How do you seal your heat block? I'm having a consistent issue with sealing the heat block on my printers. Last night my printer decided to puke a little blob of melted crap onto my print (I managed to remove it before it ruined the print, but only because I happened to be watching at the right time.) I've started looking into how to seal these, and I've run into a few roadblocks. So, I figured that I'd ask how people do things. To date, the only time that I haven't had a problem was my very first printer, which never leaked. I've no idea how that heat block was sealed, but I couldn't get the nozzle or throat out of the heat block either. Every other time I've had problems with molten plastic seeping from the heat block on either the throat side, nozzle side, or both. Given that the thread in the heat block is a standard metric thread, and not a pipe thread, these are typically not intended to actually seal, Add in the fact that most of these nozzles are brass, and the heat blocks are aluminum (and many of the heat breaks or throats are stainless steel) there is also a problem of dissimilar metals and thermal expansion to deal with. I had assumed that the throat (or heat break) and nozzle were just jammed together very tightly inside the heat block to seal the join, but that doesn't seem to work, or else it takes more torque than I've wanted to apply. I looked at "high temperature thread sealant" which I have a lot of. I have some that is meant to seal threads for automotive use, like engine bolts that go through to the cooling or oiling passages, and still allow the bolts to be taken out later. These are rated good to 204 deg C, which isn't quite high enough. The nice thing is that they do deal with dissimilar metals (Bolts typically steel, cylinder heads typically aluminum) so I know that it can be done. In the automotive area, I have some stuff that's intended to seal exhaust systems (Good to 2000 deg F/1100 deg C) but is never intended to come apart again. I'm actually really tempted to use this and just assume that if the time comes I'll just be replacing the whole assembly of nozzle, heat block and throat. I'd rather use something like a thread sealant which is intended to let stuff come apart again afterwards, but the peace of mind that I'm not going to get molten plastic seeping out of joints that it shouldn't would be worth a lot to me. Anyway, am I just missing a simple trick somewhere? https://reprap.org/forum/read.php?4,834732,834732#msg-834732 Fri, 17 Apr 2026 08:18:51 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?4,834732,837852#msg-837852 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837852#msg-837852
I still need a new heat block anyway, since I'm still not using the PT1000 sensors that I bought, but there's a mail strike on now, so I haven't got a new block yet. I want to see if this method is good first anyway.

And yeah... I kind of thought that teflon tape wouldn't be a good idea if the idea is to want to be able to have the higher hot-end temperatures.

I was considering a paper gasket. These get used in automotive applications for service up to about 300 deg C, even though the combustion temperature for paper is 233°C (Or as made famous by Ray Bradbury, 451 degrees Fahrenheit.) The paper won't burn if it's not exposed to enough oxygen, but I've always considered it to be risky.

I don't have any aluminum or copper crush washers small enough to use in a hot-end like this. Most of these that I have are for larger fittings, 12mm ID or larger, or else I'd have used one. I have some head gasket sealant that is, so far as I can tell copper dust with just enough of some volatile petroleum product to make it stick together. I might use this on the nozzle, since it should also have excellent thermal conduction properties. I'm not sure what the thermal conduction of the Permatex stuff is, since it also has silicone, but it's rated to 371°C, so it's more than good enough for the heat break, but I'm not sure that I want it between the nozzle threads and the heat block. I'm okay with it between the nozzle and the heat break though, so that's how I arranged it. It still seems to work well for running the plastic through, doesn't seem to have hurt extrusions at all.]]> SupraGuy Reprappers Tue, 06 Nov 2018 10:48:25 -0500 https://reprap.org/forum/read.php?4,834732,837808#msg-837808 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837808#msg-837808
Quote
Trakyan
Not much point in using an all metal heatbreak if you'll wrap the threads with plumbers tape (teflon).

Nope. That one still used a PTFE core. Totally a Frankenstein's monster hot end in that printer. Built with "sorta fits" and "what I have in the junkbox" parts.
I have a full replacement for it when I rebuild the entire thing. At the moment it works for creating large test prototype parts with a "fire hose" nozzle.

