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Re-using Hot end cooling air to cool object?

Posted by HugoW 
Re-using Hot end cooling air to cool object?
August 10, 2017 10:12AM
Hi,

I have an MK8 Extruder J-head Hotend, something like this:



And I have no object cooler. I am considering to replace the current fan and screen with a solid plate, and place a radial fan on top of the heat sink. So the air blows through it. I think this will be more effective as the centre of the current fan, as on the pic, covers a large area of the heat sink without moving air over it. Would the air coming out of the bottom of the heat sink still be cold enough to be redirected and used to cool the object while printing? It would save a second fan.

Does this make sense, was it already tried? I cannot find it.

Cheers,

Hugo
Re: Re-using Hot end cooling air to cool object?
August 10, 2017 01:08PM
Setting the heatsink that way is a mistake many noobs make when assembling that type of extruder. The air exiting the heatsink blows on and cools the heater block and you get extruder jams because the heater can't stay hot enough to keep the filament melted.

Print cooling is best done using a dedicated fan driven by a PWM output from the controller board. Slicer's allow you to control the speed of the fan depending on what part of the print is being printed.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Re-using Hot end cooling air to cool object?
August 10, 2017 02:37PM
I currently do this, it's not perfect, but it does work. I have to do some modification to the design i made to increase air flow to the print still, but i also routed air to blow across the top of the throat which has significantly reduced jamming.
Re: Re-using Hot end cooling air to cool object?
August 10, 2017 04:17PM
It is certainly possible but it's a compromise. PLA will be more difficult as you cannot control how much part cooling there is as the hot end always needs cooling to stop jams. The first few layers will be cooled and may effect adhesion of nearly any material.

You could stop printing PLA. Abs needs minimal layer cooling, and does not jam in the same way from heat creep. Would a pwm fan on the cold end effect extrusion properties? That I'm not sure about.. My best guess is altering cold end temperature would effect amount of molten plastic, thus affecting retractions.
Re: Re-using Hot end cooling air to cool object?
August 10, 2017 04:32PM
Thanks for the input. I plan to use PLA a lot, so I'll use separate fans. I'll mount the heat sink 90 degrees from it's current position to avoid air from the heatsink / fan interfearing with the air cooling the print. Is the PWM fan control something standard in Marlin?

Cheers,

Hugo
Re: Re-using Hot end cooling air to cool object?
August 10, 2017 05:10PM
The RepRapPro Ormerod 1 used a single fan. The exhaust air from the heatsink was ducted to cool the print. It worked tolerably well, but not as well as a dedicated print fan does. See [reprappro.com] if interested.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Re-using Hot end cooling air to cool object?
August 14, 2017 09:55AM
I made a design for the smartrapcore which ducted air from a 40mm heatsink fan to the print, and had a little shutter to close when printing ABS instead. Worked better than no print fan but not as well as DC said above as a dedicated twin fan (or single fan into a ring diffuser would work). [www.thingiverse.com]


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Re-using Hot end cooling air to cool object?
August 15, 2017 06:00AM
Quote
HugoW
................ Would the air coming out of the bottom of the heat sink still be cold enough to be redirected and used to cool the object while printing? It would save a second fan.

Does this make sense, was it already tried? I cannot find it.

Cheers,

Hugo

I have used the air from the heatsink for several years as the main cooling for small PLA prints. Photo below shows a very old (5 generations ago) and the first thing of note is the bloody great block in front of the fan shroud - this works MUCH better than a streamlined shroud. The ugly great block of the heater/insulator caused the air to burble around and cool the print from every direction.



The two brass tubes were not so great and were replaced with a ring around the nozzle.

Mike
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