It’s the second time I’m tightening mine, and they probably need it more often than I’ve been doing it. It’s easy to see why with all the vibrationi during printing. Red Loctite may be overkill, as it’s hard to reverse, but maybe blue loctite would hold them good enough?
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Red is a more permanent loctite, I would use blue.
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Yeah. Do not use red. Blue is designed to be removable. Red is designed to be permanent.
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OK, so is anyone using blue Loctite on the screws of their H2D printhead?
I’m planning but haven’t done it yet. My concern is that maybe oneday there’s something bad happened and I might need to replace the heater assembly and get wrecked by the blue loctite: I’ve seen people posting actual screws breaking in two pieces… from the assembly, and that’s hellish experience.
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I would use the green “wicking” loctite it will hold and you won’t destroy the screws if you need to remove them.
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You don’t ruin your screws with red Loctite either — it’s just stronger and holds better against vibration.
I use red Loctite on every screw in my aircraft that might decide to “unscrew itself” mid-flight.
I take them all out every 100 hours and haven’t wrecked a single one because of Loctite — but yes, I have murdered a few with the wrong tool. 
Nothing gets your heart rate up quite like seeing a screw casually rolling across the cockpit floor. 
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Ugh the problem is that the screws that bambu used are… well, delicate.
There’re plenty of horror stories for both A1 and even some H2D owners in other communities that I joined… Thus I’m always quite worried about it.
Purple (222) is the correct locktight to use on small screws.
Red needs heat to release without damaging small screws. Usually if you heat the tip of the wrench insert it for a few seconds and reheat before trying to take out the screw.
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Will purple Loctite withstand whatever proximate heat there may be on the printhead?
Anyone here using purple Loctite with success?
I seem to vaguely recollect that on either my Qidi printer or my Creality printer (not sure which) the manufacturer used blue Loctite, but I’m not 100% sure I’m recollecting correctly. I haven’t encountered purple Loctite before, but I am very curious to learn more about it.
I have used red loctite to secure some bolts on a paint shaker (talk about vibration!), but it did require a blowtorch to unscrew them later.
Purple is a cross between red and blue, though in my experience with it on RC models(petrol, nitromethane and electric, but especially petrol), it’s more like blue with a slight “kick”. It doesn’t require, again in my experiences the heat that red requires. Red is a screw and bolt killer if you don’t know what you’re doing. Even blue can be in that case also. Green is the worst if you clean the screws with acetone! But anything that vibrates at very high frequencies like these, I would apply locktite.
Cleaning the screws or bolts “properly” can and will make any of them difficult and even with the hardest screws, they can be stripped and torn apart… Electronics like our printers, I would clean the screws in acetone (just let them sit for maybe 10 seconds, pull them, and let them dry well), and only apply the lock to the tip and up to 2 turns at most. And I would only use jell of whatever variant…
I have seen the blue on some of the bolts in the machines(printers) over the years, but it doesn’t seem anymore difficult to loosen than one of my non locked “kit” bolts… I also am extremely careful on any screw that’s 3mm or smaller, and only use “good quality” drivers. A bad driver is worse than a bag screw, and far more common…
The temp range for Purple is -65 to 150C
Seems like it would be worth a shot then. It can’t be any worse than the current situation, which is no Loctite of any kind whatsoever. May have to apply it with a tiny tip syringe (as close to hypodermic needle as possible?) just so as not to overdo it on such small screws. I may need to find a homeless encampment to get a free government issued needle or something. 
Unless the rules have changed, the last time I checked you need a prescription to buy a true hypodermic needle. But then again, maybe legal hobby needles will be good enough.
Or maybe I’m thinking about this all wrong. Perhaps just dipping the screw and then wiping off the excess Loctite would give a superior result? i.e. leaving enough Loctite on the threads, but without excess. I have no experience in applying loctite to such tiny screws, so maybe someone on this thread can advise who has done it before successfully?
In short:
How exactly?
When I assembled my Voron, I dipped the tips of the screws in blue 243 Loctite.
The glue only bonds under pressure. With a good fitting tool you should not have any issues to remove them again. In the worst case a bit of heat (as already mentioned above) can help.
I consider to use it on the tool head on the heating assembly.
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Reporting back:
I put the question to Grok, and it it suggested using a toothpick:
Apply the Loctite: Using the bottle’s thin nozzle or a toothpick for precision, apply a very small drop (just enough to coat the threads lightly) of purple Loctite directly to the male threads of the screw—focus on the engagement area where it will contact the hole.
Avoid applying to the hole itself or using too much, as excess can squeeze out, create mess, or inadvertently lock nearby components like the heater cartridge or thermistor.
Sounds reasonable. Somehow that answer was trained into Grok’s billions of parameters, so maybe that’s how it’s most commonly done? It’s consistent with @DameD 's incomplete answer.
I suppose I would focus on just the screws that I find to be loose, and leave as-is any that remain tight on their own. There are a lot of screws on the H2D printhead. I didn’t do an exact count, but I’d estimate more than half were loose to one degree or another, some much more than others. It can have a very noticeable effect on print quality, which is what clued me to re-check. If we only just re-tighten over and over, my hunch is that will eventualy lead to even more frequent loosening in the future. Right?
Speaking of which, what would be the ideal torque to tighten them to? I have a digital screwdriver that measures torque (doesn’t everybody?), so it’s not an academic question.
Not as expensive as you might think, right? I got mine for properly torquing screws in electrical panels, as required as per the newest NEC code. Perhaps we could do NASA level quality work if we had a proper torque recommendation for these smaller screws.
Reporting back: @Barryg41 suggests a torque of 1.15Nm,
and it got a thumbs up from @JonRaymond. Though the discussion wasn’t specifically about H2D, is it reasonable to suppose the same spec would apply?
For comparison, Grok recommends a lower torque:
For safety in 3D printer applications with soft materials like aluminum, aim for the lower end (e.g., 0.5-1 Nm) and consider using threadlocker like purple Loctite for vibration resistance.
Which raises a good point: in most cases, are we not threading directly into aluminum on the H2D hotend? i.e. we should account for the softer material? Or, if not, what material are we threading into? I haven’t taken an H2D hotend apart, and I didn’t pay enough attention when last I was tightening the screws to properly notice. The whole assembly is put together so tightly I’m not sure I even could notice just from looking at it in its fully assembled state. No obvious way to probe the screw holes with magnets either without possible confounding from nearby parts.
Which screws are the problem? Could you send any pictures? I have a H2D since 8 weeks. Would it be necessary to tightening my screws also?
You could wait until you see artifacts in your prints, but I would guess your H2D printhead probably already has some loose screws if you’ve been using it regularly for the past 8 weeks. Others may have a different opinion on that, and I would encourage them to post any contradictory opinions they may have so that we can all learn together.
In any case, it’s easy enough to test. Remove your hotends and then probe everywhere see a screw with an appropriate size hex key to see whether or not it is loose (i.e. by whether or not you can tighten it further). IIRC, only two hex sizes are needed to probe them all. I didn’t take note, but I think they were probably 2.0mm and 1.5mm drivers that fit all the screws.
It’s easy. You just watch the threads. Don’t “dunk” it, but turn it slowly. You do it a few times and it becomes second nature…
I will say, take a little bit of locktite and place it on a piece of plastic… Never from the bottle to the screw… That’s what makes a mess, and uneven coating it… Once it’s on the plastic, and you begin turning like you’re threading it in, it’ll get on there. You really need very little TBH…
One drop of loctite goes a long way…
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And what was your method for torquing them? By measurement, or simply until they felt subjectively “snug”, which, given the loctite, might be good enough I suppose.