DLC]]> dlc60 Reprappers Mon, 05 Nov 2018 17:21:39 -0500 https://reprap.org/forum/read.php?4,834732,837725#msg-837725 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837725#msg-837725 Trakyan Reprappers Sun, 04 Nov 2018 18:10:19 -0500 https://reprap.org/forum/read.php?4,834732,837572#msg-837572 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837572#msg-837572 I've successfully assembled (I think) 10 hot ends. One thing that helps perhaps is that I have a zero tolerance for problems. If I have any trouble whatsoever I replace the heat break. If possible, I replace it with an "all metal" one. I have one that ended up with an interesting configuration of parts that were not quite factory stock.

I did have one massive heater block that always leaked out the top (next to the heat sink). A couple of wraps around the thread with plumbers tape solved that problem.

DLC]]> dlc60 Reprappers Fri, 02 Nov 2018 14:48:50 -0400 https://reprap.org/forum/read.php?4,834732,837554#msg-837554 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837554#msg-837554
I'll be very sparing with the sealant, and I have some of those nozzle cleaners. I'll probably assemble it with the cleaner in place, and just cold-torque the nozzle into place with a light layer of sealant on the mating surface, and since it's copper based, maybe cover one thread or so on the nozzle and heat break. the last thing that I want is extra sealant going into the melting chamber of the nozzle or obstructing the filament in the heat break.]]> SupraGuy Reprappers Fri, 02 Nov 2018 10:36:16 -0400 https://reprap.org/forum/read.php?4,834732,837510#msg-837510 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837510#msg-837510
Heatbreaks should not be threaded but conical , flared like high pressure hydraulic coupling. It is the way I make my own.]]> MKSA Reprappers Thu, 01 Nov 2018 18:38:05 -0400 https://reprap.org/forum/read.php?4,834732,837499#msg-837499 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837499#msg-837499
I do have a tube of this in the garage: [www.permatex.com]

I'd almost forgotten that it was there, I bought it to seal an oil cooler line, but ended up replacing the oil cooler with something that used BSPT threads instead. This stuff is supposed to be good to 371°C so it should certainly stand up to 3D printing temperatures.]]> SupraGuy Reprappers Thu, 01 Nov 2018 15:38:35 -0400 https://reprap.org/forum/read.php?4,834732,837496#msg-837496 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837496#msg-837496 Fact is, most hobbyists who recently started "designing" 3D printers have no clue about mechanic, or just theoretical but not practical !
Thingiverse gives a pretty good timeline how things went down the drain overs the years.
Chinese copiers try hard to make bad designs worse and the few good ones, really bad. Their success rate in doing so is amazing. :)]]> MKSA Reprappers Thu, 01 Nov 2018 13:44:03 -0400 https://reprap.org/forum/read.php?4,834732,837494#msg-837494 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837494#msg-837494
I believe that the fact that it was good for a while, and is definitely not now must have to do with heat cycles and dissimilar metals. (Stainless steel throat, brass nozzle, aluminum block) Something must be deforming under heat, and not coming back to the same position the next time.

@MKSA: Yep. That's how I'm going to do it.

As it happens, I was about to be changing the heat block anyway, since I now have some PT1000 sensors, and I need a different heat block that can fit the cartridges.

Thanks for being patient with me. I do a LOT of DIY type projects, and I'm generally (If I do say so myself) pretty good at it.

To me though this method of tightening the nozzle and heat break together to form a seal is something that I would just never see in other applications.

In anything automotive related, there would be a flange and gasket system, particularly if there needed to be a temperature range tolerance. that would mean a flange on the nozzle and another on the heat break, and both would be gasketed against the surface of the heat block. Alternately, the threads could be tapered to force a sealed fit under torque, like BSPT or NPT threading. It seems to me that with the need for good thermal contact would make this a superior solution.

I'll start going through my assorted collection of crush washers to see if I can find one that will work inside the 6mm thread of the heat block. I have some aluminum and copper ones, meant for a fuel system, and some fibre ones meant for oil systems. Either one should be fine to for any temperatures that I'm ever going to print at. I also have some sealant meant for metal head gaskets which might just do the trick, which also doubles as an anti-sieze compound.]]> SupraGuy Reprappers Thu, 01 Nov 2018 13:05:31 -0400 https://reprap.org/forum/read.php?4,834732,837457#msg-837457 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837457#msg-837457
Quote
SupraGuy
Spoke too soon.

It's definitely leaking between the heat block and nozzle threads, and is gradually getting worse. The top pf the heat block is staying clean, thanks for small miracles, but I'm getting an occasional booger of melted plastic dripping onto my printed parts. I cleaned it all up really well, and watched for a while. After a few minutes at 240°C there is a small bubble of melted plastic that appears on the side of the nozzle towards the heater.

