See Rhino file cross_demo.3dm (99.6 KB). The object is less than a centimeter high, and the wires making up the cross have a thickness of just 1 mm. Now the challenge is to arrange several of these objects so:
it is easy to separate them later, for example with a wire cutter, or with a small circular saw,
molten metal can find its way,
the number of sprues needed is minimized.
I first tried it as illustrated below, but the design was rejected by Shapeways: “The amount of sprues and supports necessary to cast this part would make finishing impractical. Metal will not flow freely as currently designed. Pieces should be separated.”
I can’t tell from the drawing but it looks like there are only two unique designs. Why not just upload those and print multiples? If you want them all as one piece I would lay them out in a radial array. That way the molten metal could flow from a central point to all the pieces equally.
They are all slightly different. I need to find dimensions as the pieces are supposed to plug into another system, a toy.
As far as I understand it, there will be a handling fee of about 10 EUR per printed piece. At a material cost of just a few cents, that just doesn’t make sense. I’d rather spend a little time to separate the pieces later.
That looks like it will work as a gating system, but you also have to consider the 3d printing operation. I don’t know that much about 3d printing but they may want something that will support itself and be stable so that it doesn’t fall over while printing.
What exactly is Shapeways doing? Printing a wax pattern and casting it straight?
If yes, the standard in jewelry investment casting is creating trees (don’t know the right English terms, it’s how we call it in Portuguese).
But usually we would print the patterns with only a stump that would be attached to a wax three with hot wax. We’d do that to avoid the 3d printing costs of the three, usually way highier than the cost of the isolated pieces.
So I’d recommend you to print only the parts. Upload it as a multi-part file with separate volumes. No need paying extra for the work they’ll do anyway. Besides that, if you submit it like this they won’t split the tree, they’ll deliver you the complete tree and you’ll have to cut it an finish yourself.
Or are they stating that they’ll interfere with the geometry you send?
Make the main sprue base a conical shape, place the parts pointing towards the thin end of the trunk, like in the picture. Do cylindrical sprues, 2mm or 3mm in diameter for a ring sized part (If the 3d printer material holds - that’ll be try and error). No need to go fancy there, I’ve printed jewelry for ten years and only saw cylindrical sprues the whole time.
I’d keep it flat like you did, it will cut the support printing time & material to a minimum. What you can consider is adding patterns to both sides of the main sprue.
If memory serves me we’d use 3% for a two step casting, silver master pattern and gold product. I’ve seen brass listed as 1.4% so I guess it would be a good start.
It’s a good idea to add a cube with known measures and X/Y/Z axis markings on the face to your test castings, that’ll give you a good idea of what is going on. Sometimes geometry interferes.
This line bellow drove me crazy with the thinner valleys being overstretched too thin by the bigger masses pulling material while cooling. We’d never get the expected thickness and the customer kept pointing his finger at me, that the prints where wrong.
Right you are! I was looking at “min unsupported wall thickness” when I should’ve looked at “Min unsupported wires” in the design guidelines for brass. Still it passes automatic checks, and the technicians don’t complain about it. So maybe I’ll keep it like that. If it breaks, then I learn something. The chariot is kind of an add-on for now, anyhow. It’s unfinished.
At what angle are your feed sprues, relative to the main sprue?
Most of that work was done by hand. It will depend much on part shape, how much you need to open it so they stack neatly. Anyting from 15 deg to 45deg most of the time, if you do an image search on google you will see the trend. You need 2mm diameter at least, more if they get long. Lest they break when the mold ceramic is poured over the patterns.