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UM2 bowden block cooling improvement

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Half of the 25mm fan output is useless on a single-extruder UM2, so while I had the hot-end apart to replace the temp. sensor, I made a small piece of sheet-metal to deflect the second-extruder airflow toward the left-side single extruder.

The two left-most and right-most slots of the vertical piece are not in front of the fan, so blocking them is irrelevant. I used the second slot from the right.

I just cut a small rectangular piece of sheet aluminum and sanded it down to slide-fit into the second slot at the right end of the vertical piece that holds the top and bottom plate together. It's about an inch by a half-inch. See images below.

It is wedged in place by the screws that hold the top/vertical/bottom pieces together, which intrude into the second slot from the right.

After inserting and tightening the top and bottom screws, I bent it toward the left, where it directs most of the output from the right half of the fan toward the bowden stop - it does a better job of cooling the teflon block and the cold filament inside.

otherother1

 

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It still cools the heatsink, just not as much on the cooler part of the heatsink at the right. That's why I left a gap at the top and bottom of the deflector. Cooling the parts near where the heat is generated is more effective than cooling the heatsink an inch away. If this was an issue, dual extruders would be problematical. The tweak just uses some of the airflow that could otherwise cool a second extruder.

The deflector is about 1mm thick, and is held in place by the two screws that attach the top and bottom plates to the slotted vertical plate. The tips of the screws intrude into the second slot, and wedge/clamp the deflector plate in place quite firmly.

 

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Hi,

Just thinking out loud without knowing more accurate:

At the end of a print job, the amazing power of this small cooling system is very noticeable and the temperature drops very quickly. I think optimization is needed more elsewhere.

The deflection plate probably shows some effect, but:

Deformations of the ColdEnds are mainly inside the direct transition area for HotEnd. The Teflon material is probably a very good thermal insulator, and a cooling air flow shows only delay its effect.

Maybe a ColdEnd from ceramic material would be optimal.

Markus

 

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http://www.2engineers.com/shop/ceramic-hotend-chess-for-1-75mm-fillament/

Note: it needs a PTFE liner for PLA, as Daid points out. Also, "When using the hotend with PLA please use a small fan for cooling the barrel."

 

Bottom line on the tweak: can't hurt, costs nothing but a few minutes, apparently extends the life of the plastic collar indefinitely - mine now has over 2000 hours on it without replacement.

 

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It still cools the heatsink, just not as much on the cooler part of the heatsink at the right.

 

I would expect temperature difference to be quite small between left and right as the heatsink is quite massive and made from aluminium which is not the worst thermal conductor...

 

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I'm trying to cool the PTFE barrel better, not the heatsink.

Note that I left a slot at the bottom of the alum deflector, to allow some useful air to flow over the lower heatsink. The air that is deflected toward the barrel wasn't cooling the heatsink anyway - it was moving on past it one cm above it, and providing no cooling to the heatsink whatsoever.

Since there is no dual extrusion, and won't ever be, with this head design, there is no reason to waste the cooling that can extend the life of the isolator indefinitely.

 

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... Cooling the parts near where the heat is generated is more effective than cooling the heatsink an inch away.

I'm not entirely convinced of this statement. Given the size of the back fan and CFM (aprox 2.2~3), it would have an easier time cooling an inch away from the heat source rather than blowing directly on it. Heat always travels towards cold. By easily cooling the heat sink an inch away, it gives the heat somewhere to run to, away from the hot end. Trying to reduce the heat directly at its source with such a small fan wouldn't be that effective and doesn't give the built up heat anywhere to go, so it just stays there.

I'm not saying your deflector doesn't work, just that the statement made me wish I had some sort of Flir camera to see the difference. Better still, I wish I could perform heat analysis on the whole hot end assembly to see which is better: blowing on the hot end directly or an inch away down the other end of a heat sink.

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