This was a new heat block, new throat and new nozzle. I only re-used the actual heater unit from before. the screw for the heater was tightened until the heater was secure to a little bit of a pull on the wires. It was then heated to printing temperature, and then the nozzle was torqued tight. I did not heat it beyond printing temperature this time. The nozzle appeared to be flush against the bottom of the heat block when it was done.

Screw this. I'm putting a crush washer in next time.

I told you :)
An Al washer INSIDE of course, crushed between the nozzle top and the heartbreak bottom, easy to make if you can't buy it. First thing I made years back on a crappy leaking Geetech hot end.
AND the nozzle must be AWAY from the heat block. You should expose the non threaded nozzle portion.]]> MKSA Reprappers Thu, 01 Nov 2018 00:29:00 -0400 https://reprap.org/forum/read.php?4,834732,837456#msg-837456 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837456#msg-837456 the_digital_dentist Reprappers Wed, 31 Oct 2018 22:10:58 -0400 https://reprap.org/forum/read.php?4,834732,837455#msg-837455 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837455#msg-837455
So here's the procedure:

  1. Get the heater block up to temperature (otherwise pieces of solid plastic may get between the nozzle and heat break).
  2. Loosely screw the nozzle all the way in, then back it off by a quarter turn or so. (Use pliers or a spanner to hold the heater block to avoid burning your fingers, melting plastic items, scorching your desktop, etc as you fiddle with the hot heater block).
  3. Screw the heat break all the way into the heatsink.
  4. Use the heatsink to screw the heat break all the way into the heater block (finger tight).
  5. Tighten the nozzle against the heater block, with spanners. This will seat the nozzle hard against the end of the heat break, without putting any stress on the heat break, which is not strong.

Probably some thermal conductive grease, as used on computer CPU coolers and so on, would be good on the nozzle threads and the heatsink thread.

Wrapping some insulation around the heater block will make your nozzle temperature more stable (and save a little money).]]> frankvdh Reprappers Wed, 31 Oct 2018 21:39:31 -0400 https://reprap.org/forum/read.php?4,834732,837454#msg-837454 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837454#msg-837454 the_digital_dentist Reprappers Wed, 31 Oct 2018 19:43:20 -0400 https://reprap.org/forum/read.php?4,834732,837450#msg-837450 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,837450#msg-837450
It's definitely leaking between the heat block and nozzle threads, and is gradually getting worse. The top pf the heat block is staying clean, thanks for small miracles, but I'm getting an occasional booger of melted plastic dripping onto my printed parts. I cleaned it all up really well, and watched for a while. After a few minutes at 240°C there is a small bubble of melted plastic that appears on the side of the nozzle towards the heater.

This was a new heat block, new throat and new nozzle. I only re-used the actual heater unit from before. the screw for the heater was tightened until the heater was secure to a little bit of a pull on the wires. It was then heated to printing temperature, and then the nozzle was torqued tight. I did not heat it beyond printing temperature this time. The nozzle appeared to be flush against the bottom of the heat block when it was done.

Screw this. I'm putting a crush washer in next time.]]> SupraGuy Reprappers Wed, 31 Oct 2018 17:36:50 -0400 https://reprap.org/forum/read.php?4,834732,835829#msg-835829 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835829#msg-835829
Overall, I think that I've got it. the build-up on the nozzle is annoying, but I think that's a matter of dialing in the temperature and print speed. I might have to tune extrusion, too. I think that it's right, so I'll see about temperature and speed first.

I re-did the hot end of my other printer as well, but have not yet had a chance to test it.]]> SupraGuy Reprappers Tue, 09 Oct 2018 10:57:31 -0400 https://reprap.org/forum/read.php?4,834732,835782#msg-835782 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835782#msg-835782 This has worked every time, with every E3D and Cheap-shlock hot end I own. I have several different flavors.

I have read a couple of folks say tighten the nozzle to the heater block, then back it out a couple of turns. There aren't that many threads on most of my nozzles to do that, I back the nozzle out to leave me about a 1mm gap, then snug in the heat break, then turn on the heater and wait to 245 C, then 5 minutes. Tighten.

