Surface Roughness

From: wayne l foss (
Date: Tue May 05 1998 - 19:19:49 EEST

First of all, I would like to state that I understand the desire of
everyone to have very smooth part surfaces. So would I, BUT...


This had been brought up when I first set up our Stratasys facility and
some tried to make issue of it. The surface quality of FDM parts when
compared to SLAs is obviously not good. But when addressing this with my
internal customer, I ask them, is this the most important function of
the part that I am prototyping for them. Why is it important? What do
you really want to find out from this prototype at this stage of the
design cycle? In the vast majority of cases, it is only an appearance
issue that is a perceived problem. The surface roughness usually does
not play into the functionality of the prototype part. Yes, I know that
there may be fit issues and it becomes a problem when there is movement
between parts (which for us is rare). If the surface quality is an issue
with them, I advise them to make the part through traditional methods. I
usually get to build the part anyway.

I sometimes feel that there is too much emphasis placed upon getting a
perfect part just for show. Painting parts to a "production" finish, I
feel, is adding unneeded expense to the part just for "fluff". Our
design staff has impressed the pants off of our external customers at
design reviews with raw SLA, SLS and FDM parts. They are impressed with
the designs progress and our efforts to show them a product that they
can touch and sometimes operate early on in the design cycle. Our
customers are intelligent and have insight. However, there are times
when you need to display prototype products at shows and confrences that
need to have the production looking parts. The finishing time and costs
are justifiable in this instance, although I am expecting a customer to
someday order 10K of these products for delivery next week. Too good has
the potential to bite you later.

At this point in time, I am satisfied with the surfaces produced by the
current technologys and I think most of my customers are also. I have
faith that the system producers whill continue to address this issue and
will provide us with better looking parts in the future. I will
patiently wait for them to do this and will not spend a lot of effort to
research finishing methods. By the way, I ran across a product made by
Dupli-Color called Scratch Filler & Primer. It can be found in auto
parts stores. Works great on FDM parts.

- Wayne L. Foss                  
- Engineering Services                     Phone  319/295-2631
- Rapid Prototyping Specialist             FAX  319/295-5429
- MS 106-176
- Rockwell Collins, Inc.	 
- 400 Collins Road, NE             
- Cedar Rapids, IA  52498-3161
DISCLAIMER: Unless otherwise indicated, this correspondence is personal
opinion and NOT an official statement of Rockwell Collins, Inc.

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