fan positioning

I see a lot of fans on the j-heads. Some seem to be positioned to blow on the part being deposited, and some seem to be blowing on the PEEK of the J-head. Some look like both are being cooled. It makes sense to me to keep the PEEK cool, at least, but not the heater nozzle. Is one or the other, or both correct?

Edited 1 time(s). Last edit at 03/08/2014 06:14PM by revwarguy.

The one pointing at nozzle is there to cool the printed part and not the nozzle. Cooling the tip of the nozzle is just an unwanted consequence of cooling the printed part around the nozzle.

Quote
hercek
The one pointing at nozzle is there to cool the printed part and not the nozzle. Cooling the tip of the nozzle is just an unwanted consequence of cooling the printed part around the nozzle.

Thanks, Peter, for the reply, but now that I think about it (and not to be argumentative, just curious) why are there fan shrouds on Thingiverse for J-heads to confine the airflow across the J-head's PEEK cooling fins? They say its to keep the heat from reaching the effector plate, or melting the Teflon liner inside - that makes sense, but is it just gilding the lily?

Is cooling for the part being printed required for some plastic and not others? - I see many printing away on YouTube that do not have any fan. If so, could this be done by a fan mounted off of the print head, like to the side of the print table?

Edited 1 time(s). Last edit at 03/09/2014 10:04AM by revwarguy.

revwarguy: Oops, sorry. I misread your post and my response was poor.

Often there are two fans with j-head:

• one cools the hotend itself (its PEEK cooling fins) so that the heat does not creep up the hotend (this prevents deformation of the PEEK part with higher temperatures and hotend jams when filament would be melting too high (in the PEEK part));
• one cools the printed part (that is the one which I though you mean by "pointing at nozzle" (since the other one is not pointint at the nozzle (orifice) but the PEEK lining)).

PLA needs cooling. So you should have some fan pointing at the printed part. The fan can be on the head or an external big one.
ABS benefits from cooling too but you can do without cooling too. When you overdo cooling of ABS you get layer delamination. So you should cool only a bit and just right with ABS (if you cool it at all).

Edited 1 time(s). Last edit at 03/09/2014 11:27AM by hercek.