I have had a few hot ends that would leak after this. I have learned _NEVER_ to fuss with the hot end at this point, I get another heat break and try again. Almost every time, the second heat break snugs well and does not leak. On one and only one occasion, I resorted to using teflon plumber's tape on the heat break going into the heater block to stop a leak there. I buy "all metal" heat breaks for all of my hot ends, I do not use PTFE-centered heat breaks in anything-you can find all kinds of cheap all-metal heat breaks out there. The majority of them even work :). I have fewer serious issues with clogging when I eliminate the PTFE liner.

My only "drool" problems now come from ooze out of the nozzle, I am working on wipers for a few of my printers to help with that.

Maybe I am getting lucky, but so far my success rate with the above is 100%.

DLC]]> dlc60 Reprappers Mon, 08 Oct 2018 18:18:42 -0400 https://reprap.org/forum/read.php?4,834732,835767#msg-835767 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835767#msg-835767
Done, hot tightened, and seems not to leak. I just ran a test vase print, about an hour, but I don't see any leaking. Other issues, temperatures seem different than the other one, but no leaking.]]> SupraGuy Reprappers Mon, 08 Oct 2018 12:42:23 -0400 https://reprap.org/forum/read.php?4,834732,835695#msg-835695 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835695#msg-835695 the_digital_dentist Reprappers Sun, 07 Oct 2018 07:36:37 -0400 https://reprap.org/forum/read.php?4,834732,835685#msg-835685 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835685#msg-835685 MKSA Reprappers Sun, 07 Oct 2018 03:11:34 -0400 https://reprap.org/forum/read.php?4,834732,835608#msg-835608 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835608#msg-835608
Anti-seize compound will help prevent the threads in the aluminum from getting galled by the steel heatbreak and the brass nozzle. By keeping the set screw threads from doing the same, a tool will turn the screw instead of chewing up its head.

[www.fastenal.com]]]> the_digital_dentist Reprappers Fri, 05 Oct 2018 14:05:08 -0400 https://reprap.org/forum/read.php?4,834732,835592#msg-835592 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835592#msg-835592
I discovered the problem. When it cooled, the throat deformed the threads in the aluminum heat block instead of sealing nicely to the nozzle. I think that the 285 deg C temperature specified in the E3D write-up is allowing for some temperature loss when the cold wrench is put on things. I'm quite confident that I did not over-torque.

I put together a new heat-block, nozzle and throat, but have not hot-tightened it.

I'd like to test it, but I'm not sure what I can test it with. De-ionised water will at least tell me how it is when cold, but not hot, but if I do that before putting any plastic through it, that may be good enough.]]> SupraGuy Reprappers Fri, 05 Oct 2018 10:34:09 -0400 https://reprap.org/forum/read.php?4,834732,835554#msg-835554 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835554#msg-835554 the_digital_dentist Reprappers Fri, 05 Oct 2018 00:29:13 -0400 https://reprap.org/forum/read.php?4,834732,835553#msg-835553 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835553#msg-835553
Quote
the_digital_dentist
The teflon in most (some?) doesn't extend down to the heater block- it stays up in the heatsink, so it never sees the high temperature.

Except in all metall hotends, there is always? a short piece of 3OD x 2ID mm PTFE tube in the bottom of the heatbrake. Right where the heat is.
But I can only refer to clones.]]> o_lampe Reprappers Fri, 05 Oct 2018 00:25:15 -0400 https://reprap.org/forum/read.php?4,834732,835541#msg-835541 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835541#msg-835541
I'm assuming that something here is out of square, it seems the most likely explanation. I ordered a whole new hot-end, and my Amazon app said that it was delivered about a half hour ago, so it should be in my mailbox when I get home. Also in the package is a bag of thermistors, a selection of nozzles, and some 24V fans plus for good measure a couple of RPi cameras. just me being the way that I am, I may make one more attempt to seal this thing up for once and for all. I'm not sure that I can check the end for square with what I've got, not accurately enough.

If I use a crush washer, I HAVE copper ones. I don't have aluminum, and I'm unlikely to buy anything for this (Might as well just use the new one.) Yeah, it throws one more metal into the multi-metal mess that is the aluminum heat block, stainless steel heat break and brass nozzle, but I have more than I hope to ever need. At this point though I'm just as likely to throw thread sealant (Which is also supposed to act as anti-sieze) at the problem. For these parts, I strongly suspect that once they leak, they're never going to seal properly. The same problem happens in engine blocks with some brass and aluminum fittings. If you ever let the engine heat cycle without them properly seated and sealed, they're never going to seal right, unless you completely re-machine the seating surfaces. (One more use for that lapping block that I have.)

