Black SF Shrinkage?

Discussion in 'Technologies and Hardware' started by mgrynberg, Feb 1, 2011.

  1. mgrynberg
    mgrynberg New Member
    Hi all,

    So I'm trying to finalize my panoramic film camera parts, and I'm wondering about shrinkage...

    As I understand the SLS process, the machine melts plastic powder to form the object.
    I read somewhere that WSF (thus BSF) minimum detail size was 0.2 mm, but I also read somewhere that models shrink 2-4% (2009 reply from crsdfr about tubes and holes &).

    So here's the question:
    If I have a fairly big model - say 20x8x5cm - that I want to print in BSF, will it shrink?
    In other words am I gonna get something that's 2-4% smaller - in which case it basically won't work at all since non printed parts won't fit- or will it be that exact size +\- 0.2mm?

    I'm worried because I'm about to order about $500 worth of stuff... I would hate to receive unusable parts... And each part it too expensive to order just for test...


  2. mgrynberg
    mgrynberg New Member
    Just a quick update to this...
    I had a test part done a couple of weeks ago and I measured it when it got home, the dimension that I measured was bang on, so I stopped there...
    Yesterday I measured the other dimensions and one was off...
    It was 6.9cm instead of 7cm. That's way more than the 0.2mm tolerance that's stated on the website...
    Now I'm worried...

    Any clue?

  3. crsdfr
    crsdfr New Member
    I hadn't visited in a while, and I just happened across your post. Funny coincidence.

    I really should delete old posts like that where I don't fully explain things. Yes, SLS Shrinks. Its not something that you (the customer) have to account for. It is entirely the technicians responsibility to ensure the machines tolerances are correct through the continual fabrication and precise measurement of calibration parts.

    That said. Tolerances do stray sometimes, and if the part exceeds these, well you'd be well within reason to talk to shapeways about having a replacement made.

    My previous post there is a bit of a mess, but what I seem to be referencing is that the SLS process becomes a bit complicated in that sub-mm range. We start to encounter the "bleed" and laser spot width considerations of the process. Its not really relevant to your concern here.
  4. mgrynberg
    mgrynberg New Member
    thanks for your reply, much appreciated :)
    I just hope things work out...
    I've spent lots of time refining my model and I can't afford test prints... it has to work...

    Since the model is made of 3 main parts that have to precisely connect (i'm printing a camera), what would you suggest?
    - printing them one by one to be able to check them and adjust the other parts accordingly
    - print all in the same batch so the conditions are consistent and the pieces may be assured to fit like in the model

    Or in other words, do I have a better change of having the pieces all precisely fit if I print them in the same batch?