water cooled extruder: what do you think?

Hello,
So it seems like when I fix one issue, another one pops up. I just recently wasted a day of work and a few ounces of plastic because the extruder jams after about 4 hours of use. I know what the problem is. It's a poorly designed extruder and the heat eventually works its way up to the cold end.

I noticed a few obvious issues: first, the threaded tube just sets into a drilled hole and held in with a set screw. There is very little contact surface area to transfer the heat from the tube into the aluminum block for the heat sink to 'carry away'. So the first thing I did was to apply some heat sink thermal compound to the threads of the shaft where it goes into the aluminum block, and then I put some compound between the block and the heatsink. This alone may have been enough, but I really don't want to take any more chances in wasted time and materials.

So, I made it water cooled. I wrapped a small piece of capillary tube around the top of the threaded tube, and pump cold water through it during the print.

I know most of you would just say to throw the junk extruder away and buy a new one. But there are a few reasons why I didn't. First, mainly, because I'm cheap. This mod cost me nothing. I already had everything I needed. Also, I did look at a few different hot ends, but they didn't look like they would fit the rest of my extruder. I didn't want to spend money, and wait days for a part that may or may not fit.

So, I'm 30min into a 7hr print now. Hopefully it'll make it with out any issues. I'll let you know how it goes. If it does not work, then I'll look more seriously into a better hotend and or extruder. But I will need help knowing what to get that will work, and fit my printer, and not break the bank.

Let me know if you have any opinions on this.

Thanks,
Scott

Hi Scott,
I'm thinking that you don't actually want heat transferred from the heater block to the heat break (threaded tube). Ideally, the filament would soften instantaneously as it goes out of the heat break and into the nozzle. Any heat going into the heat break is a bad thing, IMHO. So the thermal grease in the threads may be counter-productive. But perhaps there should be grease in the threads of the nozzle?

Frank

I understand all of that. That is the problem in the first place. The heat is going past the heatbreak. It's doing this because the heat sink and cooling fan are not efficient enough. I'm trying to make it so the heat that migrates up to the cold end gets dissipated quickly so that it doesn't get hot enough to soften the plastic in the cold end.

As it was, when the heat worked up the threaded rod, there wasn't enough surface contact area between the threads and the aluminum block that the heat sink is on. By adding the thermal compound, that gives the heat a path to the aluminum block, and to the heat sink, where the fan can blow it away. Without the compound, the heat just sits there in the threaded rod with no place to go. So It gets hotter, and hotter, until it softens the plastic (four hours later) and jams the extruder.

At the moment it's been printing longer than it ever was able to, with no problems.

Or think of it like this.

If you take a piece of metal and heat one end of it, the heat will move toward the other end. Even with a heat break. We need to remove that heat before it causes any problems. Hence the heat sink. For the heat sink to work, the heat needs to be able to flow to it. That's what the thermal compound does. It helps the heat flow to the heat sink. It does not pull the heat toward the cold end. It does not make the cold end hot.

But just in case this is not enough, the water should keep it cool by removing the heat as well.

Yes, the water will cool it, and that's a good idea.

But I still disagree about the thermal compound between the heater block and heat break.

You do NOT want an easy path for heat to travel from the heater block to the heat sink. The idea of the heat sink is to cool the heat break, NOT the heater block. You want as little heat to flow from the block to the heat break as possible, so you want to MINIMIZE heat transfer from the block to the heat break. To keep the heat break at the coolest temperature possible, you also want to maximize heat transfer from the heat break to the heat sink, so thermal grease in those threads is a good idea.

Is the heat creeping up through the heat break, or is the motor heating up and causing the problem? Maybe you need to adjust the motor current...

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

I understand our disagreement now. We actually don't disagree, I either didn't use the correct terminology, or you didn't understand my explanation. I'm not trying to transfer heat from the heater block to the heat sink. I was talking about the aluminum block that the heat sink is on. I am NOT putting it between the heater block and heat break. I'm working on the cold end. Trying to keep it cold.

Like I said, some heat will naturally go past the heat break (if it didn't, we wouldn't even need the heat sink or fan). In order to quickly get rid of that heat, it has to be able to easily get to the heat sink. That's what the compound does.

However, it failed. The print job should have been 10 hours (I think I said 7 before), and it failed at 7 1/2 hours. Which is 4 hours longer than it has ever lasted. So I'm on the right track. But I think it's time to admit defeat and buy a good hot end. It's weird though, when it failed the cold end still felt cold, so I'm not really sure why it stopped extruding. It was easy to pull the filliment out and reinsert it, and start printing again. It didn't seem like a jam this time.

So I need to know what will work for my extruder. I'm looking at the E3d v6 hot end. But I'm not sure exactly the best way to attach it to my extruder.
Any help?

Thanks

Quote
the_digital_dentist
Is the heat creeping up through the heat break, or is the motor heating up and causing the problem? Maybe you need to adjust the motor current...

That is a good thought, and, I'm not sure. I didn't notice if the motor was real hot or not. The aluminum block that connects to the motor that the threaded rod/heat break attaches too didn't feel warm. And I actually tuned the extruder motor down a few days ago. It was making a growling noise that was actually making visible wave patterns in the prints. So I tuned it down until it was quit. So I don't think that's the problem, but I'll check it out next print.

I have found that sometimes cold is too cold. a project I am working on ( which is water cooled) would jam at the top of my barrel. The trasistion from hot to cold was so sharp that on retraction the filament would solidify almost instantly, and cause a jam.

back to topic:
I would check the shaft on the extruder to see if it gets hot enough to soften the filament and cause it to slip.

Quote
cat.farmer
I have found that sometimes cold is too cold. a project I am working on ( which is water cooled) would jam at the top of my barrel. The trasistion from hot to cold was so sharp that on retraction the filament would solidify almost instantly, and cause a jam.

If that were the case, would the problem show up right away or several hours into the print?


back to topic:
I would check the shaft on the extruder to see if it gets hot enough to soften the filament and cause it to slip.

That could be a problem. Not sure of the best way to actually check that though. I am considering installing a geared extruder with an E3D hot end. That would probably cure all my problems.

Quote
koenejet

Quote
cat.farmer
I have found that sometimes cold is too cold. a project I am working on ( which is water cooled) would jam at the top of my barrel. The trasistion from hot to cold was so sharp that on retraction the filament would solidify almost instantly, and cause a jam.

If that were the case, would the problem show up right away or several hours into the print?


back to topic:
I would check the shaft on the extruder to see if it gets hot enough to soften the filament and cause it to slip.

That could be a problem. Not sure of the best way to actually check that though. I am considering installing a geared extruder with an E3D hot end. That would probably cure all my problems.

Sorry, I didn't quote that the right way. One of my questions ended up in the body of your comment on the last quote.

So a couple of you suggested it could be heat from the extruder motor. It just finished a 2 1/2 hr print and the extruder motor measured 30*c with an infrared temp sensor. I don't think that's hot enough to cause problems, is it?

Just a follow up in case any one is wondering.

A few posts back I said a print failed. Well I didn't really have much heat sink compound between the copper tube and the cold end, so I applied quite a bit more to make sure the water cooling would be as efficient as possible. Yesterday the printer completed a 14 1/2 hour print without fail. That's the longest it has printed so far and could probably have kept on going.

I'm mainly posting this in case anybody else is having the same problems. This may not be the best fix for everyone, but for me, it works great.

Thanks,
Scott