Buiding an extruder

Following Adrian's efforts to build an extruder while I was waiting for a print I decided to have a go- not very succesfully but I think some parts have merit. I

Had some 23 mm ID aluminium tubing and an auger that was 23mm diameter. I put a goove in the top of the auger and then tapped a hole to stop the auger moving up and down.

The pipe is to supply granules to the auger .

The set up moved polymorph down the tube (And up if you reveresed it!). I then added a heated barrell and a 3mm hole and set it going and it made a small lenght of 3mm ish rod but it was very uneven and when I came to restart it from cold a plug had formed meaning I had to take it all to bits again.

Fixing Extruder issues

I have been experiencing the same problems as everyone else with the teflon barrell coming out of the bracket. This seems to happne most when the nozzle hits the work piece and it is extrremelyt annoying especially half way through a build.

I finally decided to fix it once and for all. My solution was to make a stepped piece of teflon

with a larger diameter at the top 22mm, in the middle 16mm and a jubilee clip bit at the bottom 14mm.

This is then placed into a piece of MDF with a 22mm hole at the top with a 16 mm

hole at the bottom to stop the teflon escaping. The idea of the 14mm bottom bit is to get more grip on the threaded rod so tha that part does not come out.

Black heart

After several hours of checking and changing parameters I have set up to make these hearts.

I found the width that I was extruding at by playing with speeds using a simple g code programme until I found that 150 mm/min onto gaffer tape was the best.(MDF and perspex did not stick and I was not using a raft)

I then extuded several lengths and measured the diameter with a vernier and found that it was 1 mm (the same size as the hole on my nozzle). I put these into skeinforge and then made the extrusion height over diameter 0.9 and these hearts came out.

As they are only 1 layer thick at the bottom there are small holes. To improve this I will make the walls thicker which will force Skeinforge to put 2 layers on.

Making the EMC talk to the extruder(a bit of a bodge)

I am not a computer programmer so I really struggled to make the extruder talk to EMC software.

After a lot of trying This is how I did it- not elegant but it works for now.

I programmed the arduino to cotrol the temperature of the nozzle using a thermocouple and the PMW board form RRRF. I take a signal from pin 8 of the breakout board programmed as flood coolant using the EMC setup programme. The arduino then detects if this is high or low and turns the PMW driver for the extruder motor on and off.

I tried using the spindle on and offf command but for some reason it would not work.

WIth this I then needed to modify the g code generated by skeinforge so that instead of m101 it was M8 wihich was eary enough by using search and replace but because there is a delay in the time the signal was sent and the extruder starting I had to also add G4 P2 which causes a 2 second delay.

So I have to replace
M101 with M8 G4 P2
M103 with M9 G4 P2

M105 with blank
M104 with blank
remove all S commands.

Fiddly but workable.
I now need to work out how tp programme the M codes into EMC. It is possible but so far with my meager skills I cannot see how to do it.

First reasonable prints

Here is my first decent print of Nopheads hearts downloaded from thingiverse.com.

The print quality is Ok but needs some work on getting rid of small holes and lumps and bumps but my daughetrs are pleased with them!

Theyt were printed with 120 deg c using polymorph directly onto an MDF bed with no raft.

About My Repstrap

This blog is to document the development of my EMC based REPSTRAP based on the REPRAP project.

The project uses an MDF frame with comercial bearings and slides on all 3 axes and uses commercial stepper motors and drivers.

The axes are moved by rotating threaded rod with long connecting bolts to drive the plates. These work well and do not seem to have backlash.

The steppers are coupled to the rods using rubber pipe(petrol pipe) and jubilee clips.

The steppers are controled by the free EMClinux CNC programme, www.linuxcnc.org/ .

The extruder is the reprap extruder.

The .stl files are generated by the CoCreate modelling personal edition and then converted to G code by skeinforge.