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  #21  
Old 02-10-2018, 09:36 PM
Jim_in_PA Jim_in_PA is offline
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And that, ladies and gentlemen, is how you get the smoothest cut for that moon on your outhouse door...

(And more seriously, that particular thing around closing vectors, etc., was exactly what I was struggling with the other night on some play drawing I was doing...)
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  #22  
Old 02-10-2018, 11:21 PM
Mike Fuson Mike Fuson is offline
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Quote:
Originally Posted by BradyWatson View Post
Mike,
See attached pic showing a shape created with 4 nodes and 4 arc spans and the same shape comprised of many nodes and straight spans. While the one comprised of a bunch of nodes and straight spans may not appear any worse than the one comprised of 4 arcs in wood, there may be a reduction in cut quality if you were cutting plastics or aluminum parts, that would show up as small facets on the edges of the part.

The nodes and spans directly influence the toolpath trajectory and high node count shapes often are jagged when you zoom in. Many times this is from artwork from the customer, but VCP and Aspire will also generate low quality vectors when you use the 'lazy tools' - like bitmap to vector or relief boundary tool. I always either rebuild these by tweaking nodes or just manually digitize boundaries using the polyline tool, and then node editing. Less nodes with arc, bezier or lines drawn correctly will yield superior results in every way compared to the lazy tools...Low quality vectors may work fine for some applications, but sooner or later they bite you...garbage in, garbage out.

So 'clean' means making the vectors as smooth and regular as possible. This sometimes means cutting out sections of the shape and replacing with a single arc, bezier or line in order to give a nice clean path for the tool to follow. This is 2nd nature to me having done it for so long.

In terms of 'closed', this means that the vector shape, unless it is to be used as a single centerlining toolpath (Vectric speak = Profile toolpath, ON) - needs to be continuous with no gaps or loops that cross over like a shoelace loop. Quite often in creating complex shapes, you lop off a part with the scissors/trim tool and the part that is left is now an open vector. This must be closed, using the join/close tools before you go to machine it.

For example, you may have a rectangle where you remove the top span. Now it is open. If you take the polyline tool and click on the top left node and top right node to close it with a span, it is still open...as is the polyline span you just created for the lid. You ALSO need to join both of them together using the join tools...now this is a simple example. You could have also used the join/close tools and selected the option to close the open rectangle with a straight span & it would be closed and ready to cut.

The software has a few tools that are very helpful in checking yourself. If you go up to Edit-Select->Open Vectors, it will look for open vectors and select them for you so you can close them if need be. Many times clipart and even stuff from customers will come in with duplicate vectors on the same layer. You go to edit one and it looks like you didn't do anything because there is another one right below it. This is where Edit-Select-Duplicate Vectors is really helpful to flush all but one set of vectors on that layer.

Only after making sure your vectors are clean and closed should you proceed to toolpathing. Quite often, if your vectors are not up to par, the toolpathing engine will pop up a message and tell you there are open vectors or vectors not suitable for machining. If you discipline yourself with your drawing style, you can avoid a lot of problems later on in the pipeline.

Does this make sense?

-B
3 weeks ago it wouldn't have made sense, but now it does. thanks for taking the time to explain, especially the function of the tools.
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  #23  
Old 02-11-2018, 08:38 AM
BradyWatson BradyWatson is offline
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Mike,
You're welcome.

Most people cannot appreciate what goes into CNC work. There is some thought pattern that gives the impression that CNC work is just 'pushing a button'. Only by learning the process can one have a real appreciation for this work.

Be hungry, be unstoppable and try your own ideas along the way. Expect to fail a lot...but that's never without merit. You always get something out of it. Before you know it, you'll be in the gifted class!

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