Within the last two years our company began making fixtures for use in our production environment.
Recently we discovered we were able to 3D print a part that we previously purchased consumable molds. This discovery has lead to incredible cost and time savings.
The issue we dealing with now is how to document this model. The finished part does not come out as an exact replica of the solid model which is where the concern is.
The dimensions in the solid model are the correct sizes in order to produce the correct sizes.
So the question is how do you document a part that will knowingly not match the solid model (which is ok and "intended") so that it can be sent through quality assurance and the next engineer will know what is going on?
Normally when you have problems in the fabrication process you make allowances for this in the drawing.
In your case, you probably have some sag from an unsupported section.
The problem is, each 3D printer will behave somewhat differently so you may also have to specify the printer and settings on your drawing so that inspection has a heads up on what is critical and what is not.
We model the desired shape, then use the scaling functions on the 3d printer to adjust the print to match the desired dimensions.
I believe that it is for shrinkage, but I suppose it could be used to accommodate calibration issues as well. We have a low end printer. It does not have shrinkage compensation that I know of, so the scaling is what allow us to print objects to the correct dimensions.
I know of at least one person that needed to put the right pinions on the belt drives on a Makerbot to get the machine to scale correctly.
If the scaling you are applying is some magic whole number within the ratio of the drive pinion, you may have this rare issue.
That is interesting to know, since ours is a Makerbot 2X. We have not been able to get accurate prints without scaling. We can somewhat infer the proper scaling, but it seems to depend on the shape of the print. If we want the part to be accurate to the model, we need to print with the inferred scaling factor, measure, then re-scale and print a second time. With this we can generally get +/- .010" [.25 mm] or better accuracy on larger prints.
We have an older Dimension SST 1200es that was recently updated to be able to run more materials and a couple Makerbots (the 2X, I believe). The Makerbots are finicky as all get out and take constant tweaking to get good parts. The Dimension is networked, all we do is make the STL file, call up the Dimension software, position the part, send it to the printer and then hit print on the printer and we get consistent and accurate prints every time.
The Makerbots will theoretically produce finer detail, but they rarely get used because it takes too much work to get good parts.
For your situation, assuming a better printer is out of the question , I would want to have the master CAD model represent the final, desired size. Perhaps maintain a duplicate set of files in the proper scale, or maintain the STL files at the proper scale. For each part, note on the drawing or in a model annotation the required scale factor for 3D printing.
Thanks for the input. Sorry for the delayed response as I got pulled off of this project for several days.
After reading your posts I talked with my manufacturing engineer and convinced him to make the Creo model accurate and adjust his settings on his printer.