Wednesday, August 06, 2008


Extruder Experimentation

Hello, everyone:

I've been following RepRap for a while. Like Brendan and NopHead, I am a cnc hobbiest, and last year converted my 3-axis mill to cnc. I started following reprap with the idea of adding an extruder head to my mill. I'm basically following the "EmcRepStrap" path.

I've made enough progress on my extruder, though, that I thought I'd share my experiences with the group in case someone else finds them useful.

Starting with the RepRap extruder, I wanted to make a few modifications/goal adjustments:
  1. I'd like to run reliably at high temperatures
  2. I'd like to use an off the shelf heater
  3. I would like to be able to "grow" into high accuracy and higher feedrate

Last week I finally finished and tested my first lashup-- it fed about 3ft of filament quite nicely so i've started configuring my EMC machine so i can start making some profiles. I'm very excited.

A couple of extra pics. The first shows the extruder block and barrel. After experimentation i found that a shorter heater would be ideal-- a 3" barrel was just too long.

This one shows the v-groove rings and skate bearings. This concept worked very well. Though you have to have a lathe, the rings are easy to make, and eliminate springs and such. ( It does take a bit to get the adjusting right though )

Some key features:

Extruder Drive


My plan is to treat the extruder as a rotary axis in EMC, and to control the extruder with a python-based HAL module and pyVCP Axis plugin, what i'm working on now.

The photoset is here:

Forrest has pointed out already that the gap between the last roller and the filament entry point is a bit long, which is true-- I'll fix that but for now if it works dont mess with it , right?

I've noticed a few good things and a few bad things about this design so far:

I make progress very slowly cause of my day job and family, so you probably wont be seeing prolific posts. However, i'm happy to answer questions or certainly welcome your ideas!



The bad thermocouple readings probably arise from the cold junction not being stable. Always keep in mind that a thermocouple measures the difference in temperature between the hot and cold junctions, and not an absolute temp.

In order for this to work reliably, you should probably route the thermocouple wires (no extensions other than with the same TC wire!) to a junction block located in some place where the temperature is constant (i.e. room temp).

Good luck, and keep up the nice work.
cool work!

i love seeing experimental designs like this.

do you happen to be using the RRRF boards? we make handy PCBs for both the AS5040 chip as well as the AD595 thermocouple interface chip.

anyway, keep up the good work.
bert: true, though i'm using a MAX6675 cold-junction compensating chip. It calibrated ok against ice water. your comment makes sense given i forgot to list the 6675 in my list :)

zach: i'm using a board of my own design for the controller-- i'm using a bunch o peripherals that are not standard. I probably could use the rrrf AS5040 board but to be honest i kind of enjoy milling my own boards too ;)
"i'm using a MAX6675 cold-junction compensating chip"

I assumed that you were using something like that, but it sure looks in the images like you are changing wire types in mid-air, close to the nut. That would screw up any measurements! ;)
You blogged it! Thanks!
ah.. "no extensions other than with the same tc wire". Didnt catch that. that'd explain it.

I understand now, good point. I'll adjust that and see if that fixes.
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