Re: Improved Accuracy Tools

From: Bert VandenBerg (
Date: Thu Apr 22 1999 - 17:02:53 EEST wrote:

> Are there any "automatic" and easy ways to compensate and make a new STL
> file when you have got your first 3-D file and the first cast tool, which
> will because of metal shrinkage be smaller than your first 3D model?
> What programs and services are available to make this second 3D model
> easily? The model has to be exactly as much oversized as the shrinkage of
> the first tool?

Commercial tools that I know of are limited to applying (global) scale
factors, or a
(global) surface offset to the CAD model.

While at NRC (, we developed a method for automating the
model correction process. The process was:

0 make an initial part-RP model-tool
1 create a FEM model of the part
2 scan the part (laser scanner or other fast digitizing method)
3 - fit the scan data to a STL model of the part
   - calculate the deformations required to distort/shrink the features of
       the FEM model to match the scan data
   - invert the deformations calculated to predict a model shape that would
       produces a part with the required shape
4 produce an improved part-RP model-tool

Step 4 was automated by a program running on a workstation.

The good news is:
- the method improves the accuracy of parts produced
- it independent of the part shape, material, or manufacturing process
- its quite automatic

The less good news:
- step 4 typically takes hours to run (for the implementation developed).

For more information on this technology, contact Dr. Jeff Xi (

Bert van den Berg                   E-mail:
Hymarc Ltd.                 
35 Antares Drive                        Tel: (613) 727-1584
Ottawa, Ontario  K2E 8B1                Fax: (613) 727-0441

For more information about the rp-ml, see

This archive was generated by hypermail 2.1.2 : Tue Jun 05 2001 - 22:51:31 EEST