Comments on RepRap: Builders: Extruder Heater update

Thanks for the info Nophead, I will try with Fire ...

2009-09-21T08:44:30.297-07:00

Thanks for the info Nophead,
I will try with Fire cement. I suspect that fire cement will not hold the washers so I may end-up
using the cement for heat transmission and welding the contour of the washers together.

I wouldn't use JB Weld because despite what it say...

2009-09-21T06:16:07.425-07:00

I wouldn't use JB Weld because despite what it says on the package it disintegrates after a few tens of hours at 240C.

Nice design, I am going to try this a variation. I...

2009-09-21T05:47:45.832-07:00

Nice design, I am going to try this a variation. Instaid of using the TO220 I want to try a stainless nichrome copper sandwich :)

Nichrome wire with stainless washer on top and copper washer on bottom glued with JB weld. if I am correct most of the heat should be conducted by the copper washer in contact with the nozzle (with thermal compound).

Nice work. I'm also using a stainless barrel (a d...

2009-08-30T03:51:23.414-07:00

Nice work.

I'm also using a stainless barrel (a drilled and reamed bolt) with a heatsink above. The poor conductivity of the stainless does seem to keep the temp at the entrance below melting temp.

Just a random comment. In my experiments with a re...

2009-08-29T20:33:21.740-07:00

Just a random comment. In my experiments with a resistor based extruder, the basic finding is that the gen 3 electronics can take at least 2.5 ohms of resistors with about 4-7 being a good safety region for a minimum resistance. Get any lower and the gen 3 electronics will start to malfunction. Basically the lower your resistance the more heat they pump out, but the more likely the resistor is to burn out. Also, the wattage rating is more of a guide based on the overheating of the resistor. The overheating is reduced if you have more conduction of heat away. Ie a snug fit with an aluminum heat sink will mean the resistor can take more than 5 watts of current(though of course it will eventually pop at enough energy throughput).

Nicely done. The devices aren't really meant to op...

2009-08-29T15:45:15.571-07:00

Nicely done.
The devices aren't really meant to operate at those temperatures. So if they fail over time, here are some that are rated at 10W at 250 degrees Celsius. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=RHRB-1.0K-ND . Sure its not a TO220, but the power derating curve suggests that even their 5W devices are capable of dissipating 10W at 250 degrees Celsius. It may need some insulation wrapped around, to prevent heat loss, but it has a handy mounting tag. Device pdfs are available here http://www.vishay.com/docs/30201/30201.pdf.
Murray Horn.

A nice simple design and it looks robust as well. ...

2009-08-29T14:40:57.633-07:00

A nice simple design and it looks robust as well.

I had dismissed the TO220 resistors because of their low temperature rating but you seem to get away with it.

You can probably fix any tendency to jam by opening up the lower end of the tube with a tapered reamer.