J-Head Cooling and print cooling - Can you explain please

So my i3 is nearly complete. I'm waiting on a part and meanwhile investigating cooling, and I've ended up a touch confused.

1 - Cooling ramps 1.4 - no problem. Obvious, and I've installed an 80mm silent fan cooling the stepper drivers and blowing away from the bed/head. No problem.

2 - Cooling the print - I've read that with some prints you need to cool your work as it prints, avoiding cooling the actual bed or head, which you want hot. - This makes sense, particularly with overhangs etc. I'm assuming this is the software controlled fan (D9 on the RAMPS) - i.e. the printing/slicing software controls this fan, switching it on where needed? I'm seeing a 40mm fan is the most common choice. Does this all sound right - .?

3 - Cooling the J-head. I've noticed that pretty much everyone seems to have a fan installed cooling their J-head. Some research suggests this is to cool the plastic (PEEK?) part so a) it doesn't melt when printing ABS, and b) so it doesn't jam when printing PLA. Is this right? Does PLA melt so easily that it can soften and block the head before it reaches the metal part? Are 30mm fans the way forward for this? Do you just connect it to permanent 12v? (some seem to piggy back off the heater wires)

Cheers

Roger

1. Ok. I use 2pcs 40mm fans.
2. You're right. Turn it on in the Slic3r settings and it adjust itself automaticly. I have a 40mm fan with a printed a duct, gives better bridges and less "fuzzy" prints.
3. PLA softens at 50C but I never had problems before the fan, but better safe than sorry, specially when printing with high temp so it doesn't creep up the cold end. I use a 40mm fan connected to 12V so it's always on (same wires I use for LEDs).

Here's my setup:
[www.thingiverse.com]

/Roger

Edited 2 time(s). Last edit at 03/31/2014 06:00PM by Devrope.