Yeah, I include a sprue as part of the item I am currently going to make.
And you are correct, a wax tree is the way to go but here is why…
Shapeways will charge 10 dollars just as a handling fee for each 3d printed wax item, then they just add a cost for the volume of wax. This is normally only 3 dollars.
But let’s say I want to make a marine/ship center stud link chain and I need like 40 wax models. I sure as hell can’t pay shapeways to print me 40 different small waxes. So you are right, if I make a wax tree of say, 20 of the anchor chain links all as one model, (must be within the 75mm X 50MM bounding box), then shapeways will only charge me 10 bucks plus the volume of the wax.
I think this is still cheaper than paying an old school mold making company, and I don’t have wax injectors anyways.
Here is a picture of the ring I’m going to cast. Sorry for the terrible photo, my office computer has a crappy graphics card so it can’t even render the shapeways preview of the model. But you get the picture of the sprue.