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Author Topic: Struggling with a 3D profile, Chapter 2.  (Read 572 times)
jgmick
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« on: May 12, 2018, 01:02:14 am »

I started a new thread because the original had kind of walked off topic (which was MY fault. Apologies. I know better than that).

A comment from "Bubba" caught my eye during the discussion so I went back to re-visit that.

Bubba: "Yeah, the solid is of very poor quality. You can't expect good finished part from it.

First, help me understand if what I see is that issue with the quality. 
When I look at the STL file in CamBam and explode it I see the "regions" (in another life those were called facets.) I  understand how the 3D solids are actually built, so no surprise there.  If I select a region in the list, CamBam will highlight it.  That let me walk down thru the list identifying several of them. 
Question: Is what I am seeing in CamBam the actual representation?  If so, I agree that it is pretty poor.  Few big flat regions, in particular I noticed that there are not many segments around the XY plane arc.

Follow-on question: How far down (how many more and smaller regions) do you expect to see before it moves from "poor" to "good"?  What is a metric to judge that on?  Eyeball, region span along the curve (technically probably measurable as a chord error from a true arc thru the midpoint of the region.), other?  I actually extracted a bit of that info from the CamBam generated .NC file by looking at the ends of the tool path segments that are the outer bound of the cavity.  A little tedious but I had noticed that the end of the tool path that followed that XY curve was a series of short but straight lines (G1 codes) where I would have expected arcs. (G2 or G3) with a radius that matched the overall curve.  Didn't do enough points to actually form a judgment but probably could.

Final note:  I started experimenting inside TurboCAD to see if I could make it better.  So far no luck but there is much there I also have to learn.  (Help files kind of run out of info when you try to drill down far enough.  Common problem to all kinds of S/W.) 

Last question: (Desperation may be creeping in.) If TurboCAD can't export finer grained models, is   there anything out there in a post-processor that can "clean up" or "polish" a 3D solid?  Would a .3DS
export be any better?  I think not, but asking anyway.

Comments welcome. 

P.S This has been a very good place to learn things.  Thank you again for your able assistance.
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dh42
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« Reply #1 on: May 12, 2018, 02:15:17 am »

Hello

Quote
Question: Is what I am seeing in CamBam the actual representation?

Yes, the surface object will be machined "as is", so facets will by visible on the final part with the same size that on the 3D model.

I do no know TurboCad, the file I attach was done with SolidWorks, and the resolution can be set when the soft convert "mathematical object" to mesh object ; it's a setting in the export page. (rough, fine, custom)



the stl used here is saved as "fine" in SW
http://www.cambam.co.uk/forum/index.php?topic=7355.msg59351#msg59351
Quote
A little tedious but I had noticed that the end of the tool path that followed that XY curve was a series of short but straight lines (G1 codes) where I would have expected arcs. (G2 or G3) with a radius that matched the overall curve.  Didn't do enough points to actually form a judgment but probably could.

3D toolpath can use arcs, but only on XY plane, so they appear only when using the waterline methods ; because the STL as no "true" curve, CB use the same function used for polyline to replace small line by arcs (arc fit) to fit arcs in toolpath.

on Waterline MOP, set Auto Arc Fitting to true, and use non zero value for Arc Fit Tolerance

if you read some French, I've done a more detailed document about how works 3D machining operations .. but not yet translated in English sorry . (and not totally finished)

http://www.atelier-des-fougeres.fr/Cambam/Aide_V1/tutorials/Usinage3D_overview.html

++
David
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Bubba
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« Reply #2 on: May 12, 2018, 02:27:44 am »

A comment from "Bubba" caught my eye during the discussion so I went back to re-visit that.
*************************
Honestly, I don't know enough about solids creation to be able give advice. What I do know that is pretty much 'what you see is what you get' kind of deal. And it look like the solid have some faceds inverted and is really rough witch would create problems if you were using 1/16" ballmill. In your case .25 dia cutter in relation to the size of your model shouldn't  affect the finish much at all. I hope that this explanation make sense to you. Good Luck.
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jgmick
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« Reply #3 on: May 12, 2018, 14:33:04 pm »

Thank both of you for the feedback.  I found some commentary in the CAD help file about setting and adjusting the mesh size (that term I am familiar with) and also some words about "smoothness". I'm going to fool around with those and see if I can improve things.

Bubba: Just knowing that "WYSIWYG" is real is a big help.  Thanks.  That will let me see if I'm doing any good in my mesh experiments.  I have the NC file from the work you folks did, so I think I may just throw a piece of stock in the mill and run it and see what I get.  That will tell me just how much more fighting I need to do.  Run time looks to be about 2 hours, maybe a little less. (I don't much care as long as it's under a day.)  Aluminum bar stock is cheap, so why not try it?
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Bob La Londe
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« Reply #4 on: May 14, 2018, 02:19:50 am »

Well, what you see is sort of what you get.  In the MOP settings resolution is a possible issue as well.  

Let me back track.  I use ViaCAd primarily for my 3D modeling.  I have Fusion as well, but I am just more accustomed to ViaCAD.  When I export an STL file I get a pop up screen with a bunch of settings.  The only one I ever change is Normal Deviation.  By default it is set at 8.  That creates fairly coarsely faceted STL files.  For 99% of my work when I drop that number to 3 its "good enough," But for some things I'll drop it to 2 or sometimes, but rarely, 1.  The smaller that number the smaller the triangle facets.  

I would note that the the finer the resolution of the STL the larger the file size.  CamBam can be pretty good, but it does have some file size limitations.  Multiple STLs can also cause memory issues.  

Now as to the other matter.  When doing 3D cuts the resolution is what determines how often CamBam checks for proper depth along the tool path.  Its a % factor of tool size.  .05 means a distances equal to 5% of tool diameter.  

~~~~

Just out of curiosity I tried normal deviation just now on a sphere from .1 to 20.0.  I received results from .5 to 16.  Lower resolution than 16 gave the same as 16.  Higher resolution than .5 crashed.  
« Last Edit: May 14, 2018, 02:25:57 am by Bob La Londe » Logged

Getting started on CNC?  In or passing through my area?
If I have the time I'll be glad to show you a little in my shop. 

Some Stuff I Make with CamBam
http://www.CNCMOLDS.com
jgmick
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« Reply #5 on: May 18, 2018, 12:13:07 pm »

Progress!  Found a setting in the CAD program for "smoothness".  Unscaled, range 1 to 99.  Default when I entered was 50.  Cranked it up to 99, got about a 5:1 increase in STL file size.  STL files are pretty much linear with facet count, so that looked good.  Imported into CamBam, much better visual appearance.  Side note:  When I saved the .cb file it went from 50K to 1Meg.  Definitely making CamBam work harder.

I drew in the bounding polyline along the lines of the file that Bubba had posted.  Now how do I create that subordinate region to include all of the facets in that bounded area so I can feed it to a 3D profile?

Question to Bubba: This is part of my continuing education on CamBam. Why did you add in that small radius in the lower left corner of the bounding polyline as opposed to just running the X and Y lines down to a point?
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