After some interesting carving problems I finally figured out the difference between the Contour and Arc Post Processors (PP). I was having pockets that ended up having corners with different radii. It initially seemed like a random occurrence but I finally tracked it down to having selected the Contour PP on one machine while designing and the ARC PP on the machine connected to the shark - I do design while the Shark is running a job. The Aspire preview showed all corners looking identical and correct but when running I would end up with three larger radius corners (significantly larger than bit radius).
So far what I have found is that the major difference between the two processors is the precision. The contour PP has the command "G64 P.1" which tells the control box to maintain the machine surface (or edge) within .1 inches of the actual g-code command. The result is that the .125 radius corner that I expected from my .25 inch end mill became a .225 inch radius corner. This occurs for three of the four pocket corners. The one good corner is where the toolpath moves to an larger path.
The ARC PP has the command "G64 P.01" which means it holds the profile within .01 inches of the desired profile. The calculated machining times are the same in ASPIRE in both cases since Aspire is PP agnostic. When loaded into the control panel the original Contour PP file had a shorter machining time than the ARC PP file. Presumably this is because it can go faster around the corners of the pocket. The machining time with the modified Contour with precision set the same as the original ARC PP had the same machining time when loaded into the control panel.
A lot of you probably knew this already but now I get to my questions:
What PP do you use?
Do you use the same one for V-carve and 3-D carving?
Do you stay with the precision as provided by Nextwave or have you changed it? If so what do you find the best value.
Tom
PS this explained to me why I used to get what seemed like wildly varying machining times (2 to 3X) for some 3-D carvings. I probably have interchanged the two PP's because the default has been different on my two computers for some time.
Post Processor and precision
Moderators: al wolford, sbk, Bob, Kayvon
Re: Post Processor and precision
The Shark Owner's Manual provides information on the difference in post processors provided - along with editing instructions as well. The CNC Shark Post Processor pdf has the same discussion. Both are available for download from NWA's Downloads page. I suspect they are on the installation disk with newer purchases as well - but I don't know that for sure.
I have found great success using the Contour when using a 3D carving toolpath. Otherwise, I use the Arc pp. Every now and then I'll use a custom pp where I've set the G64 to 0.00 - I want it exact and no influence in error from the behavior of the control software. When I use 0.00 I generally lower the FRO down a bit more as there are some trades in other aspects of the outcome. If you're running a profile toolpath on a square for example, and running it at 120 ipm, when it is set to 0.00 it is going to go all the way to the next vertex before it even thinks about changing directions. Depending on the material, you may see some poor outcomes due to other aspects of the Shark - like flex - or router TIR, etc. Another instance where 0.00 wouldn't be useful is an oval - but it has several vertices along the vector - not arcs. With 0.00 you would 'see' each of these points in the edge of the cut.
Another use case for 0.00 is drilling - or mortising for hinges - particularly if you have a need for an exact outcome.
In general though - the default parameters found in the 2 pp's are what I've used in my projects.
The time estimate in VCarve/Aspire is just a guess that you'll want to tweak to give you a more accurate outcome. I built a little table for the different toolpaths and Shark pp's based on the times estimated when the tap file is loaded on the Control Box. That way when I'm sitting in front of Aspire I can tweak the time estimate parameters and have a better 'match' to the actual run time on the Shark setup I have.
I have found great success using the Contour when using a 3D carving toolpath. Otherwise, I use the Arc pp. Every now and then I'll use a custom pp where I've set the G64 to 0.00 - I want it exact and no influence in error from the behavior of the control software. When I use 0.00 I generally lower the FRO down a bit more as there are some trades in other aspects of the outcome. If you're running a profile toolpath on a square for example, and running it at 120 ipm, when it is set to 0.00 it is going to go all the way to the next vertex before it even thinks about changing directions. Depending on the material, you may see some poor outcomes due to other aspects of the Shark - like flex - or router TIR, etc. Another instance where 0.00 wouldn't be useful is an oval - but it has several vertices along the vector - not arcs. With 0.00 you would 'see' each of these points in the edge of the cut.
Another use case for 0.00 is drilling - or mortising for hinges - particularly if you have a need for an exact outcome.
In general though - the default parameters found in the 2 pp's are what I've used in my projects.
The time estimate in VCarve/Aspire is just a guess that you'll want to tweak to give you a more accurate outcome. I built a little table for the different toolpaths and Shark pp's based on the times estimated when the tap file is loaded on the Control Box. That way when I'm sitting in front of Aspire I can tweak the time estimate parameters and have a better 'match' to the actual run time on the Shark setup I have.
Re: Post Processor and precision
That is a grea tip, thank you.
With some of my projects it does not matter. But sometimes I am trying to cut slots in plastic that are only .010" - .030" wide, and sometimes those slots are circular. Oh, the humanity!
With some of my projects it does not matter. But sometimes I am trying to cut slots in plastic that are only .010" - .030" wide, and sometimes those slots are circular. Oh, the humanity!