Text conversion...Rhino to CAM


#1

Hi Gang:
I exported a simple 2D line drawing with text from Rhino V5 to a .dxf for a maching process on a CNC router. The lines/curves exported fine but the text was a problem when the machinists CAM software imported this file. The font was altered and the position and relative position of the characters was altered. I’d like to discuss this problem with the machinist but first wondering if anyone on this forum has tips for exporting to .dxf format so that text conversion is faithfully replicated on the CAM side. I do not know what CAM software is being used. Just wondering if anyone else has had this problem and what corrective action is advised. Thanks.
Cornbelt
01 Aug 14


(John Brock) #2

Were these actual text or did you use the TextObject command that makes curves from the fonts? For machining, you would want to do the latter so it looks like text but really are curves.


#3

It’s been our experience, in these types of applications, that IGES format (configured NOT to create splines) is superior to DXF. This would include wireEDM, waterjet, laser cutting and engraving on 3 and 5 axis CNC machines.

I would ask if your machinist’s software can accept IGES.

Dan


#4

John, these were actual text, not text object. Good hint. Thanks.
Cornbelt


#5

DanBayn, i’ll bring this up with the local machinist. Thanks for the tip.
Cornbelt


#6

Hi John:


#7

Hi John, i found a single stroke font offered by MecSoft, installed on my computer and was able to used as a text object in Rhino V5. These characters are all curves so i think the engraving operation at the machine shop will be successful, i.e., 1:1 transfer from Rhino file/iges file (per DanByn) to machined product.
Thanks again
Cornbelt


#8

Cornbelt,

I’m no expert, but this is actually a bit more complicated than it seems. Lots of CAM programs can use DXF files, probably fewer accept IGES, as mentioned consult your machinist. DXF is a proprietary Autocad file format, and they change the definition from time to time, so there are many flavors of DXF. The CAM output will vary depending on the scheme chosen. When you export to a DXF you will get an options pop-up from which you can choose a number of schemes (I’ve had good luck with R12 Lines & Arcs), and you can furthermore edit these schemes with regard to how they parse particular geometry objects. If you do use DXF, you may need to show these option screens to the machinist and experiment a bit to get it right.


#9

I’ve never run into a CAM program that doesn’t read IGES curves.

The point here is that Rhino’s DXF output is uinreliable while the Rhino IGES output is rock solid.
If you want to the CAM programmer to see the same thing that you see in Rhino use IGES.


(John Brock) #10

Horsefeathers.
Rhino’s DXF output IS reliable.
I think the issue here is DXF does not support anything like a NURBS curve. It has to be approximated with a chain of arcs before exporting or approximated with a series of faceted polyline segments.

IGES files do support the equivalent of a NURBS curve.
With DXF, the Rhino user is doing the conversion to G-Code compatible lines and arcs.
With IGES, the CAM application is doing the arc and line segment conversion internally.

Good luck


#11

Most CAM programs can read IGES nurbs and not having the data converted into something else alone makes sending it by IGES more reliable.

The problem the original poster reported sounds like numerous other complaints about DXF that I’ve read over the years. Now I’m not saying he won’t be able to get it to work with DXF. If he spends enough time, energy and experimentation with his machinist he will probably eventually get it to work. But that doesn’t fit my definition of reliable.


(John Brock) #12

NURBS and spline curves must be converted to Arcs and Lines since that’s all G-Code supports. The question then becomes where does the conversion occur. Since CAM applications pass DXF curves without converting them, then the conversion burdon from NURBS or spline curves to arcs and lines is on the user. Try sending an AutoCAD Spline curve out through DXF. Your CAM application will ignore it.

The better CAM applications that can read IGES files will do the conversion to g-code arcs and lines on the fly and do a good job of it.

My point was taking exception to Rhino’s ability to make DXF files. The problem is not with Rhino, it is generally with a inexperienced user not having a deep understanding of the process and how it works.
I too agree that spending a little more on a stand-alone CAM application that accepts IGES files is the best approach. For those with tighter budgets, they can be excellent results too but they may have to work at it a little harder.