I don't understand the reason of fans in the toolhead of the Replicator

[funmakerBart]

I have been designing a "clip on'" unit for the Replicator for redirecting the airflow from the fan's to the extruder for cooling. This by turn the fan's 180 degrees, so blowing in the other direction. By clip on design there is no need to disassemble the fans, just clamp it between the space between fan and thermoblock. The clip-ons are changable units for each extruder for an airflow upwards (to not interfere with the print) and one blowing under the extruder carriage to cool the print. The units are on the frontside so it won't affect the X-endstop and the need to adjust the center of the firmware. Pictures attached.

Now I'm looking closer to the design of the toolheads, I don't understand some  of the design parameters of the toohead. Maybe somebody has knowledge about this or sees the logic more.

• the heating elements of the extruder are connected to the aluminium thermoblock. I assume this to have more mass to it so the heating elements are more stable in temperature?
  
• Where are the fans for?:
• Do the stepper motors need cooling? If so, then the system of cooling with two connections through the thermoblock without Thermical pasta is not that great. The fans are not blowing directly to the stepper motors. If needed for the steppers, it was better to place them on the backside, leaving better sight to the filament path.
• Does the thermoblock / heating-units need cooling? And why? they are switched off/on at the desired temperature. 
• Is it for print cooling? Then the airflow is not quite optimal through the openings left between carriage and thermoblock. Also often not wanted given unpredictable airflow and therefore tension/splitting in the larger prints. There are a  couple of designs to prevent this airflow on Thingiverse.
• ore a combination of above?
• Now I understand why it is always difficult to mount the fans. The fans have holes h.o.h 32mm and the stepper extruder/ thermoblock 31mm. Therefore are the spacers to wide -to bridge this size difference- and always disappearing in the holes in the bottom of the replicator. Of coarse fully understandable holes, because they are for...? DDstarkey has made quite a few items to pimp the replicator in technical sense.
• I thought the plastic plate on the extruders also was intended to fasten the extruders that wouldn't make sense. Of course it has to be replaced by Beefed up Replicator Extruder bracked by MangoT21 and DDstarkey to get a lasting connection with the fillament tubes, but it is resting on both the extruders / delrin-unit or cooler, giving friction/tension in that plate as well the need to loosen it when dismounting the fans. Wouldn't it better to mount the extruder bracket solitair with spacers to the thermo block or carriage?
• about the system with the delrim plunger is said enough and of course everybody has to change this to the Minimalistic MK7/MK8 replacement of Whosawhatis / Emett

  
  

Depending where the fans are for, the mounting could be better imo, not only because of the difference in measurements between fans and stepper motor, but also to only give the possibility to disassemble only the unit you want (so: or fan, or steppermotor, or filament drive-unit) and not the whole unit. Each time I'm afraid the connector for the wiring is breaking.

Anybody knows about the absolute requirements / reasons? This also because of the reversing of the fans for the design of the clip-on units I make, by this the fan is not blowing directly but only ' sucking'  air through the coolers which leaves less cooling I think.

Bart

[PropellerScience]

I think the fans are for cooling the long aluminum block to keep the
heat away from the filament so it doesn't collapse before getting to
the heater block. After I made the extruder replacements I saw no
reason for the heat sink so I took it off. Now the fans blow directly
on the stepper motors and filament. So far, no trouble.

[delsydsoftware]

I played around with removing the cooling fans with on my replicator bowden experiment. It's a pretty bad idea. What happens is that the aluminum block soaks up more and more heat until the top of the extruder gets into the melting range for ABS. The ABS expands and locks into the top of the extruder nozzle, causing a really nasty jam that was difficult to remove. It also heated up the ABS carriage for the extruders to a point that would probably make the plastic sag eventually. Also, the stepper motors do receive some cooling from the heatsink/fan, so they will likely get very hot.

To give you an idea of how much heat is transferred by the aluminum bar, with one extruder on my dual extruder heated to 230C, the other extruder got up to 120C just from contact with the uncooled aluminum bar.

[funmakerBart]

I uploaded the design of the clip-ons for the fans of the Replicator on Thingiverse. So more experimenting with air / hairspray / big ABS prints..

http://www.thingiverse.com/thing:34990

Bart

Op vrijdag 16 november 2012 22:33:05 UTC+1 schreef delsydsoftware het volgende: