Shrinkage allowance for Raw Brass material?

Discussion in 'Materials' started by woodsworks, Sep 26, 2013.

  1. woodsworks
    woodsworks Member
    Hi All

    Having much experience in obtaining brass castings of a specific size using 'traditional' method of resin master-to-rubber mould-to-wax-to-casting, I am guessing that we would need to allow for some shrinkage of the Shapeways raw brass material if we are aiming for a particular size? Could tech support please correct me if I am wrong, or enlighten me as to what the shrinkage percentage is if I am right? I am not looking for micro-precision here, just a rough guide - it is usually easier to scale the model up slightly and have to file a bit of metal off later than to have to try to add metal.

    Shrinkage allowance when making brass castings the old fashioned way can be from two to six percent depending on the method used to make the rubber mould. However, for skipping the rubber mould stage, and not knowing if the system might be automatically compensating for shrinkage, the old 'rules-of-thumb' do not apply.

    Regards,
    Paul.
     
  2. etyrnal
    etyrnal Member
    i remember reading that Shapeways compensates for this automatically for you... so far that has not been my experience..

    a ring that i designed to have an ID of 21.00mm, came to me with 20.4mm (approx)

    i'd love to know the answers to this too.

    for each material.

    would the shrink be linear by volume?

    it would seem that through their experimentation, they could give us a table of figures/factors for each material.

     
  3. woodsworks
    woodsworks Member
    Perhaps SW allows for shrinkage of the resin/wax part, but not the brass? When I have made brass castings using the 'cold mould' process, shrinkage is about two percent, which the jewellery casters tell me is the thermal shrinkage of the brass; the dimensions mentioned above, of 21mm shrinking to 20.4mm, is roughly three percent so I am inclined to scale up my CAD design by two percent for SW brass just as I do for 'traditional' brass castings.

    My experience with brass casting tells me that shrinkage is most apparent/most affects the shortest dimension, so a long, thin object will not contract two percent in length, only two pc of its shorter dimension, 'width' or 'thickness', as it were. There is still some shrinkage in all directions, but it is certainly not uniformly proportional.

    Regards, Paul
     
  4. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    The guidelines state ±0.125mm as the accuracy. If you experience anything outside of this range, tell service. Even if you don't require a reprint, it's good for us to know when things aren't up to par.
     
    Yuniyaro likes this.
  5. mmcalc
    mmcalc Member
    I made a brass part and applied a 1.4% scale factor to it, i.e. I scaled my model up. The part was within 1 or 2 thousands of an inch of what I desired with the un-scaled model.
    Mike
     
  6. ChristianH
    ChristianH Well-Known Member
    For a few Bronze castings I've seen shrinkage of ~1.5%.
    Am I actually eligible for a reprint for these parts?
     
    Yuniyaro likes this.
  7. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    We guarantee every print, so regardless you're eligible for a refund. Is that 1.5% less than or equal to .125mm?
     
  8. Shea_Design
    Shea_Design Well-Known Member
    Be careful with reprints, I had a successful cast silver part reprinted (due to odd build lines) and latter found ALL SIMILAR DESIGNS REJECTED. I would have prefered to eat the cost but did end up ordering 20 castings from another service and opening an ETSY shop so I guess it worked out for me. -S
     
  9. ChristianH
    ChristianH Well-Known Member
    It is much more than 0.125mm and it was quite a while ago now.
    Please let me know how to proceed.

    Thank you.
     
  10. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    Ah well there is a time limit on refunds, but shoot service an email to see what they can do.