Infinitesimal breaks in Arc conversions, halting CNC cutting

[lux_wales]

Hello,

I am having issues when converting curves to arcs for .dfx export. There appears to be minute lateral breaks in some of the converted arcs;

When I try to grip control points nothing happens, or dimensions return values in the order of 0.0000000

The outputted parts are to be water jet cut. The operator repeatedly sends my files back saying there is breaks in the geometry that require repair.

I can find no other information on this topic.

Any help on this would be greatly appreciated.

Thanks
Dan

[Helvetosaur]

Can you post an example (Rhino+DXF)? What settings are you using for dxf export?
–Mitch

[Willem (Willem Derks)]

Hi Dan,

Just to be sure, are the curves joined to begin with?
Are you converting in Rhino first and than exporting?
If so, are the conversions joined or separate curves?

[lux_wales]

Hi Mitch,

The area in question is highlighted here;

The curve was converted as a whole, I have exploded it to show the break.

Attached rhino file;2013-07-02 Floor Component for forum.3dm

I am happy with the export settings, the error seems to be in the original conversion to arcs

Snip of DFX export settings;

The process I have used is;
Unrollsrf
Duplicate edge
Rebuild curve (Small tolerance to reduce points, approx 0.1 - 0.4mm
Convert (options set as arcs)
Export as DXF

Thanks
Dan

[lux_wales]

Hi Willem,

Yes the curves are joined to begin with, I then convert to Arcs. Export to DXF
(I have exploded the converted arc conversion in the above file in order to highlight the error)

Thanks
Dan

[Helvetosaur]

Well, I do have a couple of questions concerning your file/procedure:

• Why do you need a file tolerance of .00001mm (one hundredth of a
  micron) on objects that approach 3 meters in length?
• But, if you run Join on your DXF curves they join into one curve. So
  the ends are within file tolerance of each other. even at that
  extremely small tolerance. Therefore there are officially no “minute
  lateral breaks” in the curves
• I do not see the gap you indicated in the first image. How far in
  are you zoomed? Can you actually measure that gap? It appears not.
• I also don’t understand why you need .07 degree angle tolerance when
  converting to DXF that’s also really tiny. Fortunately, you used
  Convert before, so the curves are already arcs, so that tolerance
  does not get used.

For me, the curves themselves look OK.
–Mitch

[heath]

Yep, looks fine here. My laser guy would have no issues with that curve. Well within tolerance. Might be an issue with the way his software reads your files.

[lux_wales]

Mitch,
Thanks for your reply, and your time on this.

“Well, I do have a couple of questions concerning your file/procedure:

• Why do you need a file tolerance of .00001mm (one hundredth of a micron) on objects that approach 3 meters in length? My mistake, in a desperate attempt to try and measure these distances, I altered the tolerance. No I would never normally use this tolerance.

• But, if you run Join on your DXF curves they join into one curve. So the ends are within file tolerance of each other. even at that extremely small tolerance. Therefore there are officially no “minute lateral breaks” in the curves. Yes my thoughts, whatever program I open the dfx in, the objects are joined.

• I do not see the gap you indicated in the first image. How far in are you zoomed? Can you actually measure that gap? It appears not. Zoomed in maximum and Agree.

• I also don’t understand why you need .07 degree angle tolerance when converting to DXF that’s also really tiny. Fortunately, you used Convert before, so the curves are already arcs, so that tolerance does not get used. Understood, I tried all sorts of DXF settings before finding the ‘convert command’.

Ultimately, this is the response I’m looking for; ‘They’re fine’
The company I’m using uses FlowPATH software, he has sent me back this screen shot, explaining the red squares are breaks / overlaps in the geometry, and could I fix them.

and these;

Having browsed the internet looking for answers I found this university tutorial for flowPATH and Rhino. File;FlowPATHtutorial.pdf

Screen shot of the ‘PURGE’ stage in the tutorial

I am wondering if he is aware of this function, or would this fix it? I suppose these are separate questions for another place.
Thank you again, this is a real help to know it may not be my end of things.
Dan

[lux_wales]

Thanks Heath, good to hear, wish he was my laser guy.

[jim]

Hi Dan,

It doesn’t sound like the purge command fixes this problem in Flowpath. That function seems to be for finding and eliminating duplicate segments.

Can Flowpath accept splines? I think the Rhino Convert command does not produce accurate enough arcs for Flowpath… Joining the arcs into ploycurves in Rhino does not fix the tiny gaps where the arcs don’t connect.

It looks like all the areas that Flowpath is having trouble with are areas where the curve should be straight. You probably don’t even want arcs in those areas. The arc on the end of your curve has
a radius bigger than the radius of the earth.

If Flowpath can take splines or polylines you may be better off making your curves in that form.

-jim

[heath]

@jim

I think the Rhino Convert command does not produce accurate enough arcs for Flowpath

I’m not even sure what that means.

[jim]

Hi Dan,

It looks like the DXF export is the main cause of gaps between arc segments that flowpath doesn’t like.

Below is a list of the locations of the last 3 endpoints on the curve you posted.

You can see that the DXF output makes small changes to all the endpoint locations, but the last joint in the curve gets changed the most. The endpoints that Flowpath considers coincident agree to at least 9 decimal places the joint where Flowpath sees a gap the end points only matches to 7 decimal places.

Can you send your curves to Flowpath in IGES format? IGES will output the arcs without changing them.

End Points Before DXF Export:

1389.5719988752571, 4022.1975319927856
1389.5719988752578, 4022.1975319927851

1392.1979533674360, 3795.1739201918194
1392.1979533674312, 3795.1739201918194

1393.6204521863735, 3341.1021489644299
1393.6204521863942, 3341.1021489644299

After DXF Export

1389.5719988752662, 4022.1975319927851
1389.5719988752569, 4022.1975319927856

1392.1979533674312, 3795.1739201918199
1392.1979533674355, 3795.1739201918035

1393.6204521863567, 3341.1021489529021 <–
1393.6204521863910, 3341.1021489643722 <–
______________________________________________________^

[jim]

Did some more checking…

Looks like the cause of the gaps is the “Simplify” option
Try exporting without that box checked.

[lux_wales]

Jim,

Firstly “The arc on the end of your curve has a radius bigger than the radius of the earth.” I’m still chuckling.

Thank you for such a concise and explanatory answer. I have replaced the curves with gigantic radiuses for polylines. Next I will try without simplify and then IGES.

Hopefully find out tomorrow what the dreaded flowPATH thinks.

Again thank you. Really appreciate it.

Dan

[PeterNBiddle]

According to the teacher in the flow class I just attended “Flow doesn’t like splines” and I also had the gap issues that the OP had. The “solution” wound up being a complete redraw using the messed up import as a template and a lot of rubber-banding in Flow.

Meanwhile I’m still having a terrible time with simple 2D objects.

I’m going to post a new topic on the challenges I’ve been having with Rhino and Flow.