Cut2d rounding corners

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Cut2d rounding corners

Postby JNOV » Fri Jan 19, 2018 4:17 pm

I've seen a number of posts about rounded corners, with many replies suggesting that the problem is the constant velocity setting in Mach3. My problem is different; I see the rounded corners within Cut2d. I checked the "sharp external corners" option in the profile dialog, but it doesn't seem to make a difference.

I've attached a screen shot so you can see what I'm talking about. Note that at each point where the profile path has a sharp, roughly square corner, the toolpath cuts straight across. The result (which is plain in the 3D preview which I didn't attach to save space) is that what I'd like to be sharp corners are replaced by unwanted flats. There's no problem with clearance; the tool is small enough to make the cut. I don't know if the problem is that I'm trying to cut "external" corners on an inside profile (so that perhaps the "sharp external corners" option has no effect).

I'd really appreciate any help, suggestions, or insights.

Thanks!
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cut2d corner shave.jpg
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Re: Cut2d rounding corners

Postby Adrian » Fri Jan 19, 2018 4:26 pm

That's an inside cut so you're not going to get sharp corners as it's a physical impossibility with a round bit. External corners generate a different cutting strategy.

The sharp corners option only really applies when using a v-bit as that can lift to create sharp corners.
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Re: Cut2d rounding corners

Postby LittleGreyMan » Fri Jan 19, 2018 4:35 pm

In your 3D preview, doesn't the cut match the internal profile?

Could you post the same 2D preview with the "Solid" option activated?
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Re: Cut2d rounding corners

Postby JNOV » Fri Jan 19, 2018 8:09 pm

Thank you very much for your replies, gents.

Adrian -- Thank you, but I don't understand why the sharp corners in my profile can't be cut correctly with a round bit. What's the difference between cutting those and cutting around the outside of a square profile? Even though it's an inside cut, it seems like the corners should be cut as external corners (i.e., because the angle of the corner cuts is about 270 degrees). If instead I'd attempted an outside cut of the same profile, I'd expect to have the issue you suggest, because then the cutter would be on the "inside" of the corners (i.e., because the angle of the corner cuts would be about 90 degrees) and following the profile with a round bit would be physically impossible.

LGM -- the 3D preview shows that the sharp corners are removed and turned into flats. When I get home, I'll attach screen grabs of the 3D preview and the 2D preview with the solid option selected.

Thanks again!
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Re: Cut2d rounding corners

Postby JNOV » Fri Jan 19, 2018 9:02 pm

Adrian -- Just to follow up (and I don't mean to be argumentative, as you obviously know more about this than I do), imagine taking one of the corners in my profile, removing it from the rest of the profile, and turning it into a closed triangle by adding a third side. Now, if I told Cut2d to cut an outside profile around that triangle, it'd have no trouble producing a toolpath that would yield the correct triangle, with its sharp, non-rounded corners. Notice that 2/3 of that hypothetical toolpath (i.e., the portion that includes the two original legs and the corner they define) is precisely the same toolpath that I want for the 12 sharp corners of my inside profile. I think that the only difference between the hypothetical and my actual scenario is that in my case, Cut2d is using its "inside" profile algorithm, while in the hypothetical case it's using its "outside" profile algorithm. It's clear (I think) that I can manually (e.g., in my CAD software) construct an "on" profile that will yield the toolpath I want by offsetting (on the inside) from the original profile by half the cutter diameter and dealing with the corners using the same strategy Cut2d uses to create toolpaths for external corners in outside profiles (there are actually myriad ways to do this, particularly since I don't care what happens to the material inside the profile), but it seems like there should be some way to make Cut2d calculate such a toolpath automatically.

Am I missing something?

Thanks again.
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Re: Cut2d rounding corners

Postby Adrian » Fri Jan 19, 2018 9:43 pm

Could you attach the file? I've tried the same pattern and bit combination right down to a 2mm sized piece and I don't get the same toolpath you're seeing. I initially posted when I was on my phone and it looked like a normal toolpath to me. Now I'm home on the large screen I can see what you mean.
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triangle.JPG
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Re: Cut2d rounding corners

Postby JNOV » Fri Jan 19, 2018 10:09 pm

Thanks, Adrian. I'll attach the file when I get home.
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Re: Cut2d rounding corners

Postby JNOV » Sat Jan 20, 2018 2:37 am

Hi Guys -- I've attached two files related to my profile: a close-up of a portion of the 2D solid preview. You can see that the corners get clipped. I've also attached the underlying Cut2D file so you can take a look for yourselves.

