RE: [rp-ml] FW: Geometric Accuracy of RP parts

From: David K. Leigh <>
Date: Wed Dec 29 2004 - 17:49:01 EET

I just thought I'd weigh in on the cost effective methods for RP inspection.
Free-form inspection is very difficult and costly. Many times, the energy
and effort to put a complex geometry on a CMM or similar and inspect it
outweigh what it took to actually build the part. So. . . What to do? I
think it boils down to 2 things - design and cheaper inspection methods.

Design - There is design for manufacturing. There can be design for
inspection as well. Stay away from cool ergonomic shapes and break complex
parts into individual part assemblies. This isn't always possible - but
have you ever seen some of the amazing mechanical systems they built before
there was a calculator?

Cheaper Inspection - An example of this is the diameter of a hole. You can
use a rod to check the diameter very quickly. Templates and overlays can be
used to see if holes line up. There are many manufacturing techniques such
as jigs that are very simple in nature that are very cost effective. A pdf
file and a good printer give you a really cheap and accurate way to make a

There are tons of ways to skin this cat. I think as techies we many times
make problems more complex than they really are. Sometimes we create that
"bigger and better" mousetrap that costs a ton - but is it more effective?
Not always.

David K. Leigh (254)933-1000
Harvest Technologies fax(254)298-0125
Rapid Prototyping Services

-----Original Message-----
From: Rose & Crangle, Ltd. []
Sent: Wednesday, December 29, 2004 8:15 AM
To: 'Anshuman Razdan'; 'Good, Jim';
Cc: 'Marshall Burns';;
Subject: RE: [rp-ml] FW: Geometric Accuracy of RP parts

Many rp methods use lasers to bond or cut. Is it correct that every
laser beam has some reflectivity, however small? If so, is it possible
to detect that bounce-back on a real-time basis? If so, can that be
used as feedback to detect not only the bonding/cutting position of the
beam in four dimensions, but also the heat at the target spot? If so,
can software be programmed such that if variances from design exceed
certain pre-set or dynamically reset values, the laser beam can be
immediately fine-tuned in power as well as in x-y "aim" without halting
the laser bonding or cutting?

Bob Crangle

-----Original Message-----
From: [] On
Behalf Of Anshuman Razdan
Sent: Tuesday, December 28, 2004 11:45 PM
To: Good, Jim;
Cc: Marshall Burns;;
Subject: RE: [rp-ml] FW: Geometric Accuracy of RP parts

Either the inspection system must measure as the part is being built or
once its built you cannot measure the internal structure with surface
scanning methods. Then MicroCT must be employed, which has its own
issues ...


-----Original Message-----
From: [] On
Behalf Of Good, Jim
Sent: Tuesday, December 28, 2004 7:15 AM
To:; Anshuman Razdan
Cc: Good, Jim; Marshall Burns;;
Subject: RE: [rp-ml] FW: Geometric Accuracy of RP parts

The inspection system must provide the required data to determine if the
part is geometrically acceptable for its intended purpose.
Additionally, we
would want real-time inspection to verify the part-build, as each layer
produced. Is this feasible? Can we make it work? Is it over-kill?
are things we will explore. Maybe we only need a post-build inspection.
Either way, this part must be verified before the astronaut, or robot,
attempts to replace the part within a system.

Ernst, I agree with your comments.


Muniz Engineering Inc.
In Situ Fabrication and Repair (ISFR)

-----Original Message-----
From: []
Sent: Tuesday, December 28, 2004 6:00 AM
To: Anshuman Razdan
Cc: Good, Jim; Marshall Burns;;
Subject: RE: [rp-ml] FW: Geometric Accuracy of RP parts

Hello RP's,

The RP system has to have a reasonable cost of ownership to be
If the build process of a RP system has to be based on a built in
to receive accurate, reliable and consistent parts, this RP system has
chance on the market.

The problem comes if the part is removed from the RP system, has to fit
into the existing assembly and perform the needed functionality. Then a
measuring system can define the deviations between the build versus the
designed form or define the modifications needed to perform the needed
For simple parts, a CMM is a good solution. If the part is complex, with
free forms, warped or bended, a scanner is usually preferred to
the problem (3D color plot with selected deviation flags) and get it

Then depending on the selected measuring technique, the specific
preparations have to be done to get data fast and in good quality (e.g.
built a fixturing for the part on a CMM or dull shiny or transparent
for scanning).

I do not fully agree with the statement: "it depends on the tolerance",
depends much more on the part, the available time and the application.

We wish you a happy new year, with best regards

Ernst Müller
GOM International AG
Bremgarterstr. 89b Tel. ++41 56 631 04 04
CH - 8967 Widen, Switzerland Fax:++41 56 631 04 07

             Anshuman Razdan


             Sent by:
             owner-rp-ml@rapid Marshall Burns

    <>, "Good,

                                       Jim" <>,


             28.12.2004 05:48

                                       RE: [rp-ml] FW: Geometric
                                       of RP parts

It depends on the tolerance. Laser is good, but requires dull surfaces
best results. Any sharp angles or shiny metal will throw it off. There
other metrology techniques but they are not fast. Speed vs accuracy is
age old problem.


      -----Original Message-----
      From: []
      Behalf Of Marshall Burns
      Sent: Monday, December 27, 2004 7:57 PM
      To: 'Good, Jim';
      Subject: RE: [rp-ml] FW: Geometric Accuracy of RP parts


          This is a very important idea you're looking into. I don't
      specific recommendations of scanners for you, but just thought I'd
      chime in about the concept. Even in a terrestrial application,
      this kind of thing that will provide the feedback to ensure that a
      fabber is on track, and let it make mid-course corrections. It's
      obviously that much more critical in a remote application, like

          I'd be interested to learn more about your project as it

      Best regards,
      Marshall Burns

      -----Original Message-----
      From: []
      Behalf Of Good, Jim
      Sent: Monday, December 20, 2004 13:45
      Subject: [rp-ml] FW: Geometric Accuracy of RP parts
      I thought I would throw this out. I am looking into inspection
      equipment that will verify the geometric accuracy of my RP part,
      after fabrication, and actually during fabrication. I've looked
      laser scanning and got some good input already. I'd like
      opinion on what system they are using and what they believe to be
      best system to verify geometric accuracy. The ultimate goal is to
      build a fabricator that contains an integral inspection station.
      This system would be used in space for repair and fabrication of
      parts. Any thoughts?


      Jim Good

      Muniz Engineering Inc.
      In Situ Fabrication and Repair (ISFR)
Received on Wed Dec 29 16:30:23 2004

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