Monday, 30 March 2009

I love ABS

I took delivery of some ABS just before the weekend and I have been running the repstrap for about 6 hrs a day since- what super stuff!

Having worked with HDPE for a long time the major problem was warping of any print. ABS nearly cures this although it smells a lot worse. I am now extruding onto a glass chopping board (heat resistant to 240 degrees ) and evostick.

The first major break through I got was reducing the extrusion rate. This had been puzzling me for a long time as every extrusion seemed to have an excess of plastic. I kept recalculating the and measuring the rate it was laid down at and the size but nothing seemed to work. Then after watching for a long time I noticed that when making small movements the machine never got to full speed- should be 720mm/min but on the on screen display I only got 2-300 mm/min- hence too much plastic! I now need to maximise the acceleration on all my steppers using the EMC set up programme.

I have also programmed the arduino so that when it switches off it goes backwards fast briefly and when it switches on it goes forward 1.5 times the reverse quickly to stop ooze and this seems to wok really well (although it stretched my limited programming capability)

The first thing I printed was Adrian's pinch wheel extruder. (I would show pictures but there are no batteries in my camera I will add them tomorrow). This came out really well and appears to be quiet strong- not quiet at Nopheads quality but good enough for now.

I then decided to print the wine glass as we were going out to a dinner party. Unfortunately the machine does not have enough height so I managed the stem- it looked great and only took 40 minutes. When I showed it to friends they did not understand the rep rap excitement. In fact Alex told her boyfriend Steve "Its a good job he already has a wife or he would stand no chance!"

I am now in the middle of printing a large assembly- it has been printing for over 9 hours now and is looking good despite the various breakdowns.

Next steps
1. Tidy all electronics/wires up.
2. Make sure the feed to the pinch wheel is constant using smaller hooks this appears to cause the pinch wheel jams
3. Fasten the extruder more securely to the machine
4. Fix the acceleration issue
5.Move the whole thing into the garage to reduce noise and smell
6. Increase the z axis movement

Questions to anyone

1. What is the biggest thing that anyone has made?
2. Using a pinch wheel extruder and the resistor/brass bar/welding tip/stainless set up could we just wack in solder and extrude it- what is the melting point?
3.Is acceleration an issue on Darwin?



  1. 1. This is the biggest thing I have made It took about 7 hours and has some cracks due to warping. I haven't seen anybody make anything bigger. Even with ABS warping starts to become an issue with large objects. PLA and PCL warp less than ABS.

    2. Tin/lead solder is 183C and lead free about 230 IIRC.

    3. Darwin does not use acceleration. The pull in rate of the steppers is less than the extrusion rate so it can start instantly.

  2. Thanks for the reply Nophead. Half term is coming up so I will try and extrude some solder as it well within the range of the nozzle.