Re: Some reliable equations for RT

Date: Wed Feb 06 2002 - 18:23:27 EET


Bill's last paragraph is very truthful. In all RP methods, you will find
that the people who produce the best products have a firm knowledge and
understanding of the equipment, materials, and the design/ engineering
process. In stereolithography this is particularly important. Building SL
parts is easy and can be taught rather quickly. Building good quality,
accurate parts that will give your client the end result they are looking
for requires knowledge and experience, which does not come quickly. This
means that you must have somebody who is able to tweak a resin and a
machine to give the best possible results. This includes, knowing how a
machine and its parts operates, how materials work, and what all of those
"mystery" values mean. You must then build the parts on equipment and
resin that is well dialed in to produce good parts. All of the parts must
then be post processed by skilled people. Keep in mind that all of this
must be done usually under tight time constraints, and within budget.

There are many variables that go in to producing good parts, none of which
are achievable without knowing how the entire process works. A person
working in RP must be part engineer, designer, chemist, craftsman,
technician and witch doctor.

David Yarnell
Dynacept Corporation
845.278.8530 P
845.278.8501 F

                    "Bill Richards"
                    <brich@deltasearc To: "mepstein" <>, <>
          > cc:
                    Sent by: Subject: Re: Some reliable equations for RT
                    02/06/02 08:54 AM

Hi, Molly,

Interesting question! The answer will be just as interesting and will take
many people to answer it correctly. It will also depend in what context you
want this question answered.

Look at a cheetah, the fastest animal on Earth. It expends an enormous
amount of energy in order to catch just one meal. As a result of this
expenditure a cheetah can starve to death even if it is hunting on a
basis, if it is hunting animals it has to chase down over long distances.
in spite of their speed, a cheetah will frequently ignore prey it could
potentially chase down or even give up a chase if it goes too far.

Humans are no different. But when we find a task that is too difficult, we
build tools to enhance our ability to get the job done. Want to have a
better spear to hunt with? Put a stone arrowhead on it. Stone isn't good
enough? melt metal and make a metal arrowhead. Need to dig through rock to
make more arrowheads? Make a tool that will cut through the rock better.
Want to go to the moon? Build a rocket.

A rapid prototyping machine is simply a tool that helps us improve the
development of products. But rapid prototyping does not begin and end with
machine that generates physical objects -- it is a process. To make any
process work well, you need someone who understands that process from
beginning to end to manage the workflow. This person will need to have an
understanding of a wide range of skills in order to coordinate what needs
be done.

A business functions the same way as does any animal. In order to survive
and thrive, the business needs to perform its function with the least
of expenditure. Often enough, we do replace people with machines, and costs
go down, the business survives. But there are certain skills that cannot be
replaced by a machine. It is not the hammer that builds the house, it is
carpenter that wields the hammer that builds the house.

Too often, a rapid prototyping machine is looked upon as a labor replacer.
"Get a prototyper, and you won't need as many people in the tool room!"
Nothing is further from the truth. What the RP machine does is enhance the
development of new products and technologies, but it requires someone to
work that tool properly. If anything, it may require one or more workers in
the tool room to be retrained to know other skills to make it work right.
But if definitely won't replace those people. And the better they know how
the machine and the process works, the better they will work that process.

Businesses do have a tendency to try consider the position of "rapid
prototyping technician" as an unskilled labor, and try to hire people whose
skills are not up to the true task. Ask any RP service bureau what they
think, and I am willing to bet that their answer will be quite the
Someone most successful with managing the RP process will understand not
just how the RP machine works, but be familiar with the issues of 3D
and then the post processes such as molding and casting.

That requires skill and experience. It also helps to know how things work.


Bill Richards
Delta Search Labs
T: 617-551-4615
F: 617-551-4651

----- Original Message -----
From: "mepstein" <>
To: "Lamar Davidge" <>; <>
Sent: Tuesday, February 05, 2002 9:12 PM
Subject: RE: Some reliable equations for RT

> Hello,
> I am new to this list and I wanted to introduce myself. My name is Molly
> Epstein, I am art student and am very interested in rapid prototyping
> processes. I don't know if this list gets philosophical or if it just
> technical, but it seems pretty informal and welcoming. This post from
> Davidge made me think of a lot of things that I believe to be a really
> problem in my experience with people. My school is the only college that
> know and it is what I am responding to, so bare with me but I really feel
> the next generation of students coming out of great art schools really do
> know the fundamental requirements of making things work well, and using
> and machines correctly, not just making mistakes but really not
> the way things work. It seems that we are rushed and pushed away from
> learning how things work, or how to do something with the best
> and quality. How do any of you feel about this? Have any of you seen a
> digression in quality and craftsmanship throughout your time doing what
> are doing?
> -Molly
> Will,
> >
> > You forgot to mention that tool life is also affected by the ability
> >the employees who are responsible for running the tool. I have seen some
> >very simple tools ruined on the first shot due to mistakes, a 150 ton
> >closing on an aluminum or epoxy tool can wreak havoc, not to mention
> >injecting at 2500psi, instead of 350 psi, can do to a fragile tool. Also
> >epoxy is very strong, but if you drop it on the floor with the core side
> >down it wont last long. The best constructed tool, with the best
> >design, wont last long if you dont have people who are skilled running
> >
> >Lamar Davidge
> >-------Original Message-------
> >
> >From: Pattison, Will
> >Date: Friday, February 01, 2002 06:35:11 PM
> >To:
> >Subject: RE: Some reliable equations for RT
> >
> >in my experience, the only equation that can be used to determine shot
> >in a rapid tool is something like:
> >
> >tool life is inversely proportional to part complexity, inversely
> >proportional to how many parts you need, inversely proportional to how
> >your customer is willing to spend, inversely proportional to how fast
> >need parts, directly correlated to the material they want, and directly
> >proportional to the real toolmaking knowledge that goes into design of
> >rapid tool.
> >
> >i'd be curious to see any mathematical model that effectively takes all
> >into account.
> >
> >will pattison, skeptic
> >product development
> >ignition
> >plano, texas
> >
> >
> >-----Original Message-----
> >From: Chang-Shik Min []
> >Sent: Friday, February 01, 2002 9:23 AM
> >To:
> >Subject: Some reliable equations for RT
> >
> >
> >
> >Dear Rapid Tooling specialists:
> >
> > are you today ? I have survived this field of RT research
> >1994.
> >Based on statistics,probability and stochastics,I have been trying my
> >to simplify all the RT business processes,especially for quoting and
> >
> >control.
> >Meanwhile,I have recently come up with some highly reliable empirical
> >equations for tool (which is made by RT methods)life estimation,part
> >estimation for low-mid volume production from RT molds.
> >Is there any one who has ever tried to make some empirical equations for
> >?
> >Any comment you could give me would be greatly appreciated.
> >TIA
> >
> >
> >
> >
> >
> >
> >_________________________________________________________________
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