Re: 3D printing challenges etc.


Dennis Storzek
 

--- 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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