It’s easy to see the difference under magnification. 18350 short tube on the right.
The result being only about a 3/4 turn. Darn.
Hmm, looks like the threads on the right are the way they should be (symmetric) but the “right” threads on the left are asymmetric.
Possible to drag a grinding wheel (dremel-type) through the grooves to shave them down, but that’d be tedious. And no more ano so no more lockout, if that’s important.
I agree. I’m thinking one day I might be able to use this ‘wrong’ short tube elsewhere. Maybe with some modifications as you said. That particular thread pattern must be used somewhere in Sofirns line-up….cap-wise.
Oof…there’s a problem. lol. Hopefully they get you sorted with the new tube on the way. Little hard to say for sure but if I’m seeing what I think I’m seeing I wouldn’t bother attempting to alter the shape of either threading to try and get them to work. Sofirn is usually really good about fixing things and making it right, even if there’s some delay or trying to work around communication/language issues. Their reps (on aliexpress anyway) sometimes seem not to be very tech savvy or fully knowledgeable about the particulars of the lights, too, but they should make it right in the end. Glad you got the photo posting sorted!
Alright, so the short tubes’ a bust for now. Well we can still make fun with the 18650’s. I have to say I absolutely love the two-tone mash treatment, do it wherever possible and have never gone back.
One more.
From your picture of the tubes side by side; the left is a trapezoidal thread and the right is a square thread. The trap isn’t up to specs (it’s overcut: ie, the flanges aren’t equal to the groove).
I’ve taken the liberty of making a copy. Classic example of thread forms.
Woops! As Sidney Stratton said, the threads look to be different profiles. I wonder if someone simply used the wrong screw cutting form tip or if Sofirn changed thread profile spec at some point.
Which thread is correct? Thread on the right looks better to me because it’s evenly spaced between the root and crest. If that is the correct one then it may prove very difficult or impossible to get a 18350 tube to fit from Sofirn.
My threads on both tubes are similar to the one on the left. Both tubes works on my brand new SP40A and that 2700k tint is amazing!
This whole ordeal reminds me a bit of the first BLF A6 lights. If I remember correctly, the initial idea was that parts of the A6 should be legoable with the BLF-SE X6 EagleEye. But after a first component was made, it turned out to have a thread “of it’s own”. People suggested to trash that batch and manufacture it again, with correct threads. Finally the shop decided it would manufacture all parts with “new” (eg wrong) threads.
Just so looked over my SP40 and SC31 short tube. They are trapezoidal and are interchangeable. And can be reversed (front / back). These are not of these newer versions and were bought all at different times. The interchangeability is a nice feature.
Either Sofirn made a 18650 light variant that uses square threading and ended up in the wrong bin. Or the CNC operator called for the wrong program – and that should have been caught in QC.
Design engineering-wise, having interchangeable parts make for less component stocking. And most importantly, not have these issues of LEGO®. If they all too easily offered a replacement, Sofirn recognizes the issue.
On a side note, SpeedB will have learnt firsthand the difference between a trapezoidal thread (30º) and a square thread (90º). All too often people use the designations loosely.
Yes, the 18350 tube on the right has the incorrect thread profile. I think. It will not accept the tailcap from the kit so is useless. Thanks to Sofirn the replacement/correct tube has already made its way to L.A. and is en route to La.
Indeed. Ordered the SP40 for use in 18350 tube short form. More so for its interchangeability with the SC31 Pro, which is the light I was really pining for.
Sidney Stratton: On a side note, SpeedB will have learnt firsthand the difference between a trapezoidal thread (30º) and a square thread (90º). All too often people use the designations loosely.
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Regarding the SP40, there’s yet more discussion to be had regarding thread differences that you pointed out. As we know the ‘wrong’ square cut threads from the ‘incorrect’ 18350 short tube will not screw into/accept the SP40 tailcap. Interestingly though, the tube will screw into/accept the SP40 head! So I’ve also learned that the receiving/female threads are cut to accept either thread profile. The trap cut on 18650 tube and square cut on the 18350 tube both display a similar fit/mesh/play into the SP40 head. Maaaaybe a slightly better fit with the 18350? Overall thicker threads may account for this. On and on we go: so the threads are identical on both sides of either tube, but obviously the threads on the tailcap and the head are different. Whew.
Interesting that the square threads of the 18350 tube do mesh and fit the SP40 head. I’m sure this is not intentional from Sofirn but a quirk from the thread form allowances – that’s to say the female threads have a slack allowance that permits the crest part of the square to interact. As I had mentioned in an earlier post, the trap thread form is partially incorrect. It is too large in the groove (the width of thread acceptance).
Pictures better describe the fitting:
The left is a properly cut trap: equal groove area as the flange area. Sofirn’s machining on the right: groove is larger.
And as the square male thread fits into the female trapezoidal it is tighter.
Going into a rabbit hole on thread form. To make a thread on CNC you use a specific insert for the pitch and to allow for fitting allowances, the tool can be programmed with a lead-in (offset Z) to widen the groove on the second pass (typically with square threads). With trapezoidal threading, the depth of cut makes for the allowance. As there is minimum thickness consideration on the tube, the operator (or tool programmer) made the allowance for the square thread method.
And then there is the possibility of having an improper tool…
Edit Feb 29 ’22: fixed the picture links.
The difference is clear to see, thanks for the pics.
Received the correct 18350 short tube just a few days ago. Only 2 weeks and a few days after the email with the tracking number! Thank you Sofirn for the great service. The threads on the new short tube of course match the threads on the standard 18650 tube - so voila - we have the two-hued SC31 Pro short tube with mag tailcap from the SP40. Now I need another short tube and mag tailcap for the SP40.
Great…hassle to sift through but I’m glad they took care of you and now you have what you should have had at first. Wouldn’t it be great if all of the host manufacturers could just decide on a common set of threadforms for the various diameters.
Correllux, any idea why I get this when trying to post? Anyone? Now it’s working.