topic Re: Arc center is not correct in Machining Discussions Forum

Arc center is not correct

Lonnie.Cady — Thu, 05 May 2016 16:46:03 GMT

Has anyone experienced any issues with the arc center not being correct in milling?

I have a 180 deg semi circle and its center is located at x0 y0 but the the tool paths in SW is off and the posted code show the y center being off .0043"

I drive the tool path off the edge of the model and it is off. I created a sketch circle that is concentric to the model and if I cut a full cirlce the toolpath and code are correct?

In the below I have duplicated the operation and selected both so both toolpaths are displayed. One is drive off model edge and the other off sketch. You can see in the first image they overlap. As you approach the top they no longer line up. I can't share the file publicy. I shared it with @jeff.walters.

Was more curious if anyone else was seeing this. I found it by cutting 2 parts and putting them together and they were correct across the split but off .009" the other direction and scrapped the first sets.

Re: Arc center is not correct

Lonnie.Cady — Fri, 06 May 2016 11:37:15 GMT

Well I can't figure it out so you may want to beware that arcs can be out of positon. Probaby won't matter in most situations but does not give any real confidence when cutting them.

Re: Arc center is not correct

Rob_Lockwood — Fri, 06 May 2016 14:43:03 GMT

I haven't come across this, but since you can't share the file its pretty much a dead end for me. Hopefully Jeff/Dev comes up with something?

Re: Arc center is not correct

Lonnie.Cady — Fri, 06 May 2016 14:47:15 GMT

@Rob_Lockwood what email address do you want me to use. I just don't want to post it publicly. Probably not a big deal as it is just a simple part. I shared with laurens also.

Re: Arc center is not correct

Laurens-3DTechDraw — Fri, 06 May 2016 15:11:03 GMT

And I couldn't find anything wrong with what Lonnie did but see the issue. So something weird is really happening.

Re: Arc center is not correct

Lonnie.Cady — Sat, 07 May 2016 10:40:11 GMT

Thanks for looking @Laurens-3DTechDraw It was only off .005" not a big deal. Obvioulsy not too concenrning since it has been a month or two since reported.

Re: Arc center is not correct

Lonnie.Cady — Fri, 20 May 2016 23:41:04 GMT

HSMWorks 2016 R3.40915 still not working.

Re: Arc center is not correct

Laurens-3DTechDraw — Sat, 21 May 2016 04:48:46 GMT

No support wants to take a look at this?

Re: Arc center is not correct

Lonnie.Cady — Sun, 22 May 2016 12:41:01 GMT

Nope now one. Not big deal as I just just had it cut the full circle to get it right. It obviously cut a lot of air but got thru them. I just reprogrammed in SmartCAM for this repeat order I have to make.

Re: Arc center is not correct

Laurens-3DTechDraw — Sun, 22 May 2016 14:21:02 GMT

Let's try @dave.anderson @jeff.walters @al.whatmough @mircea.rohat @fonsecr @mikkel.ostergaard @griffew @matthew.nichols , anyone of you got an idea what happens here?

This seems pretty serious to me, I should be able to trust the system to cut the correct selection. If I can't the whole system is useless.

So an explanation ASAP would be much appreciated.

Re: Arc center is not correct

fonsecr — Sun, 22 May 2016 21:27:31 GMT

Hi all,

I'll have a look at the example from Lonnie the coming week and will let you know what I find out.

René

Re: Arc center is not correct

Rob_Lockwood — Sun, 22 May 2016 21:32:41 GMT

And here we see the elusive Fonseca in his former habitat...

Re: Arc center is not correct

Lonnie.Cady — Sun, 22 May 2016 23:00:43 GMT

Thanks @Laurens-3DTechDraw for getting this looked at.

Re: Arc center is not correct

fonsecr — Mon, 23 May 2016 15:45:10 GMT

Hi Lonnie,

I looked at your issue now. The problem has to do with our internal smoothing which just looks at the tolerance when making sure toolpath is ok. The arc center can be moved around a lot within a given tolerance.

In this case you can set Minimum Cutting Radius to 0 which will force smoothing to be off which again ensures the desired arc center.

Another parameter that can change arcs would be Compensation Radius Allowance (for lead ins/outs). But in this case that is not the issue.

I can look into why the smoothing in this case moves the center but in general this is permitted. But you can work around this problem but setting the Minimum Cutting Radius. Smoothing is generally desired to remove redundant points in the toolpath but it will change the toolpath slightly.

René

Re: Arc center is not correct

Lonnie.Cady — Mon, 23 May 2016 16:05:10 GMT

If the tolerance is set to .0004" how could the toolpath pass as okay if it is off .0041" or a factor of 10x the tolerance.

Re: Arc center is not correct

fonsecr — Mon, 23 May 2016 16:37:16 GMT

The arc center is not directly important when checking that the toolpath is ok. You can move the center a lot before it causes arc curve to fall out of tolerance. So you cannot assume that the center will move only within the given tolerance from the ideal arc center.

René

Re: Arc center is not correct

Lonnie.Cady — Mon, 23 May 2016 17:30:03 GMT

I understand that, but in this case it causes the entire toolpath to be off by the distance it is below center. I cut 2 of the pieces in the file. I put them together to create a single ring the measurement across the split vs 90 deg to the split was off .0085" or about .0045" per part. So regardless of where the arc center ended up the toolpath does not stay with in tolerance.

So if you completely remove the arc center from the equation the the toolpath is still incorrect. At the top of the y axis the toolpath is off regardless of the arc center position by 10x the tolerance.

It is obviously over my head on this, but how can I be sure things like arcs like this are in the proper true position? I did not have smoothing turned on and the tolerance was set to an acceptable level for this part. How could one deduce that the min cutting radius would effect the internal smoothing and there by shift the toolpath .0041"

In the attached screen captures I tried to stop at x 0 as close as I could for both toolpaths. If you do the math between the 2 toolpaths the y axis is off .00414". Is that the toolpath that is being check against the tolerance? If so it is off by 10x. If not what toolpath is beign checked against the tolerance I set for the part.

Re: Arc center is not correct

Laurens-3DTechDraw — Mon, 23 May 2016 17:29:28 GMT

@fonsecr wrote:
The arc center is not directly important when checking that the toolpath is ok. You can move the center a lot before it causes arc curve to fall out of tolerance. So you cannot assume that the center will move only within the given tolerance from the ideal arc center.

René

In this case the toolpath is out of tolerance by 10 times.

Since the toolpath is 0.004 off the arc center and since the path is 180 degrees the "fault" of the path is 10 times bigger than the tolerance.

As I understand some smoothing will have to occur in the system, this is way more then I would ever expect it to.

Re: Arc center is not correct

fonsecr — Mon, 23 May 2016 18:41:42 GMT

I am going to check why it happens but it will take some time. I'll post once I have it analyzed.

René

Re: Arc center is not correct

fonsecr — Tue, 24 May 2016 11:25:17 GMT

I analyzed it now and located the problem. I created ticket CAM-4191 for the team to look at.

René