Problem Cutting Out Lettering

[chodges]

We have a new PRS Alpha, and today we cut our first lettering job out of Sintra.

The .DXF file we were given by our customer looks perfect, but when we cut the letters out, the curves on letters like a capital "G" look like they are formed by a lot of short straight lines instead of a smooth arc.

Any ideas on what we are doing wrong? We have much yet to learn.

Thanks!

[Brady Watson]

Try selecting the 'ShopBot Arcs Inch' post processor from the dropdown when you save your SBP out of PartWorks. It will give you smoother cuts whenever cutting circles, arcs or curved parts. Try an Onsrud 52-624 for cutting expanded PVC.

-B

[joe]

Brady is correct with the Arch Inch.

Your are correct about the code. That's what it's doing. It's Shopbot Code of little strait line, but Arch Inch. will shorten them up and help some.

[chodges]

What do you do if the "ShopBot Arcs Inch" strategy still produces just about the same results?

When I bring up the .DXF in other software, like AutoCad, Corel, FlexiSign, etc. it looks perfect.

Thanks!

[jhicks]

Charlie, consider the tolerance settings you may have on your software. Depending on how small or large you set the tolerance to follow will impact the tool path your following around the curves and elsewhere.
not sure but this happened to me once and the curves were literally straight line segements vs radius corners.
Might be the problem since it looks like you tried everything else.
Does the tool path preview show the segments you see when cutting or does it look good in preview and turn out bad in cuts?

[chodges]

Thanks Jerry! That sounds like the direction I need to go.

The file I am working with is a .DXF that was provided by my customer. I have tried bringing it into Corel and FlexiSign to re-export it as a .DXF, but I can't find any opportunity to adjust the tolerances. How do you do that?

[henrik_o]

Could you post a picture of what the dxf looks like when rendered in your CAD program?

I get a lot of DXF files that I can't use and have to ask the client to supply a new one with better definition (i.e a higher mesh subdivision). The problem is that many CAD programs 'cheat' and render better than the actual resolution saved in the exported dxf.

To illustrate this, the following picture shows three spheres, the left one using 12 segments, the middle one 24 segments (default), the right one 48 segments, rendered using the default settings;


8096

Now, if I turn off "perfect rendering" in the settings, and render w/ outline, I get a picture that actually shows what will be exported, and now it looks like this:


8097

The left sphere is completely unusable for cutting, the middle one is awful, the right one is bearable but just so.

Since you say the dxf's look great in your CAM program (and I assume you mean they look great when zooming in on them), the above may well not be the problem here, but this is something I personally have to fight constantly.

[beacon14]

This was touched on recently as part of a thread drift so probably impossible to find by searching. I find when drawing curves, arcs and elipses (in DesignCad) they will machine with straight segments UNLESS I convert the curves to vectors before exporting/importing into VCarve.

[chodges]

If I am doing this right, the .DXF file is attached.


DXF File
vining sparks ROUT.dxf (http://www.talkshopbot.com/forum/messages/312/vining_sparks_ROUT-28660.txt) (32.3 k)

I thought .DXF files were vector files, so I don't understand how to convert the curves to vectors.

[robtown]

Charlie this looks like a dxf file that was created by exporting a .dxf from corel. Zoom in in AutoCAD and the segments are fairly visible. Corel is not good with .dxf files, importing or exporting. See if your customer can give and .ai file (illustrator) or .pdf file.

[henrik_o]

The file works and it looks good.

Did changing tolerance in the CAM (as Jerry proposed) work?

If not, do you have a pic of one of the jagged blanks?

[beacon14]

The file opens fine in DesignCad. The straight lines are vectors and the curves are arcs. In DesignCad if I select the curves there is a command to convert the current selection to vectors.

I e-mailed the converted file to you - too large to attach here. Let me know if it works any better.