dimensioning of sprues

Discussion in 'Design and Modeling' started by pfeiffer stylez, Oct 8, 2011.

  1. pfeiffer stylez
    pfeiffer stylez New Member
    Like lots of other people, I have a couple of small models which became very expensive due to the new price structure.

    [​IMG]

    I want offer them in groups of four and six turrets per file.

    I use small "connectors" to create one big structure.
    Those connectors should be easy to remove, but solid enough to avoid problems during the production.

    [​IMG] [​IMG]

    Question:
    Are my current connectors capable to ensure an unproblematic printing and cleaning ?

    (btw, all pics are clickable thumbnails)

     
  2. stop4stuff
    stop4stuff Well-Known Member
    You might have a rejection notice if the models are ordered in White Detail (1mm min walls)... and you might have a failed notice in FD or FUD as 0.3mm is very fragile & the turrets would probably seperate during handling or cleaning.

     
  3. pfeiffer stylez
    pfeiffer stylez New Member
    Mhh... since they're 1 mm deep, they should be conform with the minimum wall thickness rule for WD.

    But how thick (or, in this case, high) should the predetermined breaking points be to survive the production process ?
     
  4. stop4stuff
    stop4stuff Well-Known Member
    1mm WD wall thickness applies to walls in all directions, your breaking blocks might be 1mm deep, but they're only 0.5mm tall, and 1mm in WD is more fragile than 1mm in FD or FUD.

    For the break point, the best bet would be to email service@shapeways.com and ask for 'official' opinion.
     
  5. aeron203
    aeron203 New Member
    I noticed your design is notched in the middle to make it easy to break away, but I think that might happen earlier than you want it to. Most sprues and stems I see have a thicker body and taper at the end. That way it will be easier to remove all of the unwanted material. I would not go below 1mm anywhere.

    Picture your model swirling around in a cleaning bath or in a pile with dozens of other models on top. If the group breaks apart it could create a problem with the order, so it's worth the extra material to make sure it works.
     
  6. woody64
    woody64 Well-Known Member
  7. pfeiffer stylez
    pfeiffer stylez New Member
    Thanks guys. :)
    As first effort, I'll make predetermined breaking points thrice as tall as they are now.
     
  8. GWMT
    GWMT New Member
    Try to make the surface area where the sprue merges into the model surface as small as you can. I've been successfully using a 1:1.5 or 1:2 ratio for length/width where 1=minimum wall thickness for the material.

    Using an L-shaped profile for the sprue instead of a square or round shape will reduce the amount of material used in the sprue by 50% but will still give you the same stiffness as the larger shape. For short/ intermediate distances an angle shape of minimum material thickness that's 4 or 5 times as tall/wide as the minimum material thickness works well. Most of the sprues in this example (for FUD) are 1.2mm x 1.2mm angle 0.3mm thick.

    CN Switchstand on sprue-detail.jpg

    I like to taper the sprue down towards the model surface or use a disc shape for the sprue to force the cutting blade against the model surface and reduce the amount of sprue left on the model after cutting. I also use flush-cutting tweezers like these examples from Micro-Mark and Intermountain:

    http://www.michtoy.com/item-MCK-82393-Sprue_Cutter_Despruing _Tweezer.html

    http://intermountain-railway.com/bandb.htm

    They concentrate all cutting forces on where the sprue meets the model surface so the model can't twist and break as you're cutting it free. They're worth every penny spent.