So McMaster Carr has lot of fun toys.

I looked here http://www.mcmaster.com/#die-cartridge-heaters/=9lfpwf
at the Miniature High-Temperature Cartridge Heaters

The smallest ones are 1/8" in diamater and 1.25" long, available in 25 or 50 watts
only wrinkle is they run on 120VAC.

so... can we take one or two of something that won't stop working when it gets close to operating temperature, power it from a relay? driven by the heater control wires that switches wall power?

i really can't believe they shipped a "mark v" revision without pondering what system operating temperature would do to the components involved, but given my other reservations about the engineering involved, i'm not terribly surprised.

A while back i dabbled in some mil spec design work and the bible of resistor use was MIL-STD-199 which has been superseded by MIL-HDBK-199. Both are available at http://www.everyspec.com/

Contrary to what you might expect, it is actually very useful engineering centric design and application guides. It doesn't just list compliance rules, but actually discusses the pros/cons of various resistor types, derating, load characterization (e.g. sinusoidal, dc, spikey, etc) and how each of these effects the 'quality' and lifetime of the component. It is a foundational element for how to design and quantify the reliability of a circuit.

For capacitors look to MIL-STD-198, superceded by MIL-HDBK-198. It serves the same role for all types of capacitors.

tom w wolf

These seem simular to the McMaster ones but with a wider voltage range. The even have PID controllers for them.
http://www.sunelectricheater.com/

http://watlow.com/ is another source.

Also, googling around for "nozzle heaters" brings up things designed specifically for heating extrusion nozzles.

I saw a few as low as $10 last night. It would require machining a cylindrical piece to replace the rectangular block that's there now but that shouldn't be TOO difficult for us.

There are also heaters with built in thermocouples.

Tons of options.

The nozzle heaters seem to be the way to go. I think our metal lathe is working well enough for the minor machining necessary. One thing though, most seem to need a special controller. Would need to purchase that as well? Any guess as to exactly what nozzle heater we need. Watlow http://www.watlow.com/products/heaters/ht_nozzle.cfm seems to be as good as any and there prices are decent.

js

The heaters I looked at all run on 120VAC (or 240)
We can probably do as Metis suggested and drive it with a relay from the existing control board, unless that's a half fast hack, too. Does the existing heater control have adjustable PID parameters, is it linear, or what?

Another trick is specing the wattage we need. Too low and it won't get hot enough.
Too high and it'll heat up too fast and make the control loop twitchy.

I was pondering whether someone with some social skills could engineer us a sample or two.

Or we get some more nichrome and wind our own again. THAT part of the Mk IV seemed to work, no?

oh i don't doubt that there are times you want to overload a resistor and that you certainly need to know what it'll do when it gets abused, but if dez's math is right as those things approached operational temps their wattage decreased to the point that they weren't putting out enough heat to overcome heat loss to the environment.

now, his math or my understanding might be wrong, but either they shipped a bad 1% accurate resistor which seems remarkably unlikely, or they designed it wrong, which given several other notable lack of industrial design thoughts, seems more probable.

BTW, I forked over $45 for the new power supply. Jon threw down $5 but I'd love to get more money from anyone who anticipates using the MakerBot. 7 more people @ $5 each?

I just put $5 in the donations box with a postit onnit for this.

I wanted to put it someplace safe.

If it's not easy to get it from there to you, let me know.

Thanks for doing this!