What's the fire cement and the copper jacket for?

I have been reading the Thermoplast Extruder Version 2.0 and planning to build one for RepStrap. I have minimum access to power tools and so far I am trying to [A] avoid any mechanical work except for assembling, or if unavoidable send the design to workshop...

My question is, what's the fire cement and the copper jacket for? Are they crucial in the design? Is that only for insulting the heat from the air?

Without them, would that work despite of, may be, taking a longer time to heat up...
Or would that work with the cement but without the jacket?

Thanks.

The fire cement is there to hold the nichrome wire in place, and tightly coiled around the barrel. The copper tube just holds the thermistor, I think.

Actually, instead of the fire cement, I'm using a silicate-based high temperature glue (up to 1200C, even in open flame) used for exhaust repair in cars, heating furnances etc. It cost mere 15PLN (5USD, 4EUR, 3GBP) for a 70ml tube (~10ml is needed for a single extruder) in a hardware store. It's much, much better than your average fire cement. Easily formed and shaped after application, dries to an extremely hard and durable shell (obviously, it's designed to withstand very high pressures present in many exhaust lines), doesn't crack at all and can be applied in several consecutive layers or one thick layer at once. This means you can coat the barrel first, then wind some nichrome wire onto it, then put a next layer on that to hold it in place, and finally embed a thermistor in the final layer. For added performance, wrap everything in a piece of mineral wool.

... search for "Prestogum" in your local hardwarestore - it's the same silicate-based stuff but limited in the datasheet to 700 Centigrades max. temp.

Viktor

The copper housing is used to prevent that pieces of fire cement falls off the extruder.