Re: I Wish...

From: Rob Connelly (Becton Dickinson  & Company)
To: RP-ML
Date: Friday, January 20, 1995
Subject: Re: I Wish...
Dave Flynn and I were saying...
>>(1) I would hope that ALL of the RP vendors and users out there would start looking ...

>If the laser power, Ec, and Dp are known accurately (and are truly ... What are your thoughts?
     Those were my thoughts as well.  The whole thing is summed up by "print through".  
We are working on a quick and dirty solution here by pulling up all of the facets 
in an STL file that exhibit any negative value for the z component of the normal 
vector.  It is only a band-aid, however, since there are secondary effects caused 
by slice's interpretation of the NEW geometry.  A fix implemented at the slice 
level would be more accurate, and using a fixed compensation value (like the 
present beamcomp) would be a good first crack, and would reduce the error by an 
order of magnitude without introducing a lot of rocket science.

>BTW, we've observed that up-facing to up-facing vertical dimensions are ... What have you seen?
     I concur here as well.  I have run z-shrink test parts that show from 0-.015% 
shrink every time; 3D's calibrations don't seem to be able to mess this one up.  
We do, however, use the small value that we calculate.  And yes, I'm measuring +/- 
LT for up-facing to up-facing also.  As a matter of fact, when you plot error vs. 
measurement, you can actually see the discrete LT steps!

Rob Connelly