Monday, 22 September 2008

Going green

Getting a bit bored of natural ABS, which is cream coloured, I ordered some black and some green from New Image Plastics in the USA. Despite the high cost of shipping it still worked out cheaper than buying it in the UK. I chose green because it should be easier to photograph than black or white and it the RepRap logo colour.

I was surprised to find that it does not behave the same as the natural that I got from the RRRF. It does not seem to stick to itself, or to the base material, as well as the RRRF ABS did at the same temperature. I have raised all the temperatures by 15°C and, although it is better, I think it still needs bit more. It's appearance is more glossy, so that might account for it being less sticky, or it may just have a slightly higher melting point. I have no idea if the green dye has an effect or whether the base ABS is different. It will be interesting to try the black.

I made a new version of my screw top pot in order to perfect the thread before posting the STL files on the RepRap Objects wiki. It turned out to be nightmare to get it to print. Besides the problem of it not sticking to the bed, my extruder kept breaking GM3 gearmotors, but that's another story.

The ABS version came out about 1mm bigger in diameter than the HDPE version due to lower shrinkage.

I modified the thread to make it easier to start. The original thread started abruptly at the top of the pot and the bottom of the lid. I modified it in CoCreate by continuing the helix past the top of the pot and then milling it back to 2mm below the rim. I did the same to the lid's thread. That allows the lid to overlap 4mm before the threads engage, making it easier to line up. The thread now tapers out to a thin sliver to make it easy to engage. The result works a lot better than the previous attempt.


  1. Hi Chris,

    Green looks great! I've read a paper about the dye always affecting the material properties of the virgin plastic. It's not necessarily bad though, but something that give new options but adds some complexity. I looked for the article, but I guess I never saved it.

    Thanks for taking the trouble of uploading the design.

  2. Brilliant work, as usual, nop! :-D

  3. Not related to this post, but I figured it might go un-noticed if I commented on the appropriate post.

    Does your firmware/host software ever use the microstepping that your stage is capable of? Just curious...

  4. Hi Robert,
    I get an email if you post on any article so it will get noticed.

    Yes I use x10 microstepping on my XY table. I have no choice, because the controllers only have step and direction inputs. I don't need the 0.006mm resolution that gives but it does make the motion very smooth.

  5. Hey, Nophead:

    What formats can CoCreate save? does it create decent STL or do you find that you have to post-process the STL with meshlab to fix holes and such?

    I am using an old ( 2003 ) version of solidworks that i had while a student. it creates awful STL. but it is great software in terms of creating models.

    How do you like CoCreate? can it save STEP files? Enrique and I have been talking about ( among other things ) trying to get skeinforge to handle STEP AP203 files which would be more accurate and efficient than STL.

  6. Hi Dave,
    CoCreate Personal Edition (the free one) can only save in its own format and export STL and VRML. It can only load its own format plus STEP, IGIS and MI.

    I have never had any problems with the STL it produces. It continually monitors for non manifold shapes and refuses operations that would make them.

    I find it very easy and intuitive to use. It takes a long time to start up but I can't find much else to criticise.

  7. Very interesting info-- i think i'll give it a try, if it creates Solid STL.

    Solidworks is really really awesome, and imports exports just about everything, but is also a billion dollars :(

  8. cool work nopehead! as usual :) Your blog was always very inspiring to me.

    I noticed your parts have a nice surface on both sides. We still have problems getting the raft settings right. The raft sticks to the object too much AND the first layer is too thin. So one would have to increase the extrusion rate at the first layer (although then it would even be more difficult to seperate the raft) but we cant figure how to do it with skeinforge. There does not seem to be a parameter yet. Do you manually or automatically edit the gcode files after the come out of skeinforge or do you just have the right raft settings?

  9. I haven't tried the raft facility in Skeinforge yet. Indeed all I use is slice and fill and I remove all the info from the gcode apart for the extrusion paths. At some point I will investigate the rest of the tool chain for combing, etc.

    My raft strategy is detailed here here

    In order to get the first layer neat it has to be at the right height. I currently use the layer height minus 0.1mm. That leaves temperature as the only way to control the bonding.

    After the raft is laid I cool it with a fan for 2 minutes to ensure it is all back to room temp. I then do the first layer at 215C at 8mm/s and subsequent layers 230C at 16mm/s. I add 10C for green ABS.

    If it sticks too much, or too little, I adjust the first layer temperature in 5C steps.

    Also my raft is discreet threads so, even if it sticks fast, I can peel it off one thread at a time with a penknife.