ATTN: Zhien RE: Matching between positive and negative part of a 3D mold

From: Monica & Glenn Whiteside (SiderWhite@worldnet.att.net)
Date: Tue Aug 25 1998 - 04:20:08 EEST


Zhien, you wrote:

Hi there,
I am working on gelcasting of ceramic nozzle. In order to easily remove the
mold from gelcast part, we designed the 3D mold (built by SLA-250 using
epoxy resin) into two half. So, we need registration pins on each half
mold. However, after biulding, the pin (positive) did not match with the
hole (negative). Generally, the pin has larger dimension than the hole (in
CAD file, we draw the pin and hole diameter using same dimension). Does
anyone know what is the basic procedure to make the pin (positive) matching
well with the hole (positive) for a 3D mold. We tried to adjust the shrink
compensation for both pin and hole in Maestro. However, it did not work. Do
we have to correct the error in CAD file? That is, to draw the pin smaller
than the hole.

I appreciate any help and suggestion.

Thank you again for your attention.

Zhien Liu
Research Associate
Dept. of Mater. Sci. & Eng.
Case Western Reserve University
Cleveland, OH 44106

Zhien:

I've always had better luck modifying the CAD file - usually the best way is
to oversize the hole by say .002" for a 1/4 dia. hole to compensate for
shrinkage. Leave the male pin net - usually it is easier to sand the pin to
fit if necessary - although you can easily ream the hole out, it is real
easy to take too much material out of the hole this way.

Another way is to make the female hole oversized and pot knurled bushings
into the SLA part and use steel pins - this is a lot more durable for
tooling - we've successfully used this technique for making sheetmetal
formblocks with SLA models.

Good Luck,

Glenn Whiteside
e-mail: siderwhite@worldnet.att.net

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