Roughing / Keepout Bug

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Roughing / Keepout Bug

Postby RoughVegabound » Sat Jan 16, 2016 10:06 am

Hello forum members,

I believe I have crossed paths with a very aggravating MeshCAM bug.

Attached to this post should be a file named Assembly2.7z that contains an STL and DXF pair that can be used to reproduce the failure.

I am using MeshCAM 6 Build 27 which I believe is the latest version.

To reproduce the failure...

• Start MeshCAM

• Click Open, select Assembly2.stl, click Open, click 3 Axis to load the part

• Click Define Stock, change X to a much larger value (I use 200), change Y to a much larger value (200), click OK to ensure the stock dimensions are not relevant

• Click Cap Holes, click OK to ensure the single hole is not relevant

• Click Set Machining Region, under Set Keepout Region click DXF, select Assembly2.dxf, click Open to block the four supports

• Click Tools, click Carbide Auto Toolpath, change material to Wood-Hard, change end-mill to #101, change Finish Quality to Higher, ensure Review toolpath settings is not checked, click OK to start calculating a toolpath

• Wait for MeshCAM to finish

The Rough Operation is consistently inside one of the four keepout regions. I have fiddled and fiddled and fiddled. The result is always the same.

I have two other similar parts and a third identical part that all work perfectly.

I have been able to reproduce the problem with STL files generated by Inventor and extruded DXF files generated by AutoSketch.

Changing Machining Margin seems to have the largest affect on the result but has not eliminated the problem.

Occasionally, the Waterline Finishing also falls within the keepout regions.

I have tried the #102, #111, and #112 end-mills.

Any help reproducing the failure, reporting the failure, or working around the failure is greatly appreciated.
Attachments
Assembly2.7z
(241.92 KiB) Downloaded 80 times
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Re: Roughing / Keepout Bug

Postby Randy » Sat Jan 16, 2016 4:08 pm

I suspect a problem with your DXF file. This is what it looks like when I load your stl and dxf

keepout.PNG
keepout.PNG (183.05 KiB) Viewed 1476 times


It appears that there is an overlapping outline on your right two end supports. My 2D CAD program cannot open the file either which indicates that something is wrong. I'd check your DXF carefully to eliminate any overlapping and/or duplicated lines. Recently there was a problem here on the forum with a DXF that had two superimposed circles.

But I must say that is not the way to use MeshCAM IMHO. Just model your part, define a large stock, use Machine Geometry Only with a margin just a little larger than your cutter radius, and use Set Geometry Supports to build the supports. The built-in MeshCAM supports are handled well in MeshCAM (since they are an integral part of the program) and you don't need to use workarounds to avoid machining their outer ends along with the rest of the geometry. Just search supports here on the forum and you'll find many prior examples.

If you do prefer to use keepouts, make sure the outlines are very clean before you export it from your CAD program and you probably won't have a problem there.

Randy
All opinions in this post are mine alone. I am not a MeshCAM employee, I do not have a financial interest in MeshCAM, nor do I speak for MeshCAM. MeshCAM user since Beta 5 in 2003. viewtopic.php?f=11&t=15333 :ugeek:
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Re: Roughing / Keepout Bug

Postby RoughVegabound » Sun Jan 17, 2016 6:46 am

Thank you for the reply.

I'd check your DXF carefully to eliminate any overlapping and/or duplicated lines.


Done and attached. The failure persists.

The built-in MeshCAM supports are handled well in MeshCAM (since they are an integral part of the program)


If supports worked the way I need them to work I would not be on this path.

If I use the most recent DXF to define the machining region only the area inside the pad contains a toolpath. If I use the same DXF to define the keepout region only the area inside the pad contains the rough operation. How is that not a bug in MeshCAM?
Attachments
Assembly2.7z
(223.42 KiB) Downloaded 80 times
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Re: Roughing / Keepout Bug

Postby Randy » Sun Jan 17, 2016 10:28 am

Oh, I'm not saying there might not be a bug in MC. MC has a spotty history where it comes to using DXF's for machining regions, and when I use regions I draw them by hand.

I can trigger the behavior you observe by adjusting the calculation tolerance. I am imagining that you are working in mm, but since STL and DXF are unitless I am taking them to be inches (another quirk of MC is that it tends to get confused when you use mixed inch and mm units) I defined a 2" cutter and specified Machine Geometry Only with a margin of 1.5".

With a calculation tolerance of .050", I get proper roughing behavior

Capture1.PNG
Capture1.PNG (77.87 KiB) Viewed 1461 times

but with a calculation tolerance of .010" I get the behavior you observe

Capture2.PNG
Capture2.PNG (65.17 KiB) Viewed 1461 times

so to answer your question from the first post, try different calculation tolerances. There might be some internal interaction between the machining region boundary handling and the calculation tolerance.

Since you are using keepout regions anyway, you might try extending your modeled supports out into the keepout region, rather than having the region and geometry boundary line-to-line. That might be confusing MC also. I hand-drew a keepout region that ovelapped the right-hand support, and generated a successful roughing toolpath at .010" calculation tolerance.