I've also attached a solid preview of a toolpath generated for a simple L shape, which like my profile has an internal/external corner. Cut2D handles this corner as I'd expect, so I'm thinking it could be an issue with my particular profile.

Any thoughts appreciated.

Thanks so much!
Attachments
cut2d corner shade solid preview.jpg
half servo spline.crv
(66 KiB) Downloaded 35 times
cut2d L solid preview.jpg
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Re: Cut2d rounding corners

Postby Rcnewcomb » Sat Jan 20, 2018 7:15 am

I found two things
1. The vector has an irregularity. The Vector Validator tool shows an intersection at about the 7 o'clock position, but it was a bit difficult to fix. I switched the project over to metric and then it showed up as an open vector. Then I was able to use the join vector command.
Intersection.PNG

Attached is a corrected vector in EPS format
half servo spline.eps
(2.86 KiB) Downloaded 92 times


2. The other thing was that the pass depth is only 0.1mm, so it is taking 24 passes to cut through the material. Perhaps that is correct, but it seems like you could get by with a 0.3mm pass depth on a 0.6mm bit.
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Re: Cut2d rounding corners

Postby Adrian » Sat Jan 20, 2018 8:59 am

This is very odd. It will only generate the strange toolpath if the tool is 0.6mm in diameter. Make it 0.5mm or 0.7mm and it generates the correct toolpath. I drew a new shape to rule out any vector issues.

I can't see any reason why it should behave like that so this might be one of those that needs to be directly reported to Vectric to get an answer unless anyone else has a bright idea.
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Test Angle.crv
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Re: Cut2d rounding corners

Postby JNOV » Sat Jan 20, 2018 4:27 pm

RCN -- Thanks so much for figuring out that there was an irregularity with the vector. I'm a newb and didn't even know the validator tool existed! I used join open vectors to create the vector, and it never occurred to me that when the close open vector operation reported 1 closed vector and 0 open vectors that there might be a problem. Unfortunately, the problem persists even with the corrected vector. (By the way, I hadn't yet run my feeds and speeds calculator to figure out the optimal depth; 0.1mm was just a conservative placeholder. This is a very small cut that needs to be done very precisely, so I'm going to try to keep deflection to a minimum and figure that I may end up with a very shallow cut depth.)

Adrian -- Thanks for investigating! I changed the cutter diameter and get the same results as you. Very odd. Unfortunately, my end mill actually is 0.6mm, not 0.5mm or 0.7mm!

The strange thing is that I was unable to produce your results with other shapes with similar properties. For example, I created a bunch of vectors by taking various size "pie" slices out of a circle and never saw this behavior when specifying a 0.6mm cutter. So I started to think that maybe the problem is caused by the interplay between the particular angle in my original profile and 0.6mm. I investigated that idea a bit, and I think it may be right. I took my original vector and created a new shape with the same corner angle (which I think is what you did, by the looks of the graphic you attached). As expected, I saw the same issue when specifying a 0.6mm cutter and an inside profile. Then I copied that new vector and used the node editing tool to change the angle very slightly. Voila -- no more problem, as you can see in the attached screen capture.
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cut2d corner comparison.jpg
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Re: Cut2d rounding corners

Postby Adrian » Sat Jan 20, 2018 4:46 pm

If the angle is the same as your original one it's pure coincidence as I drew that shape from scratch. I suspect it's a tolerance/rounding issue in the software with the interaction of vector size/angle/bit size.
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Re: Cut2d rounding corners

Postby JNOV » Sat Jan 20, 2018 5:22 pm

Interesting -- thanks again for all your help
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Re: Cut2d rounding corners

Postby LittleGreyMan » Sat Jan 20, 2018 5:29 pm

Adrian wrote:If the angle is the same as your original one it's pure coincidence as I drew that shape from scratch. I suspect it's a tolerance/rounding issue in the software with the interaction of vector size/angle/bit size.


And it may probably occur with other values combinations. JNOV, better send your file to Vectric support so they can investigate this bug.
Best regards

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Re: Cut2d rounding corners

Postby JNOV » Sat Jan 20, 2018 10:10 pm

Thanks, LGM. I sent an e-mail to Vectric support. I'll reply to this thread with any news.
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