Tech Question About CAD and RP

[indieFan]

I have a question for those of you that have experience with CAD and RP (particularly multi-jet modeling):

If you built a model of something and wanted to make a stand for that model, taking into account the fact that the material shrink is not uniform through, would you still base your stand on the original drawings or would you measure the actual model that has been built to create your stand? (Note that the stand is not made from an RP.)

My hunch is that without a uniform shrink factor, one would have to measure the actual model to create a stand to any degree of accuracy. However, there are a great number of tricks in the world of engineering, and I'm hoping that someone out there would be able to give me one for this particular issue.

Thanks,
indieFan

[Elgin Clock]

I would use the model in CAD as a starting point. Then make a model of the stand (I'm assuming a display stand?) from the dimensions in CAD. Then, if your rapid prototype machine alows for it, upload both model and stand (if it fits in the bed of the machine) and make them both at the same time.
edit: My reasoning behind this, is depending how intricate the thing is you want displayed, if you print both the stand and the model at the same time, you will more than likely have the same percentage of "shrink" effect on both of them. No worrying about the shrinking of the stand after you measured the part to an exact measurement and it not fitting.

It would help to know what kind of Rapid Prototyping machine you were using.

The one I have experience with is a "cheap" line from Z-Corp and it uses glucose and starch to make the model. Depending on how big you want your model and display stand, you can "print" them both at the same time, just leave space between the two, so it doesn't adhere them together when making them in the RP machine.

Hope that helps..

[indieFan]

You are correct in thinking that I will be building a display stand. The model is made out of wax on a 3D Systems ThermoJet printer, but the display stand will be made out of plastic by someone in the campus machine shop.

The model that is being created had to be done in a piece-wise fashion, as the size of the overall model was too large for the ThermoJet to print as one single piece. Doing the model part by part also made support removal on certain pieces much easier. As a result of the individual parts being printed at different times and in different configurations, there is no way that the parts would have uniform shrink. (Previous measurements of multiple parts built on the same platen also showed that the shrink was not uniform even within that single build.)

indieFan