Capture3.PNG
Capture3.PNG (79.23 KiB) Viewed 1461 times

Out of curiosity, what about MC's built-in supports doesn't work for you?

Randy
All opinions in this post are mine alone. I am not a MeshCAM employee, I do not have a financial interest in MeshCAM, nor do I speak for MeshCAM. MeshCAM user since Beta 5 in 2003. viewtopic.php?f=11&t=15333 :ugeek:
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Re: Roughing / Keepout Bug

Postby RoughVegabound » Sun Jan 17, 2016 10:30 am

Attached is an excellent example of the failure. Both DXF files contain a simple rectangle (closed polyline). The rectangles are identical except the one in Assembly2-Fails.dxf is at a slight angle to the X/Y axes. Both rectangles are the same distance from the part.
Attachments
Assembly2.7z
(101.29 KiB) Downloaded 80 times
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Re: Roughing / Keepout Bug

Postby RoughVegabound » Sun Jan 17, 2016 10:56 am

Thank you for the reply.

Randy wrote:I draw them by hand.


I can't get the precision I need doing them by hand. Plus...

I can rubber-stamp them in the CAD package. With snap-to, aligning, mirroring, translating, saving, reloading and all the other niceties of CAD.

I can include different styles / sizes / shapes in the same design.

I can even trim them smaller using a second pass after the part is complete (i.e. nearly cut the part free).

Out of curiosity, what about MC's built-in supports doesn't work for you?


All of the above plus they pierce all parts in the drawing making it extremely difficult to lay out a sheet of parts.

I am imagining that you are working in mm


I am.

so to answer your question from the first post, try different calculation tolerances


I will try that. Thank you.

What is the implication of using a greater calculation tolerance?

Since you are using keepout regions anyway, you might try extending your modeled supports out into the keepout region


That's how they are normally shaped. I tried to make these drawings as simple as possible to illustrate the failure.

They are normally like a mushroom with a stem and cap. The stem is exactly 1.5 end-mill diameters in length. The beauty of that design is the same stem can be used to create supports between parts.
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Re: Roughing / Keepout Bug

Postby RoughVegabound » Sun Jan 17, 2016 11:03 am

Randy wrote:so to answer your question from the first post, try different calculation tolerances


That was a bust. MeshCAM will not allow me to make it larger than 1.270 mm / 0.050000 in. At that size the failure still occurs. Also fails at the smallest possible value.
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Re: Roughing / Keepout Bug

Postby Randy » Sun Jan 17, 2016 7:17 pm

I'd suggest sending Rob an email at the MC support address and pointing to this thread. I don't know the innards of MC (being just another user) but I can't imagine why a DXF outline would be any different than a hand-drawn outline from the processing perspective.

But unless there are pressing reasons I'd be doing the part like this. I put your STL into MeshLAB and knocked off the modeled supports (other than little funky bits at the bottom which I couldn't cleanly remove) and healed the resulting gaps. I imported as inches, scaled by .0394, created the supports in MC, used a .125" ball-end cutter with an edge margin of .08" and a calculation tolerance of .0005"

Capture.PNG
Capture.PNG (153.61 KiB) Viewed 1446 times

the way I do all my 3D parts.

That brings up another thought--does your problem occur with both flat and ball-end roughing cutters? That might be another clue...

Randy
All opinions in this post are mine alone. I am not a MeshCAM employee, I do not have a financial interest in MeshCAM, nor do I speak for MeshCAM. MeshCAM user since Beta 5 in 2003. viewtopic.php?f=11&t=15333 :ugeek:
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Re: Roughing / Keepout Bug

Postby ArchieF » Mon Jan 18, 2016 4:05 pm

Hi guys,
seems to be an issue with the stock size and selecting Machine Geometry Only or Machine Whole Stock.

Machine Geometry Only but enough stock creates a toolpath within the Keepout Region.
Selecting Machine Whole Stock works perfect.

Using the files in Assembly2.7z and added 3 more Keep Out Regions to play with. Please see the screenshots.

Thanks,
Richard
Attachments
Machine Whole Stock.png
Creates a perfect toolpath
Machine Whole Stock.png (60 KiB) Viewed 1429 times
Machine geometry only.png
Creates a toolpath within the region
Machine geometry only.png (25.45 KiB) Viewed 1429 times
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Re: Roughing / Keepout Bug

Postby RoughVegabound » Thu Jan 21, 2016 11:06 am

Randy, thank you for the reply.

Randy wrote:I'd suggest sending Rob an email at the MC support address and pointing to this thread.


Done.

That brings up another thought--does your problem occur with both flat and ball-end roughing cutters?


The cutter seems to make no difference in regards to this failure.

But unless there are pressing reasons I'd be doing the part like this.


Thank you for the suggestion.

Fortunately, for this project, aligning the keepouts with the X/Y axes stopped the failure from occurring. Even with the supports still in place and a symmetry mistake, the first T-shank handle is working well!
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