Letters / Circles for CNC cut out

[Jeroen - Company Call]

Hi all

 

Second time in a year I’m facing the issue that I have to create a DWG for a CNC machine.

 

the DWG is not the issue 🙂 

it’s the text and most of it: all the circles that the text to polyline creates. When exporting to DWG all the circles become small lines which makes it unusable for the CNC machine.

Can someone please explain what the workflow should be?  
How do other people avoid this issue? 
 

Thanks!

[VIRTUALENVIRONS]

I mostly export STL files.  

I think if you explain your workflow from start to finish, you will get better answers. 

[Jeff Prince]

4 hours ago, Jeroen - Company Call said:

Hi all

 

Second time in a year I’m facing the issue that I have to create a DWG for a CNC machine.

 

the DWG is not the issue 🙂 

it’s the text and most of it: all the circles that the text to polyline creates. When exporting to DWG all the circles become small lines which makes it unusable for the CNC machine.

Can someone please explain what the workflow should be?  
How do other people avoid this issue? 
 

Thanks!

 

It is most likely you DWG export settings or the Font that are causing the problem.  See the attached settings that should be successful.

 

Selecting "Approximate polylines with spline type vertices using arcs" is particularly problematic, for obvious reasons.  You don't actually have to have the "flatten 2D" checked, I just forgot to uncheck it before making the screenshot.  If you post your file, I'm sure somebody might take a look and see if there is something in what you did that is causing the issue.

 

 

[markdd]

Try exporting to DXF. That normally is the preferred route.

[Benson Shaw]

I used to do this a bunch. Font designers use bezier curves. As you noted, Text to Poly makes many little arcs to approximate the bez curves.

 

You might have some luck applying the Simplify Poly command. I never did.
 

My solution was to trace the font with vwx polyline tool in arc or tangent arc mode, switching to corner point as needed. This is an approximation, but so is the Text to poly. The trace has only a few vertices compared to the Text to Poly, and since it is all arcs and lines, the dwg is very clean. Downside is all the work with the trace and subsequent kerning and other typography adjustments. I drew a box around each letter as a placement/alignment guide, classed to shut off for the export to dwg. Or some other way to support the unattached areas.

 

Are you cutting letters/numbers? Or holes that have shape of the letters?  If holes, then a little bridge or two is needed to support the inner shapes of characters with holes in them ( eg a, g, e, 4,9,0 etc) - stencil, essentially. 
 

Also, check with your cnc service.  Maybe their software can read the bezier curves allowing fonts in .doc or txt or other format rather than dxf. 
 

-B
 

 

Edited May 10 by Benson Shaw
Longing for clarity!

[Jeroen - Company Call]

Hi hi

 

Thanks for the suggestions all!

 

So far not winning...Tried the export settings but already had them like that.

Please see the file in attachment.

 

If you open the file in AutoCad you will see the circle consists out of many little lines. 

Which causes the CNC machine to stop every time...

 

Hope somebody can help me with a solution. 

CNC Work - VWF.vwx

[markdd]

Using Jeff's suggestion of enabling the Approximate Polylines...... settings works for me.

 

Here is the result I got.

CNC Work - VWF.dwg

[VIRTUALENVIRONS]

@Jeroen - Company Call  Have you tried extruding your letters to a "0" thickness and then exporting.  When I do this all the lines disappear except for 4 control points.

 

Did a test with one letter below.

 

[P Retondo]

CNC should have no problem dealing with a shape consisting line segments. That is how CNC breaks down complex shapes.  So I assume that what you mean by “doesn’t work” is that the resulting letter shapes are jagged and segmented instead of appearing smoothly curved.  Is that correct?  If so, your problem is a matter of scale.  Scaling up a small letter consisting of relatively unnoticeable segments will result in a shape with very noticeable segments.

[propstuff]

Cam software has always, historically, had problems with splines. Newer software can manage them correctly, but there are still sometimes problems with them being converted into the hundreds of little straight line segments you have seen.

For arcs, and circles this should not be the case. The G codes G02, and G03 are "circular interpolation" commands and the machine reading these commands should move smoothly in a continuous arc for the specified dimensions with perhaps a little "hiccup" at the end of the Arc section, where it starts into the next section of the poly line.

If you export a "polyline to text" object where the font element has been made of splines, the DXF export should contain splines. These may present the problem to the cam software interpretation.

Where you export a spline based polyline with the "approximate to arcs" option selected you should get a poly line made up of arc and straight segments. However, there will be many more short arc segments required to make a close approximation of the spline curves. Then you may again encounter the "stuttering" behaviour from the Cam machine as it begins and ends each arc segment.

 

If you are sending a DXF with a shape truly made of arc segments, the cam software should convert the arc elements into GO2, or GO3 interpolated arc commands and the machine should move smoothly for the duration of those arcs. If, on the other hand, those arc segments are being broken up into a series of short straight lines, then the problem is with your cam software.

You can test this by drawing say, a semicircle in vector works, then export it as a DXF. It should still be a semicircle or perhaps an arc in AutoCAD or equivalent. If you then send that DXF file to your Cam software and compile the code for cutting that shape, what you should get is very simple G02 or G03 commands. If you get a whole lot of short G01 (straight line) commands the problem is the way your CAM software is writing code.

HTH

 

BTW, I exported the ( male/ female?) symbols from your file, as well as one of your letter polylines, as DXF to test.

