Thursday, September 27, 2007


Running smoothly - for 5 minutes

I think I've got the PLA extrusion fixed. This is my setup, complete with little G-clamp to add additional pressure. I'm using a massive "that's not a motor - this is a motor!" 12V motor frankensteined on to the standard gearbox using CAPA. I left the fan from the little motor there in case the CAPA decided to get warm...

The extruder now purrs like a kitten with no feed issues whatsoever. The extra switch (red DPDT above large fan) is so I can switch the thermistor between the controller and my meter when calibrating.


My extruder heater just went orange and popped - just after I sent my spare to Adrian! No, Adrian, don't rush it back - I need to build another anyway :) Still, it goes no more. Fair enough; it's an elderly specimen and I can do better. I also know to use a 20% lower resistance than specified for the standard extruder heater, as it won't quite work with PLA on a real 12V supply (it needs 14V).

A small bit of background: It's made from "pelican wire" without secondary insulation, if I recall correctly. I checked with a multimeter and it's not a short to the barrel. Might have to go back to BBQ paint and standard wire for PLA.

Vik :v)

I used bare nichrome and JBWeld for insulation:

It seems to have held up well so far, several hours at 200C.

What are the advanges of PLA compared to say HDPE which seems easier to get hold of?
I believe PLA is used because it is a renewable resource (corn starch or sugar cane), and is biodegradable.

As far as I am aware, HDPE is typically made from petroleum reserves, and is not biodegradable.
Are you using the TIP110 as your heater driver? If you are trying to squeeze some more power out of the heater controller you might try replacing it with a MOSFET so you would not loose ~2 to the transistor.
Why borrow trouble? When we truly start to run out of oil, HDPE will become too expensive.
From what I understand the production price of oil worldwide is still just a shade under $10/bbl. The rest is markets, politics and just plain greed. :-)
PLA IS very rigid, and to be honest I have nigh on a kilometre of the stuff so it's what I'm using for the foreseeable future.

I like it because it doesn't warp as it cools, it looks nice (aesthetics are important) and it is not too readily melted or bio-degraded. If you think about it, bio-originated plastics lock up carbon, so why make them degrade?

I'm using a TIP120 as the heater driver - more current than a TIP120. I know how to use them and they're cheap.

Vik :v)
Blah. TIP120 passes more current than TIP110. Wake up Vik.

Vik :v)
Could the failure be in any way related to the amount of current or power dissipation per unit length being too high (too hot)? That was the reason for suggesting a MOSFET, it would allow for a longer heater wire with the same or greater total power and less current.
12V/8Ohms = 1.5 Amps = 18 Watts
10V/6.2Ohms = 1.56 Amps = 15.6 Watts

In any case I hope for a long productive life for the new heater.
On seeing the "TODO" about nozzle insulation, I wondered if you guys had come across some stuff called "Nansulate".

This stuff is supposed to have astounding insulative properties in a coating 5 thousands of an inch thick. They do a range of industrial and domestic formulations (for insulating pipes, etc). I just wondered if it might make the extruder heater more effective for less current.

I'm considering acquiring some to paint my ceiling with. If it does what it says on the tin, I'll be mighty impressed.

The demo video on their website is impressive - it shows a metal plate on a gas hotplate. They drop water on it. The water on the uncoated half boils away. The water on the coated half doesn't.

While it isn't exactly "from scratch" to be using highly manufactured nanotech coatings, it's not something that would be scarce - they sell it in five gallon drums.
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