I will take care with the new hot end to seat it right the first time, hot-tightening it, this time using the controller the way that the E3D tutorial says. If it leaks, I'll use a crush washer, but not before swearing at it for as long as it takes me to disassemble and clean all of the parts.]]> SupraGuy Reprappers Thu, 04 Oct 2018 18:18:16 -0400 https://reprap.org/forum/read.php?4,834732,835512#msg-835512 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835512#msg-835512 the_digital_dentist Reprappers Thu, 04 Oct 2018 12:20:27 -0400 https://reprap.org/forum/read.php?4,834732,835508#msg-835508 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835508#msg-835508 MKSA Reprappers Thu, 04 Oct 2018 11:28:47 -0400 https://reprap.org/forum/read.php?4,834732,835506#msg-835506 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835506#msg-835506 the_digital_dentist Reprappers Thu, 04 Oct 2018 11:21:56 -0400 https://reprap.org/forum/read.php?4,834732,835502#msg-835502 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835502#msg-835502
Quote
https://e3d-online.dozuki.com/Guide/V6+Assembly/6?lang=en
Step 26 Hot-Tightening
  • Hot-tightening is the last mechanical step before your V6 is ready to go! Hot-tightening is essential to sealing the nozzle and heatbreak together to ensure that molten plastic cannot leak out of the hotend in use.
  • Using your printer's control software (or LCD screen), set the hotend temperature to 285°C. Allow the hotend to reach 285°C and wait one minute to allow all components to equalise in temperature.
  • Gently tighten the nozzle whilst holding the heater block still with a spanner and using a smaller 7mm spanner to tighten the nozzle. This will tighten the nozzle against the Heatbreak and ensure that your hotend does not leak.
  • You want to aim for 3Nm of torque on the hot nozzle—this is about as much pressure as you can apply with one finger on a small spanner.

So it's not like I'm pulling stuff out of my rear. These are the instructions for the genuine article, and while the one that I have is a clone, the clone seems similar enough in form that I'd have thought that the same assembly instructions would work, or at least I figured that using the oven to hit the same temperatures should if anything produce more consistent results, since I don't have the heat block and nozzle in contact with a cold wrench. I suppose that it's possible that they are taking into account the heat sink properties of the wrenches, though if that's the case, there's a time element that they should say to aim for, too.

I have heard of silicone gaskets inside of heat blocks. I probably have some small copper crush washers that I use to seal oil pressure fittings on my engine block, not sure if I have them in the correct size, but that's another solution that I'd be willing to try. Most of those fittings are BSPT in order to seal tightly, but there are some that use a standard metric thread with the soft copper crush washers to form a seal. Those are typically between the bolt head and surface, and not inside the thread itself. A couple of places use a Viton o-ring which goes inside the threaded opening.

From an engineering standpoint, the idea of hot tightening the nozzle and heatbreak seems like a "good enough" solution. It's not ideal, there's a reason why things that need to REALLY seal use tapered pipe threads or gaskets and thread sealant, but all of those solutions cost a little extra money.

Hmmm. A Viton-90 O-ring is rated for up to 230 deg C, so maybe not quite good enough. I might look further into gasket materials good to ~300 deg C.

Should I need this? Almost certainly not. It probably doesn't take long before you get above the price range that perfectly working solutions cost, but something like the exhaust sealer is cheap to me, because I already have lots to spare in the garage. I may even have serviceable crush washer (Which is probably the ideal solution) or 20 already in the garage, too. Then I can probably just borrow torque specs from the car shop manual and not have to worry about it. It'll probably be easier to take apart again later, too.]]> SupraGuy Reprappers Thu, 04 Oct 2018 10:57:40 -0400 https://reprap.org/forum/read.php?4,834732,835484#msg-835484 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835484#msg-835484 the_digital_dentist Reprappers Thu, 04 Oct 2018 06:59:46 -0400 https://reprap.org/forum/read.php?4,834732,835465#msg-835465 Re: How do you seal your heat block? https://reprap.org/forum/read.php?4,834732,835465#msg-835465 I always tighten the hotend when cold. The only one leaking was the cyclops-clone, because nozzle and heatbrakes don't meet.]]> o_lampe Reprappers Thu, 04 Oct 2018 01:02:01 -0400