Successfully building parts w/ trapped volumes

From: Holger Wirtz (
Date: Fri Jun 07 1996 - 21:23:05 EEST

Hello Prototypers,

I changed by subscription to this list a while ago to receive the digest, but
never got even one ... this is why I am back to normal subscription. Maybe the
list"master" could try and figure out what the problem is? Thanks.

About the subject: I'm not sure if someone has already come up with this (since
I've been off the list for quite a while as mentioned above), but I'll post it
anyways cause I think it has some significance. I've built parts with trapped
volumes easily with the following trick:

I am creating a part that is somewhat similar to the trapped volume (i.e. sthg.
like an offset of the walls of the trapped volume, e.g. with a support software
like Magics by turning around the part, creating a solid support and flipping
back again), positioning it inside the trapped volume and I am building this
part together with the original, except that I am building the dummy part with
a hatch spacing of about 5 mm. This way, the trapped volume is divided into a
lot of smaller trapped volumes, but wiping the material off of those smaller
volumes is not a problem at all. I have succesfully built lots of parts that
way; the only disadvantages are that cleaning up is somewhat more work, more
material is used and building the part takes a little bit longer than usually.

I have not experimented with larger hatch spacings yet, but I'm sure larger
hatch spacings are tolerable, depending on the viscosity of the resin. I am not
sure how SLAs handle hatch spacings of 5 mm, we are using a STEREOS 600 here
which allows separate values for hatch spacing, scan velocity and laser power.

Comments are welcome. Happy building.


---------------------------------------------------------------------- "Opinions expressed are solely my own and thus do not represent or are in line with those of my employer ..." Dipl.-Ing. Holger Wirtz email: Research engineer at the Fraunhofer Institute of Production Technology Steinbachstr. 17, 52074 Aachen, F.R.G. phone: +49 (0)241 8904-120

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