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?

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MBot3D Printer
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Leadscrew self-built printer (in progress)
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The ends of the heat break and the nozzle are usually designed and machined to fit together tightly to seal. The assembly technique is usually to screw both into the heater block until they touch, then, heat the whole thing up and do final tightening while it's hot. You can't usually twist the heatbreak because it will break, so you hold the heater block with one wrench and the nozzle with another to tighten them. Be careful not to make it too tight because the steel heatbreak and the brass nozzle will chew up the threads in the softer aluminum heater block. I always put anti-seize compound on everything that mounts in/on the heater block, including the heatbreak, nozzle, heater cartridge, thermistor, and lock screws. The anti-seize compound will smoke and stink a little the first time you heat up the hot-end, but that stops quickly. It guarantees that you'll be able to get everything apart when and if the time comes.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

For reference, my V6 hotend is a clone, but I did follow the instructions here: [e3d-online.dozuki.com]

Which does say to heat things up for tightening. I'm usually pretty careful about torque values, particularly when dealing with aluminum, and used a torque wrench to apply 26 in-lbs torque to the nozzle with the heat block in a vice with silicone baking sheet strips in the jaws. (The termperature drops fairly very quickly as soon as the room temperature socket fits over the nozzle, but it only took a few seconds to click in the torque.)

I'm also quite accustomed to the smell of heated anti-seize compound Smells like a freshly tweaked turbocharger to me. I have a few tubes of that in the garage, too.

So I guess what this comes down to is "That's what you get when you use a clone hot-end."

I suppose that I can try better parts, or else I can just accept that these ones suck, and use the exhaust sealant, knowing that they're never coming apart again. (Or both, order the better parts, and cement this together for now.)

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MBot3D Printer
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Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Tip for the day.

Once the heat block is leaking, just accept that it leaks.

So I pulled the whole thing out, took it apart, cleaned out the melted gunk. from the parts. Took out the metal throat, heat block and nozzle and put them in a 450 deg (230 deg C) oven and gave them a good brushing off to have them as clean as possible. Put them back in the oven at 550 deg (285 deg C) Also, the wrench that I was holding the heat block with and my 7mm socket was heated in the oven at the same time. Assembled everything at that temperature (It isn't easy to thread the nozzle in with oven mitts, in case anyone wanted to know.) Torqued the nozzle in.

The result is that it leaks worse now. I have to clean melted plastic leaking from around the nozzle threads about every 2 minutes while printing. Sooner if there are a lot of retracts during the print.

I have more more nozzles and heat blocks, but I don't have extra throat parts. I'll be getting a new set of 5 tomorrow or Friday.

Okay, so I know that the E3D instructions say to do the hot tightening by setting the temperature to 285C with the controller, and I guess they must use that temperature knowing that putting a cold wrench on the heat block will dissipate a lot of heat fairly quickly. I still thought that my method would yield more predictable results, as everything is heated evenly. The throat was screwed in about a half turn further than it was the first time, and the nozzle did seem to seat well in the heat block, but now it pretty much dribbles.

If I take this one apart again, I'll use automotive high temperature thread sealant. It's only really rated for 205 deg C, but that's supposed to be the temperature at which you are able to take it apart again afterwards. If I take this out again, I think it's safe to assume that I'm probably not going to do it ever again after that As is, I can't leave the printer running my itself, now, since I have to catch the melted stuff ont he side of the nozzle every few minutes.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

The ends of the heat break and the nozzle have to butt up against each other to seal. If either of the metal parts of the joint are damaged, it can't seal. Inspect the end of the heatbreak. If it's in good condition, replace the nozzle and it should seal fine. If the heatbreak metal surface is damaged, either polish it or replace the heatbreak. You should not have to add anything to get it to seal.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I suppose that I can try again.

I have a lapping block that I use for tool sharpening. It will give a smooth surface that should be better than anything coming out of a machine shop. (Single-digit RA -- roughness average -- for those of you who know how that works.)

I did verify that there was no visible damage to the nozzle or heat break seating edges, and that they did contact. I actually wonder if I somehow cracked something. I'll take it apart again to see what I can do, and replace the nozzle with a new one. I'll just use a new heat block too, since I have several brand new ones, and cleaning it is a pain. I do have a new hot end ordered from Amazon, should be here before the weekend. I'd like to get this resolved before then if possible.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

The nozzles shelf sits tight against the block, I've had leaks in the beginning but it was near the heatbreak, and out of the grubscrew holes, personally for the v6 i'm looking for a longer throat with heatbreak, so I can add a nut ontop of heatblock or above heatbreak(like i have on the v5)...so about 6mm longer then normal ones.

