Sprueing is a method of joining a multi-part model into one. The benefit of this is that most 3D Printers charge an additional flat rate per “part” even if it is in the same model. Separated parts usually can add as little as $1.50 to even a $6 charge per part.
Sprueing does have its own challenges as different materials require different thicknesses. Most white strong materials require at minimum 1mm thickness. 1mm sprues are rather springy and “give” when pushed or dropped. Resin (Sculpteo) requires a 2mm thickness. Each material has its own requirements for sizes so it is always best to keep this in mind when printing. When I first did this I was concerned that it was adding costs and “waste” to my model, however with Shapeways recent price changes it actually reduced the cost over all. (Shapeways.com before October 7th 2014 it would have raised the price!)
At home printing is slightly different as instead of printing the whole thing you might print on a flattened plain or each individual piece separately. Sprues and Cages are really only for commercial grade printers that use the powder layering process.
Pictured above is version 1.0 hands of one my models I am working on. It consists of 2 joints on each of the 4 main fingers, 2 thumbs, 2 5mm pegs to fill the wrists if needed and 2 palms. Totaling 20 parts. Without sprueing this model would cost over $30. By placing sprues in the model this costs less than $10 depending on the material selected.
The above is printed in white strong polished. It has a rather nice “spring” to it when pushed on but bounces back rather well.
Spruing is a rather easy process basically I personally use Tinkercad. Adding in columns and sizing their thickness to 1mm then placing them so they connect and create a strong structure. Most smaller pieces only need one connection point. (Fingers, and joints…) And on the larger parts I have 2-3 connections.
If your model is not going to be polished then you may not need as many sprues. However… If you plan for it to be put through several processes its best to add more.
While sprues do add a little more labor involved after receiving the model in the end it does provide the printer you use a LOT less work involved. (Somewhat wish they would speed up the ordering process on models like these!)
These sprues if done small enough to spec they really do not even leave a mark once cut. I use the following tools to remove and scrap excess away.
Wire cutters or Scissors. (To cut each part from the rest of the model initially.)
Elmers/X-Acto X3037 Axent Knife with Cap, Blue. (To clean the parts of any excess.)
Use your wire cutters to cut away at the sprues freeing up each piece. It is ok to leave some room on the parts. As the final process you will use your X-Acto Knife to scrap layer by layer to smooth the spots where the sprues joined your parts.
In following this process and using the above tools I was able to remove any excess material from the sprues. I was afraid that it might leave marks or bumps on the model but it actually did not. You do have to be slow and careful and take small layers at a time off till you get a smooth surface. Smaller parts are easy to mess up on so be careful and go slow. White Strong Plastic can be pretty forgiving depending on the model you print.