They exported correctly as spline/arc polylines not as lots of straight lines at my end.

As well as much CAM software, older versions of AutoCAD couldn't handle splines at all and turned them into a bazillion straight line segments, but more recent versions of AutoCAD shouldn't  have this problem...

Edited Tuesday at 06:26 AM by propstuff

[P Retondo]

G-code is a language for entering geometry, but at the machine level a series of target points are created.  These points are very close together, so although point-to-point tool movement is a straight line segment, it looks like a smooth curve when executed because the target points are very close together, and also because of motor control latency.  VW does a similar thing when it converts a polyline to 3D geometry (or even to screen output), which is why when you zoom in those shapes look like a segmented polyline.  You can check this by creating an arc, then converting it to a 3D poly, and editing - see all the little vertices.  If you scale such an object, the line segments will get big, and CNC will follow the lines instead of following the mathematical curve you started with.

 

Sounds like propstuff has a handle on your issue, you should try to figure out why his conversion is succeeding and yours is not.

[propstuff]

I had another look at this and re-imported the DXF with Arc Approximation selected. First pic.

As expected there were lots of verticies: 150 or so. Looking closer I noticed some clusters. second pic.

Zooming closer revealed these. third pic

The sequence of this cluster was Arc vertex, corner, corner, corner, Arc.  You'll note in the scale bar these are tiny "increments".

So; definitely undesirable.

 

This seems to be an unfortunate side effect of the algorithm that is making the approximation.

Unfortunately, also, the Simplify Polys command wasn't able to clean it up enough.

 

I spoke to a colleague who has an industrial router and professional CAM software, and he said sometimes files come in clean (from various software origins), and sometimes they are a mess like this. He couldn't predict which or why.

 

With my cheap and cheerful CAM software and homemade router, when I have problems like this I sometimes go through and manually edit the verticies. This is 1; a PITA, and 2; sometimes causes tangent discontinuities from deleting the wrong vertices.

I find a quicker, cleaner option is to just manually trace splines (or freehand artwork etc) using the Tangent Arc Polyline option.

It's not as quick as just clicking a button, but I get clean simple arc-based polys which translate to CAM very well.

 

In the enclosed file is a trace that took about a minute to do overlaid on the original so you can see the fidelity.

It could be made closer with another go and some more vertices, but for your purposes it could be all the accuracy you need.

 

CNC Works R traced .vwx

[P Retondo]

Very interesting, propstuff!  I’m afraid you and I are the only ones interested in this discussion, I note the original poster has gone silent.  We still don’t know the details of their issue.

[VIRTUALENVIRONS]

1 minute ago, P Retondo said:

I note the original poster has gone silent.

As is so often the case.  
 

Although I build for printers, I have not sent anything to a cnc for 35 years.  But, if one of you has access to modern cnc, can you see if my suggestion works or not.  Extrude the letters to "0" and the lines disappear.

[P Retondo]

Not sure if this adds anything to the discussion, but here's an interesting experiment:

Black is letter converted from Text to Polyline, using the VW tool for that purpose.  Note limited vertices, most of which appear to be bezier curves.  Red is the polyline extruded to 0.  It will have no edit handles because it is an extrude.  Green is the extrude converted to a polygon, in which all the segments are lines.

 

If I export as a .dwg, then import back into VW, things are the same, except the red extrude becomes a NURBS surface.  So, the procedure chosen to process the letter creates a significant difference, but perhaps not significant enough to affect the CNC product.  3d Conversion Resolution affects the number of segments in the converted polygon, by a factor of about 2 from "low" to "very high."  Also, I would check to see if the polyline or polygon is "closed" (see OIP), as some manipulations I tried did create an unclosed polygon.

[propstuff]

5 hours ago, P Retondo said:

Very interesting, propstuff!  I’m afraid you and I are the only ones interested in this discussion, I note the original poster has gone silent.  We still don’t know the details of their issue.

Well Pete, it's something I have to do on a semi regular basis, for both routing, and LASER cutting, even though I'm sort of semi retired....

So I'm invested.🙂

My collegue who is running Vectrics software on his machine said it will take an EPS from Illustrator and deal with it happily, but often not a Bezier spline poly from Autocad. (?)

For some reason VW has never exported EPS files as vectors, only bitmap images, so I've never been able to try that route.

[Benson Shaw]

Something I would add to this is the CNC software.  Some services have not updated in decades? and require dxf from customers because AutoCAD light was affordable and other software was/is not. Never upgraded. So success and cost might depend on whether the file from customer matches the capability of the shop. Newer machines and software seem to handle a lot more complexity and variety of input.

 

"My" long time water jet service invested in "front end" software which was quite lenient compared to other shops I tried, although it still did not want bezier curves. My best outcome, though, was always from polylines with only arcs and straight lines, hence my willingness to trace.  I developed arc based polyline alphabets from several fonts. Most were modified to some form of stencil-like characters, but also a few for cutout letters without the stencil bridges and gaps. No stacked points in these characters. Vertex count manageable.

 

The CNC router service I used offered an up to date setup. Owner was a vwx user which meant my native vwx was the input I sent.  He ported to dwg and the slicing app.  Software could interpret beziers, and did z steps for more sculptural objects. A breeze compared to the water jet.

 

-B

 

 

 

 

Edited yesterday at 06:25 AM by Benson Shaw
poly wanna cracker?

[bcd]

 I would also give DWF a try. It can give surprisingly good results.