Re: 3D printing challenges etc.


Ed Walters
 

Has anyone tried 123D from Autodesk for generating STL files? It seems to be targeted at the same market as sketchup, but given that it presumably includes some of Inventor's core, it might be less susceptible to the leak problems?

--- In STMFC@yahoogroups.com, "Rob Kirkham" wrote:

well, I can't disagree with you Dennis.

To answer the "other software" question, I use two programs - both free - to
convert and scale a Sketchup file. So first I export a sketchup file as a
3d model. Then I import the 3d model file into Meshlab, open it and export
it as an STL file. Then in Accutrans I open the STL file and scale it. I
know there are less clunky ways but I learned this in the early days of
Shapeways services, when Rene Gourley was the only one I knew who had tried
it. He put me onto these softwares - they were specifically recommended by
Shapeways. They work, so I haven't learned a better way - which I know
others on this list have done.

Rob

--------------------------------------------------
From: "soolinehistory"
Sent: Friday, February 08, 2013 7:46 PM
To:
Subject: [STMFC] Re: 3D printing challenges etc.



--- In STMFC@yahoogroups.com, "Rob Kirkham" wrote:

yes - but if using Sketchup to scale the drawing to HO, you can also run
into the 6 decimal place rounding problem if you are not careful.
Dividing
most large numbers by 87.1 seldom produces neat 6 (or fewer) digit
quotients. Using other software to scale a full size drawing allows one
to
get around that problem. But drawing with the rounding problem in mind
from the get-go is also worth some effort.

Rob Kirkham
I think Rob's problem lies elsewhere.

Let me preface this comment with the confession that I am by no means an
expert on Sketchup... In fact, I've never used the software, and all I
know I've learned from poking around in their help files and discussion
lists, looking for answers to Rob's questions.

That said, the problem lies not in what scale the object is drawn in, or
how many decimal places entered points are calculated to. If one were to
draw the gusseted end of a hat section brace as a portion of an ellipse,
or a NURBS curve, extrude that profile to give it some thickness, lay it
over modeled sheathing with V groove edges, and preform the Boolean union
operation to attempt to make them one solid, the software is going to
preform all kinds of calculations to the limit of its precision, no matter
if the original data was entered to three place precision, two place
precision, or limited to whole numbers.

The problem is that while software operating with solids as the native
environment will either do the operation, or choke right then and there.
Sketchup, on the other hand, will happily trim all the surfaces and
display them, without any indication that the different surfaces that
define what you assume to be a solid do not have concurrent boundaries,
and you won't learn that until thousands of operations later, when you try
to convert the file to STL format. You end up with something that Sketchup
calls "leaky solids", which is basically the software development team's
admission that their product can't reliably calculate boundaries with all
points within the internal margin of error for concurrent points. It is
basically the difference between freeware, and software that will set you
back multiple thousands of dollars.



Dennis



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