3D tool-pathing; Roughing vs Finishing

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RaspberryJamGuitars
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3D tool-pathing; Roughing vs Finishing

Post by RaspberryJamGuitars »

Hi,

Can anyone please explain why the 3D "finishing toolpath" has exactly the same estimate of how long the machining time is regardless of the prior 3D roughing toolpath? I am guessing the 3D finishing toolpath just does the smoothest job it can and "assumes" you will take care of the roughing process. It seems odd they are not interdependent. By which I mean, if I ran a more fine-grained roughing tool path, the finishing toolpath should be quicker than that required after a very broad two pass roughing path. But it is not.
So if I am right, you have to "manually" select a roughing toolpath that will not break the mill ends used in your smoothing toolpath. Am I right? Any advice of hacks on what to do to ensure this does not happen?
I look at comments on this forum and also my own practice and a 12.7 mm roughing toolpath in some cases, will do two passes on a quite deep 3d model, ie the roughing toolpath is so broad brush as to be useless. You can make it more useful by changing the depth of cut of the 12.7 miil bit, it a few more contours appear but as noted the finish toolpath does not recalculate to reflect these changes.
I am thinking that if the toolpaths, as I suspect, do not "talk" to each other, why would I not do an aggressive feedrate 12.7 mill roughing pass, another quite aggressive 6 mm mill roughing toolpath, to get the roughing done in a reasonable amount of time, leaving the finishing toolpath to be undertaken a bit quicker than otherwise as the pass depth would be will within the limits of the finishing mill end.
Am I going crazy, am I right, what is lurghi? Help please.

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Re: 3D tool-pathing; Roughing vs Finishing

Post by adze_cnc »

I think that you are over-thinking things. From the documentation: "Finish Machining is used to machine the final pass on the finished 3D part."

That is that the cutter contacts the model over the entire course of it's finishing toolpath (dependent upon tool stepover). Therefore whatever material that may or may not have been removed by any roughing toolpath can't affect the time needed for the 3D Finishing toolpath. The only variables that can affect finishing toolpath time are speed of travel and stepover of the finishing tool.

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Re: 3D tool-pathing; Roughing vs Finishing

Post by Rcnewcomb »

I am thinking that if the toolpaths, as I suspect, do not "talk" to each other
The roughing and finishing toolpath have no knowledge of each other.

The finishing toolpath ALWAYS cuts at full depth.

A roughing toolpath is only needed:
  • to avoid breaking your finishing tool because there is too much material to remove
  • to provide clearance for your finishing toolpath to reach (a half inch long tool carving 0.75 inches below the top surface)
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Re: 3D tool-pathing; Roughing vs Finishing

Post by litzluth »

I would add to Randall's list that adding a roughing toolpath widens your options on machining strategies in a way that can solve problems that would otherwise exist (e.g., eliminating distortion and other problems caused by tool flex or other defects caused by a particular strategy, that don't exist with a finish toolpath calling for only a small amount of material removal)

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Re: 3D tool-pathing; Roughing vs Finishing

Post by Xxray »

The finish pass doesn't care if its been roughed or not.

I use roughing on an as needed basis, and it is needed when hogging out large amounts of material in hard wood and/or plexiglas.

Soft woods, shallow cuts you might well get by without the need to rough, totally your choice - And yes, you do take a chance that you overstress something and something will give [either the tool, material or hold down] if you chose not to rough.
For that matter, you can snap a roughing tool just as well if you use it too aggressively.

One trick you can try to minimize risk of breakage is to calculate the finish at a 45 degree angle, this way the tool starts out with a very small corner area and works its way up diagonally instead of a full length shrieking pass [the 1st pass is the one to worry about as 100% of the tool is in contact with the material].
After the 1st pass, only half the tool is in contact, greatly minimizing stress/friction/heat/noise ect.

Proper feed rates and RPM are also critical for not over stressing bits.
Doug

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Re: 3D tool-pathing; Roughing vs Finishing

Post by RaspberryJamGuitars »

Thanks to all!! I feel a bit of a goose as I did not mean to post this topic, having indeed determined I had overthought stuff and the finish toolpath must necessarily cut to full depth. However, the discussion it engendered was very helpful.

I have now experimented with two roughing Toolpaths which at quite aggressive speeds and feeds, can be quicker than one more conservative toolpath. This then allows a more rapid finishing toolpath as well. I think I can sometimes save a bit of machining time with this new found perspective so happy days.

Thanks to the responders and stay safe.

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Re: 3D tool-pathing; Roughing vs Finishing

Post by TReischl »

RaspberryJamGuitars wrote:
Mon Dec 28, 2020 12:55 am
.....
I have now experimented with two roughing Toolpaths which at quite aggressive speeds and feeds, can be quicker than one more conservative toolpath. This then allows a more rapid finishing toolpath as well. I think I can sometimes save a bit of machining time with this new found perspective so happy days.

Thanks to the responders and stay safe.
Really? How so? Hint: It could be that you are still over thinking this topic.
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Re: 3D tool-pathing; Roughing vs Finishing

Post by Clockman »

Yes,
I would also like to know how you do two roughing toolpaths.?

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Re: 3D tool-pathing; Roughing vs Finishing

Post by adze_cnc »

I’m not sure that you’ve provided enough information in the question. Creating multiple toolpaths is trivial just keep clicking on the roughing toolpath icon. You could create a dozen if you really want to.

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Re: 3D tool-pathing; Roughing vs Finishing

Post by Tailmaker »

One more reason to do a roughing pass: If the finish bit flute length is too short for the required material removal depth.

But in many cases, it is not required to do a roughing pass for the entire model area. I often make only a narrow roughing start slot (with an appropriate boundary vector) to prevent the finish bit cut full depth at full diameter doing the very first row. After that, with small stepover, the bit may well be capable to keep going.

Even with a roughing pass you may still break a finish bit if your model has deep holes or pits that the bigger roughing bit cannot reach.
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Re: 3D tool-pathing; Roughing vs Finishing

Post by Xxray »

Creating them yes, but actually using them and the reason to do so is the question.
Raspberry seemed to think you can be faster and more aggressive using two, so I suppose if you really wanted to you could simply set your Z a bit high, do one, then set the correct Z and do the other, which would of course be the same actual toolpath.

Why ? I'm stumped, unless maybe you have a machine built out of plastic and foil. If I'm worried about overly aggressive cuts, and yes I have been, I'll do a 45, which eliminates the stress of the 1st cut with no downsides that I can think of [And yes, I realize this thread is a couple years old] Never too late to hash these things out !
Doug

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Re: 3D tool-pathing; Roughing vs Finishing

Post by Leo »

The way the roughing and finishing toolpaths are set up gives you the most options as to how you want the 3D carving to be done.

Maybe you may want ONLY a finishing toolpath with no roughing. If the carving is shallow and the material easy to cut and the tool is robust you may not need roughing.

Maybe you can get away with only a roughing toolpath and don't care about a finishing pass.

I have a customer that does not want to change cutters. He wants only one cutter for roughing and finishing. I created a program for him using a 1/2 ball mill to do 3D roughing agressively - then 3D finishing to get a good finish - then a 2D cutout - ALL in one program using the one cutter - 1/2" ball mill.

It's all up to you HOW you want your machining strategy to work.

It is a good thing that the 3D roughing and the 3D finishing toolpaths are completely independant of each other. It allows for many options.
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Re: 3D tool-pathing; Roughing vs Finishing

Post by Leo »

oops - I didn't realize this was 3 years old.
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