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Excel Gurus?
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Author:  npalen [ Sat Mar 24, 2012 9:07 pm ]
Post subject:  Excel Gurus?
I would like to try reverse engineering some of my archtop plate profiles in Rhino.
I have the digitized point clouds in Excel which, with necessary header info, is what I use for machining the plates.
These are parallel tool paths with stepover with X running parallel with the centerline of the plate.
The main longitudinal arch would be easy to derive as it is the X coordinates along Y0.
The transverse arches would, however, be a bit tedious to extract and could use some help.
Is there a way to tell Excel to extract all the Y coordinates that form an "arch" at a given X coordinate?
P.S. I assume that Rhino has a curve offset function that would allow for the stylus/ball mill radius? I use the the same radius ball mill that I use for digitizing so they normally cancel each other.
Thanks
Nelson
Author:  ballbanjos [ Sun Mar 25, 2012 6:44 am ]
Post subject:  Re: Excel Gurus?
I wonder if the "pointcloudsection" command might give you what you're looking for. Here's a link to a description of the command and how to use it:

http://www.rhino3d.com/5/help/commands/pointcloudsection.htm

You'd have to import the pointcloud data into Rhino as an .stl file or something like that first, but it might be easier than trying to do it all out of Excel...

Dave
Author:  Don Williams [ Sun Mar 25, 2012 7:52 am ]
Post subject:  Re: Excel Gurus?
Nelson, if you have all the data points, you can use a pivot table to extract all the data you're looking for.
Don
Author:  npalen [ Sun Mar 25, 2012 9:32 am ]
Post subject:  Re: Excel Gurus?
Dave, that's awesome and works great!
I'm sure some of you other Rhino guys are aware of that also.
Don, can you explain the "pivot table". That sounds interesting.
Thanks, guys.
Nelson
Author:  npalen [ Sun Mar 25, 2012 11:47 am ]
Post subject:  Re: Excel Gurus?
Don, I did a search on "Pivot Table" in Excel and found the info.
Didn't know there was such a thing so will need to investigate further.
Thanks
Nelson
Author:  Parser [ Thu Apr 12, 2012 11:14 am ]
Post subject:  Re: Excel Gurus?
Hi Nelson,

I think what you really need is to model your parts, based on the point clouds you have digitized(?).

If you haven't seen it already, here's a quick link showing how to compensate for the probe tip diameter:
http://www.emicroscribe.com/uploads/fil ... sation.pdf

If your current point cloud already represents the actual surface of the part, then you can use Analyze>Surface>Point Set Deviation to see a nice color coded plot showing where your surface deviates from the point cloud and by how much.

I hope this helps - the real challenge is doing the surfacing!

Trev
Author:  npalen [ Thu Apr 12, 2012 11:10 pm ]
Post subject:  Re: Excel Gurus?
Trev,
It sounds like a trial and error process to zero in on the best match of the developed surface to the point cloud.
You do this by tweaking the curves one or two at a time and then checking the resulting surface?
Author:  Parser [ Fri Apr 13, 2012 3:51 pm ]
Post subject:  Re: Excel Gurus?
Yep, that's the process. You get your framework setup and then begin the process of massaging the framework to get the surfaces to match the point cloud. This is something that is usually a little quicker to do in a parametric modeling app like SolidWorks, versus a tool like Rhino (at least until you get to the point where SW starts bogging down!).

There are two things that you have to keep in mind while doing all this:
1) the part that you digitized was probably not perfect
2) the digitizing process is probably not perfect.

You also have to ask yourself how critical it is that you match this surface exactly on a part that will ultimately be scraped, sanded, etc...!

Trev
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