Altering STL files in Rhino

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pyronaught
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Altering STL files in Rhino

Post by pyronaught » Fri Apr 17, 2015 5:30 pm

Can someone explain the procedure for modifying models in Rhino when all you have is the STL file to work with? If I import an STL file, it comes in as a mesh and I can't seem to convert it to anything else that would allow modifying the model. There's a MeshtoNURBS command, but it has a size limit on it and the part I want to change exceeds that limit.

The part I'm trying to modify is the M2 Extruder Motor Mount, which currently allows the motor to spin if the screws get loose (and since there are no lock washers on these, they get loose over time). If the extruder nozzle drags over some ooze or other defect that didn't lay down perfectly flat on the previous layer and the clamp bolts have worked loose, the motor assembly rotates and changes the nozzle position and the print is ruined at that point. This has happened to me several times already. The motor mount could be modified to utilize the flat side of the motor as a brace to prevent it from spinning and also insure the extruder is aligned perfectly vertical during assembly. I've noticed the v6 hot end nozzle is more prone to collecting goo during a print, and this problem is amplified if the extruder assembly is not aligned perfectly vertical. So two problems to solve here with one simple modification to the motor mount.
Experience is what you get when you didn't get what you wanted.

jsc
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Re: Altering STL files in Rhino

Post by jsc » Fri Apr 17, 2015 6:30 pm

You cannot. If your imported part is a mechanical thing (like a motor mount), you can use the mesh as a guide for redrawing the part.

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Jules
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Re: Altering STL files in Rhino

Post by Jules » Fri Apr 17, 2015 8:04 pm

Wait, wait! I know this one......I've modified a few from Thingie..... :)

The current version of Rhino does have some limited ability to work with meshes, but it's sometimes tedious. Everything has to be performed in the Mesh Tools tab section, and there are a bunch of pretty squirrelly limitations.

For instance, If you need to extend a face on an existing mesh file, use the Mesh Creation tools to make a mesh block, then use the Mesh Boolean Union tools to combine them. To retract a face, use the block of mesh to subtract from the existing face.

You also need to attach/draw the block with all the Vertex, Point and End snaps turned on - if the edges/faces don't align EXACTLY the Boolean Union fails. (I like to pre-place extra Points to tie to if needed.)

And sometimes it is much quicker to just re-create the original file, so that is always an option.

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jimc
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Re: Altering STL files in Rhino

Post by jimc » Fri Apr 17, 2015 9:05 pm

yup, its pretty much just as jules said. dont bother converting a mesh to nurbs, even if it allows you to. it just comes out a big mess. you need to work with the part as a mesh. open up that mesh tab and have fun..lol

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pyronaught
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Re: Altering STL files in Rhino

Post by pyronaught » Sat Apr 18, 2015 3:37 am

I saw a Rhino plugin which claimed to convert meshes to solids but all the reviews said it fails miserably. I notice some people include the original model file in IGES or similar popular formats on thinigverse, but not very often.

I notice the Osnap tools don't work on meshes either. That's going to make finding the center point of holes a big pain when using the mesh as a guide to rebuild the model. That center snap mode is one thing I use a lot when building models.

Are the M2 parts available in anything other than the stl format?
Experience is what you get when you didn't get what you wanted.

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jimc
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Re: Altering STL files in Rhino

Post by jimc » Sat Apr 18, 2015 4:13 am

iges, step, and sldprt convert well into rhino as a nurbs model. working with meshes is horrible and a pia. some people include the original model on thingiverse and some dont. in most cases i have found it better to just model it myself anyway. even if you found the best converter from mesh to nurbs that you could find it would never give you a real clean model like it was created originally in rhino.

jsc
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Re: Altering STL files in Rhino

Post by jsc » Sat Apr 18, 2015 9:10 am

While looking at that nextengine scanner that came up a little while ago, I saw that they had some interesting software that converts scanned meshes into fully parametric CAD models: http://www.nextengine.com/products/rapidworks/intro

Price is a bit high for me, though.

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PcS
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Re: Altering STL files in Rhino

Post by PcS » Sat Apr 18, 2015 2:57 pm

Here is the stock rhino motor mount file in .3dm. I hope this is ok ? If not please delete.
Attachments
extruder mount.zip
(848.46 KiB) Downloaded 372 times

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pyronaught
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Re: Altering STL files in Rhino

Post by pyronaught » Sat Apr 18, 2015 3:48 pm

I'm using Rhino 4.0 and it is not able to open that .3dm file because it was created in a newer version of rhino.
Experience is what you get when you didn't get what you wanted.

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jimc
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Re: Altering STL files in Rhino

Post by jimc » Sat Apr 18, 2015 3:54 pm

Oh man time to update!

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