Fire hazard concern

[Gandou56]

Allright so I'm a little concern about the probability of the hotend, pololu driver and hotbed to overheat.
Since I don't own a printer yet, I'd like some advice on the installation/wiring i plan to do.
(it's just a matter of making a kind of conclusion on what i've read on the forum and reprap wiki so far)

For the hotend:
- the two resistor wraped in foil so they will hold in the hot end
- use crimp lug for the wiring of the resistors and thermistor
- 18g wire (wouldn't 16 be better since the current seems high for parallel connection ?)
- thermistor also wraped in foil (maybe gluish high temp silicon stuff ?)
- cover the whole thing in kapton tape so the parts will remain in place
- add a switch and fuse/breaker on the line for direct protection and isolation

For the hotbed:
- 18g wire (wouldn't 16 be better ?)
- add a switch and fuse/breaker on the line for direct protection and isolation
- it seems like i must not print directly on the hotbed and need a medium like glass/acrilic/etc. (Which one is recommended and why ?)
- cover the medium with kapton tape for the print material to stick better

For the pololu drivers (with ramps board):
- add a heatsink on each chip (but where to buy those ?)

Ok so that should be it ...
I'm ready for your comments.

Just for the benefit of everyone, i'd like to share with you a small project I'm currently designing that would add some "safety" and usefull features to the printer.
I will add an interlock system to the hotbed and hotend, based on an Atmega328p burned especially for this job, with two thermocouple and associated real time display for direct temperature reading, all of this completed with communication between the interlock and main arduino for emergency shutdown in case of overheating or if the thermistors disconnect. Lets not forget the big red emergency mushroom pushbutton.
Brainstorming still in progress.

Thank you for your advices.

[michaellatif]

Hey Gandou56,

Here are some answers to some of your questions.

For the hotend:
- use crimp lug for the wiring of the resistors and thermistor
<Mike> Soldering work, but the crimp lugs work better. I use the soldering method with the anticipation that I may need to go back and repair the connections, but this hasn't happened yet. The trick to soldering is to make sure the joints don't touch the extruder housing.
- 18g wire (wouldn't 16 be better since the current seems high for parallel connection ?)
<Mike> Yes, but 18g wire works well and I have had no issues with it
- thermistor also wraped in foil (maybe gluish high temp silicon stuff ?)
<Mike> The foil is not needed, just put in the hole in the extruder and use whatever adhesive you want to hold it in place, like many of us have expierenced, you will need to do this or you will face an extruder melt down.
- cover the whole thing in kapton tape so the parts will remain in place
<Mike> This is not necessary, but I find it helps hold everything in place. I wrapped my extruder housing in Kapton tape and it makes it easier to clean and assures me that the thermistor doesn't move.
- add a switch and fuse/breaker on the line for direct protection and isolation
<Mike> I don't think this will be necessary, but you can add it for over current protection I suppose.

For the hotbed:
- 18g wire (wouldn't 16 be better ?)
<Mike> Same as extruder, 18g will work just fine
- add a switch and fuse/breaker on the line for direct protection and isolation
<Mike> Same as extruder, not necessary, but can be done
- it seems like i must not print directly on the hotbed and need a medium like glass/acrilic/etc. (Which one is recommended and why ?)
<Mike> Yes, you will need glass, I have been using glass that I have scrounged from flat bed scanners, but others have been using glass from McMaster-Carr or LHS. The source is up to you, the benefits to McMaster-Carr's glass is that it is meant to be heated and cooled repeatadly, without it breaking. The other stuff has the potential of cracking or breaking, BUT I haven't noticed it.
- cover the medium with kapton tape for the print material to stick better
<Mike> I used to do this, but it was a total PITA. I started using the ABS/Acetone trick with ABS printing. With PLA you will only need blue painters tape.

For the pololu drivers (with ramps board):
- add a heatsink on each chip (but where to buy those ?)
<Mike> I use the heatsinks from http://ultimachine.com/content/heat-sink-63mm-x-48mm

[Polygonhell]

On the Kapton tape on the bed thing, I agree it's a pain in the ass.
You can use PET tape instead, which is orders of magnitude less hassle, but ABS doesn't form as good a bond with it as Kapton and PLA doesn't adhere very well to it at all.
I've also been using "ABS Juice" (ABS disolved in acetone) recently for ABS prints, I use a very dilute solution on top of the PET tape and it's worked very well for me.
There is a lot of discussion right now over on the reprap forums about using diluted PVA glue as a medium for PLA, I haven't tried it. Some people seem to get good results from PLA directly on glass with a heated bed, but it was way too inconsistent for me when I tried it.

[michaellatif]

On the Kapton tape on the bed thing, I agree it's a pain in the ass.
You can use PET tape instead, which is orders of magnitude less hassle, but ABS doesn't form as good a bond with it as Kapton and PLA doesn't adhere very well to it at all.
I've also been using "ABS Juice" (ABS disolved in acetone) recently for ABS prints, I use a very dilute solution on top of the PET tape and it's worked very well for me.
There is a lot of discussion right now over on the reprap forums about using diluted PVA glue as a medium for PLA, I haven't tried it. Some people seem to get good results from PLA directly on glass with a heated bed, but it was way too inconsistent for me when I tried it.

Hey Polygonhell,

I print directly on the glass with the 'ABS juice'. No kapton tape or other medium between the ABS and glass. Sticks well and with the heat up properly I don't get warping or curling.

[Polygonhell]

Yeah I just happened to have the PET tape on the bed, when I thought I'd try ABS Juice, with just the PET I still see very large prints warp and pull up off the tape occasionally, I've had good results with the combination, and I'm loathed to mess with a good thing :p
At some point when I pull the tape off I'll try just the ABS Juice.