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J-head Cooling solution

Posted by DesignSmurf 
J-head Cooling solution
March 28, 2013 05:24AM
Hi .

While I was trying to fix some printing issues I found out that my printing temp was much too low to print proper in my new gray ABS (3mm filament, 0.35 nozzle) So upped the temp to 265 while printing and 260 to start with. It now smurfs nice but now I do get the top of the PEEK to overheat.

(following is a rough copy of my post in another topic from 3ddude about rapidbot owners)

After reading some issues with fellow rapidbot user from makemendel, and inspired by a possible solution by Hendo420, I set to design my first upgrade for this printer. A low weight J-head cooling mount and pressure chamber for a 40mm fan.

And her it is! It's a bracket that fits the top of J-head and slides 2mm over the top of the PEEK.
It uses a 40mm fan with 3mm mounting holes. (I used the same 3 mm stuff that came with the printer.)
I connected the fan to the Heater lines. (don't know if that is smart in the long run, but is seems to work nice for now)
When the heat is on the fan runs and blows air only past the top half of the PEEK tube.

The STL has a closed bottom surface you have to cut away (heated printbed not hot enough with this rapidbot) it prevents warping on a 60C bed. I also use a skirt with a minimum of 20 tracks. I printed with 0.1 layer thickness.

here some pics;

The air is pushed trough a small gap between the fanmount air chamber and the PEEK.
There is a small hole on the top for excess air to escape so the fan would run without to much
front pressure. it also give some bending space for bigger or smaller PEEK tubes.

I looked at a using a bigger fan, but it proved to big to fit nicely and had way to much air displacement for
cooling only the PEEK.

You can see the print was not very smooth. it looked better after some cleanup.
I disabled the retract filament option in Slic3R (still no cooling while printing this part. It is important to clean up the airchamber.
I also had to cut some drips away at the top hole where the PEEK is nesting.

I only used 2 bolts to fit the fan to keep the weight down

STL file is: J-head-fanmount-v1.2c.STL
Download file

I printed the part in ABS. In the end the cooling proved enough to keep the lower ring from deforming/melting as it hugs the PEEK to keep the
chamber stable during sidemotions. and stop the down flow of air towards the hotend.

I had to scrape All 3mm holes with my leatherman (could use a drill) and unfortunately had to use a plier to hold the bolt at the flange to fit the fan.

below the tools I needed to set it up.

I hope you like it....
Re: J-head Cooling solution
March 28, 2013 05:45AM
i would recommend to remove the kapton tape, why cooling the peek on the one side and on the other side isolating it under kapton with the heat block, it is a little difficult to just use the kapton on the heating block, due the heat the glue will became week
Re: J-head Cooling solution
March 28, 2013 05:57AM
I did not know capton was good at insulating, thought it was just heat resistant tape...

Removed it and put some extra around the heating block! smiling smiley
Re: J-head Cooling solution
March 28, 2013 07:30AM
actually you want the end near the nozzle to be as hot as possible. kapton tape around the hot part of the hot end is a good idea, and reduces stress on heating elements or resistors as they need to work less. kapton keeps its strength as well under load at the working temperature.

also it may be best to modify the design to allow air to vent upward toward the x carriage, this is the next week spot as far as thermal stress goes. keeping the x carriage cool will prevent warping and cracking of pla or abs.

i see your base of x carriage is pmma. it becomes bendable around 100deg C and reaches glass transition around 105deg c. so keeping it cool is a priority. other than its density from being a complete solid part, it is similar to abs.

Edited 3 time(s). Last edit at 03/28/2013 07:39AM by jamesdanielv.
Re: J-head Cooling solution
March 28, 2013 09:12AM
OP, your hotend lacks the all-important milled vents. Without these it's not really a j-head, it's a poorly fabricated knock-off.

It's not surprising at all that you have issues with heat climbing up the PEEK tube without those vents.

Also, I think you are constricting the duct exit too much. This will cause the fan to stall and move significantly less air. I have had this issue with a couple of ducts I designed.
Re: J-head Cooling solution
March 28, 2013 09:24AM
crispy1 Wrote:
> OP, your hotend lacks the all-important milled
> vents. Without these it's not really a j-head,
> it's a poorly fabricated knock-off.

There are several versions of peek holder and cooling groves were used only since version 4. So absence of cooling groves alone isn't proof that this particular nozzle is "poorly fabricated knock-off".

See j head nozzles.
Re: J-head Cooling solution
March 28, 2013 09:49AM
I now hope my knock-off is made of PEEK and not some other cheap material.

I have set the exit area at 2/5 of the inlet area and a small volume for some tiny pressure buildup.

the fan is taking power from the heater and not running at full speed.
When running there is a nice draft behind the PEEK tube (wet finger test)

it takes the heatblock 6 min to go from 22C to 260C
The top of the PEEK reaches about 50C at 260c
(but I don't know if these figures are good, bad, or ugly)

Edited 1 time(s). Last edit at 03/28/2013 09:52AM by DesignSmurf.
Re: J-head Cooling solution
March 28, 2013 09:51AM
Miso, I like the one with the BMW boxer engine smiling smiley

Edited 1 time(s). Last edit at 03/28/2013 09:53AM by DesignSmurf.
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