The nozzle should be screwed in first, all the way in, then backed out a turn or two. Then screw in the heat break until it stops against the nozzle. If you have the nozzle screwed all the way into the heater block, when you try to tighten it against the heatbreak, you'll be tightening it against the heater block, not the heat break, leaving a gap between the two, and it will leak.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Yep. I get that.

I had the throat and the nozzle screwed in together finger tight, then I backed out the nozzle, and screwed in the throat another turn, then tightened the nozzle. As stated earlier, I followed the instructions on the E3D wiki..

I wouldn't be surprised at this point to find that my clone heatbreak isn't flat/square on the end. I suppose that's the next test to see how it looks if I screw it right through to the other end, to see if the face of it it actually square to the threads.

I will assume that it's possible to seal without thread sealant, at least good enough for the viscosity of molten plastic.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

I wonder how a PTFE-liner inside the heatbrake will survive the 285°C treatment?
I always tighten the hotend when cold. The only one leaking was the cyclops-clone, because nozzle and heatbrakes don't meet.

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.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

As TDD said, the PTFE tube doesn't go into the heatbreak, and I'm taking that temperature straight from E3D's wiki, which I linked above.

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.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Thousands of people use clones and genuine E3D hot-ends every day and don't have leaking problems. If I were you, I'd replace the nozzle and heatbreak, and if necessary, the heater block and be done with it.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

To tighten when hot is indeed standard procedure. Leaks are mainly due to bearing surface poor surface finish or not being square. If needed, use Al washer instead of copper. No need for any Oring or anti-seize compound.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

I use anti-seize compound for everything that attaches into the heater block. It doesn't seal anything but ensures that it is easy to take the thing apart when necessary, and sooner or later, it will be necessary. When you consider how fragile the heatbreak is, anti-seize is a pretty good idea.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Anti-sieze is indeed a good idea, and I have lots.

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.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

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.

That's why I said "some", and it's an excellent reason not to buy that sort of worthless junk.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

So I have most if it taken apart. I can't get the heater cartridge out because the screw that pinches it has the head stripped out, I'll be drilling that out today, since I want to re-use the heater.

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.

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MBot3D Printer
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Leadscrew self-built printer (in progress)
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Wrenches are steel that doesn't conduct a lot of heat, so the effect on the temperature is relatively small in the few seconds it takes to tighten the nozzle.

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]

Edited 2 time(s). Last edit at 10/05/2018 02:14PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Again, an Al washer will solve this. Easy to make without special tools, just a sheet about 1mm thick, a drill, a punch, scissors, file. Copper is not soft enough.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Again, thousands of people use extruders every day without adding anything to seal the hot-end. Some problems are best solved with tools, others with a mouse. Spend the $10 or $15 and get a new heat break, nozzle, and heater block and be done with it. click, click...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Well, I had a few setbacks this weekend, so didn't get to the new hotend until late last night. I'd already ordered it, but the one that arrived came with a 12V heater, so I needed to get my 24V heater out if the old block.

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.

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MBot3D Printer
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Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Most of my hot ends have leaked initially if I didn't do a good job with the "heat tight" step. I got better with it over time. These parts are not all that robust, so I never used a spanner/wrench with a long handle. I also never went to 280C, even on my E3Dv6 heads. I went to 245 C, let it sit for 5 minutes or so, then tightened the system down with a pair of slip-lock pliers and a "thumb wrench" socket of the appropriate size. I could tighten the nozzle well without danger of breaking or galling anything.
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

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Kits: Folgertech Kossel 2020 upgraded E3Dv6, Anet A8 upgraded E3Dv6, Tevo Tarantula enhanced parts and dual-head, TronXY X5SA Pro(E3DHemera).
Scratch: Large bed Cartesian, exchangeable heads, Linear slide Delta, Maker-Beam XL Micro Delta, 220x220CoreXY.

Well, I ran a 4 hour print last night. I was getting some build-up on the nozzle, but I don't think that it was leaking. For once, the top of the heat block stayed clean, which is a huge improvement.

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.

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MBot3D Printer
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Leadscrew self-built printer (in progress)
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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.

Edited 1 time(s). Last edit at 10/31/2018 05:38PM by SupraGuy.

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MBot3D Printer
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Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

The nozzle should not be flush against the heater block. That is the problem. The nozzle should be off the heater lock when it's tight. Turn the heat break in another turn or two, then tighten the nozzle against it. You want to tighten the nozzle against the heatbreak, not the block.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Right. You want the nozzle as far into the heater block as possible, to get maximum thermal transfer to the nozzle. You want the heat break hard against the nozzle, to prevent leakage. Within those parameters, you want as little of the heat break inside the heater block as possible, to minimise thermal transfer.

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).

I give up...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

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.

Edited 1 time(s). Last edit at 11/01/2018 12:41AM by MKSA.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)