Frustrated with freeze offs on the left print head

WW4
Posts: 1
Joined: Wed Feb 26, 2020 11:56 pm

Frustrated with freeze offs on the left print head

Postby WW4 » Thu Feb 27, 2020 12:52 am

Hi I am very frustrated with my Pro2Plus. I have read what I can on these forums and others read books and consulted with friends that make great prints. I have had several projects freeze off the nozzle at roughly the same place, like 7 times. At first I was chasing clogs and nozzle size all sorts of other theories but when I came across "heat soak" it dawned on me (sometimes it takes a while) that there was something seriously wrong with the Pro2 design. What hit me was, the right nozzle never freezes, only the left one. What's the difference? The problem isn't real obvious until you disassemble the whole head and start to look at the cooling issues of the two head design.

First off some background. I have been printing with mostly PLA set around 210deg C. My parts are mostly thin wall housings for PCBs, nothing terribly hard to print. Prints that take under an hour usually squeak by. When I get the freeze off I have to completely disassemble the heads to get the filament out as it has locked up solid in the top section of the heat sink. It makes a perfect smooth swage shape of the inside of the nozzle.
So my understanding of what happens in heat soak is that that the whole head assembly gets hot enough to transfer heat to the filament as it travels inside the upper head. Now that the head assembly is warm it makes the filament soft and the first thing that happens is if the pinch gear is too tight it engraves ridges from the gear drive teeth which increases the effective diameter like knurling on a lathe. next it travels down getting hotter and as the pressure increases (axially) from driving the filament into the restrictive nozzle, the filament swells in diameter. Think of what happens to a balloon when you squeeze it, it gets fatter. now if there is any lull in the flow of one nozzle the plastic high up has swollen and frozen against the wall of the feed tube and it locks up solid.
OK why well if yo look closely at the raise head, there is a servo in back behind RIGHT the nozzle heat to sink. My theory then changed to "OMG" they have blocked off the airflow to the right heat sink. no wonder it's getting heat soak.
So I did what any of you guys would do I modeled the whole Raise 3D head in Solidworks and did a CFD analysis of the airflow. Sure enough the servo blocks the free airflow by a factor of 5 between the left and right heatsinks. So I set into a design that might better distribute the airflow evenly. You can always add more air with bigger fans but you can't really fix the dead end way over in the back corner. I also noticed in the CFD that the heat sinks are very inefficient and poorly designed. The gaps are too narrow between the fins which at low pressures like we have with a wimpy axial fan do not exchange air well.
I have now spent about 60 hours redesigning the servo mount and heat sinks. the CFD shows a significant (5x) flow which is EVEN across both heatsinks. The heat sinks have been redesigned to allow high flow at low pressure.
I am a lot better at design that CNC programming so it takes me days to get a program to run on my lathe or mill. but I am closer.
Pictures are attached of the progress I am not too sure how to post a link to the CFD video so if anyone knows how I will do that too.
Stay tuned.

AssyRaiseFullHead1.JPG
AssyRaiseFullHead3.JPG
AssyRaiseFullHead2.JPG
RaiseProgres1.jpg

mdana
Posts: 92
Joined: Mon Oct 07, 2019 1:36 am

Re: Frustrated with freeze offs on the left print head

Postby mdana » Mon Mar 02, 2020 10:57 pm

Nice job. The heat sinks on the previous generation were roughly double the size of the Pro2 printers, so I’m not sure how they thought this would work. I am in the process of converting to water cooled heat sinks (using the water cooling kit from E3D).
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Naser404
Posts: 89
Joined: Wed Jun 20, 2018 3:33 pm

Re: Frustrated with freeze offs on the left print head

Postby Naser404 » Wed Mar 04, 2020 3:33 pm

I replaced mine with E3D hotends, i had to modify them a little on the lathe but they work very well with the STD cooling too. I had to design another cooling duct though but most parts from the original raise is used.
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Naser404
Posts: 89
Joined: Wed Jun 20, 2018 3:33 pm

Re: Frustrated with freeze offs on the left print head

Postby Naser404 » Thu Mar 05, 2020 4:29 pm

WW4 wrote:OK why well if yo look closely at the raise head, there is a servo in back behind RIGHT the nozzle heat to sink. My theory then changed to "OMG" they have blocked off the airflow to the right heat sink. no wonder it's getting heat soak.
So I did what any of you guys would do I modeled the whole Raise 3D head in Solidworks and did a CFD analysis of the airflow. Sure enough the servo blocks the free airflow by a factor of 5 between the left and right heatsinks. So I set into a design that might better distribute the airflow evenly. You can always add more air with bigger fans but you can't really fix the dead end way over in the back corner. I also noticed in the CFD that the heat sinks are very inefficient and poorly designed. The gaps are too narrow between the fins which at low pressures like we have with a wimpy axial fan do not exchange air well.
I have now spent about 60 hours redesigning the servo mount and heat sinks. the CFD shows a significant (5x) flow which is EVEN across both heatsinks. The heat sinks have been redesigned to allow high flow at low pressure.
I am a lot better at design that CNC programming so it takes me days to get a program to run on my lathe or mill. but I am closer.
Pictures are attached of the progress I am not too sure how to post a link to the CFD video so if anyone knows how I will do that too.
Stay tuned.


I think the issue is more than just blocked air flow, i too reversed engineered the Raise head but if you open the heatsink on each nozzle you will realize two problems.
1- The heat sink is too small to rid of the heat.
2- The tolerances between the heatsinks and heat throat (not sure of the name, where the filament runs inside) is too big and therfore that small heatsink is not really capturing the heat well enough.

Of Course Air flow as mentioned always plays a big factor.


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