams and studying take us some time so I hope everything “shines” concerning that and then let it shine here as well
Good luck!
(and I wish I had that machine and some skills 
)
I also wish I could buy myself some machinery or have somewhere to put it. Luckily I’m a student worker at the engineering college’s machine shop so I have access to a bunch of expensive machines and have opportunities to learn to use them. Unforutanly I spend most of my time running a wire EDM and hole popper so I don’t get to practice manual machining much. That lathe in particular just had a new 3 Jaw chuck put on it so it was great to work with, some of the other equipment takes quite a bit of abuse with the mechanical engineers using them in labs.
Thanks for the update xqwerty151x.
I don’t know how well the instruction is where you’re at, but I’ll offer some quick advice about cutting threads:
Oftentimes the threads required in a scratch made flashlight are arbitrary, like .523”–32, or 18.3mm x .8mm, etc., and the dimensions and tolerances need to be calculated. This takes way too long if you do it with by the book formulas one by one, so a thread calculator is the practical way to go.
For calculating the thread dimensions, G-Wizard calculator is a good option. The “advanced thread calc” is a free component of the software and continues to work after the trial period ends. Clicking “save” and re-opening the generated thread calculator output in a spreadsheet can make it easier to see the data at a glance. Internal and External thread specs are generated separately.
Alternatively there is a spreadsheet calculator by Mark Cason (from this website) for inch threads, and a website based calculator for metric threads, just set it to “custom use” for arbitrary values.
Some thread calculators tell you what infeed amount to use with the compound rest set at 29 or 29.5 degrees, and this will get you close. Get close and measure.
Cut the external thread first. To measure the pitch diameter of the external thread you need to use thread wires (Tesa Brown & Sharpe 599-4816) and calipers or micrometer, which is the economical way to go, or use a thread micrometer. Thread micrometers are more affordable when purchased used. Thread wires work better with very fine threads than thread mics do, in my experience. Thread wires include a little chart with recommendations of which wire size to use for a given thread, and offer a formula for calculating the pitch diameter from your measurement. G-wizard and other calculators show thread wire related information, and arbitrary thread wire sizes can be used in the calculations.
For the internal thread, the proper thing to do is to make a Go-No-Go thread gage. Otherwise, for DIY projects you can just go by feel, cutting the internal thread so that your mating part threads in nicely, with a little extra clearance so that galling won’t be a problem, if you’re using materials that could gall. To make a Go-No-Go thread gage: this is a gage consisting of two external threads cut at the upper and lower tolerance limit of the pitch diameter of the internal thread. One should Go, the other should not, and then you know you’re within tolerance. What I usually do instead is make a single gage at or just below the mean tolerance value of the pitch diameter of the internal thread, and cut my internal thread so that this gage threads in but with no slop. The gages should ideally be made out of brass or bronze to prevent galling, or otherwise you should oil or grease the threads when testing, and don’t force it or you’re going to damage the gage. This mean tolerance gage approach allows me to make a single gage instead of two, and hit the mean tolerance very closely. Sometimes I will make all three gages: Go, No-Go, and the “Go-Without-Slop” mean tolerance gage.
Beyond all of that there is thread engagement / length and thread percentage to consider. Without getting into the weeds of bolt science / screw fastener design, (.pdf link) 6 complete threads is generally plenty. I like to have at least 2.5 to 3 complete threads on components like thin retaining rings, which requires rather fine threads to accomplish. A higher thread percentage value can be used to add some strength to a connection which has minimal thread engagement.
Thread percentage has to do with the form of the thread, how truncated the crest of the triangle is. If you’re drilling and tapping and your hole is oversized, the thread percentage will be reduced. Generally the thread percentage should be between 55% and 85. 75 is often used as a basis for recommended pilot hole sizes, for easy to tap materials. A reduced thread percentage, like 60%, is recommended for difficult to tap materials and deep hole tapping to reduce the likelihood of tap breakage. “Increasing the thread percentage from 60% to 72% in 1020 steel requires twice the torque, but with the same length of engagement, the strength of the thread only increases 5%.” Calculating thread percentage (.pdf link) is pretty simple and there are many calculators for this: 1, 2. Gage pins can be used to check your pilot hole diameter, and with this value you can do the calculation in reverse to determine the resulting thread percentage.
In general: pilot hole Size = Tap basic major diameter – pitch
Custom Inch: Drill Size = Basic major diameter – (0.01299 * desired % of thread / threads per inch)
Custom Metric: Drill Size (mm) = Basic major diameter – (desired % of thread * pitch(mm) / 76.98)
In reverse:
Inch: (Basic major diameter - measured hole size) / 0.01299 * TPI = thread percentage
Metric: (Basic major diameter - measured hole size) / pitch * 76.98 = thread percentage
Some more about thread engagement, mostly pertaining to nuts and bolts:
“Simply put, more thread engagement can result in higher tensile strength a joint. Tensile strength is the force required to pull something until it breaks or the capacity of that material to withstand that load. If a bolt is longer than needed to develop full tensile strength in a nut member, that excess material is wasted. On the flip side, if there is not enough bolt length engaged in a nut member, the bolt has a higher probability of stripping out before full tensile strength capability is achieved. Depending on the strength of the nut material, you need at least 1-1.5 bolt diameter engaged in the nut member to achieve optimum joint strength with a thread forming fastener. One factor that affects this is the nut material. Steel is a close to a 1-1.5 relationship, while softer material, like plastic will need more thread length engagement to achieve optimum joint strength.” (source)
“It is commonly known that the minimum recommended thread engagement to make a strong connection for a component with a tapped hole is approximately 1 times the nominal diameter in steel and 2 times the nominal diameter in aluminum. In many cases, (tapped hole in a softer material, special alloys, etc.) these values are not sufficient…” (source)
A bolt should extend 1 to 1.5 threads beyond the nut in order to get achieve full strength.
Notes:
-The basic major diameter of the thread is stated in the designation of the thread: 1/4”–20, 10mm x 1mm. The basic major diameter is 1/4” and 10mm in these examples.
-“form taps” require different hole sizes than cut taps.
That’s definitely some sage advice and I will defiantly keep it in mind if I end up single-point threading another project. I think if I end up finishing I might just program all of it in MasterCam and then run it on one of our CNC lathes whenever we have downtime.
In regards to the external threads, I did use thread wires, except I had to use the next size up since we were all out of the appropriately sized wire. I found a formula online but I probably used it wrong or just had my internal threads way off.
G-wizard has a good thread wire calculator built into the thread calc tab. You can enter arbitrary wire size values
The spreadsheet calculator will also let you enter an arbitrary thread wire size. You need to disable cell protection to edit the value of cell B27.
Also, just a small amount of cutting oil can make a big difference in your surface finishes.