Splines

[spalm]

What am I doing wrong? I have been playing with Sheetcam for a while now, but I keep running into this problem. Attached is a simple drawing of a gantry side. I want to finally add some curves, but I can not get Sheetcam to see it. I believe that it can. The drawing is ugly, but only has a three point spline to keep it simple for now. Sheetcam does not display the spline.

Steve

[ger21]

Steve, stay away from using splines. Far away. I'm not familiar with any CAM software that reads can read them. Nothing inexpensive, anyway. I converted it to a polyline for you.

[Moondog]

Steve....

We use splines all the time for curves. Basically use Polylines for straight pieces and splines for curves. Never had any problems.... Maybe Sheetcam doesn't like Splines. Do you have an option to use Bezier curves instead?..

As far as I know most Cam programs can read splines.

cheers

Frans

[ger21]

Frans, you use AlphaCAM, right? Do you know of any CAM software under $1000 (under $500 maybe?) that can read splines?

Does Alphacam output G1 moves, or G2/G3 moves for the splines?

Steve, if Xpress could save as V12 .dxf's, the splines would automatically be converted. Unfortunately, it doesn't. I'm pretty sure all the CAM programs that can read splines, just convert them to polylines internally. I think I read that Les plans on adding spline support in the future, but I might be mistaken. I think your only option now is to not use them, unless you have a way to convert them. If you really need to use them, I can do the conversions for you. It's not a big deal.

[spalm]

Thanks guys. I get it now. Since there is no Spline command for standard Gcode (Mach III style), it needs to be converted into polylines (hundreds of line segments). I could see where a more costly CAM system could handle this by itself.

You are right Gerry; Express does not seem have any way to output its curves as polylines. What is the command in AutoCAD to convert (PEDIT or something linke that?).

I think I will try to stay with straight lines and fillets, as these will turn into native commands in Gcode.

Steve

[ger21]

Originally Posted by spalm What is the command in AutoCAD to convert (PEDIT or something linke that?).

There are 2 Autolisp routines to convert splines to polylines available from Cadalyst magazine. One from December, 2003 and one from June, 2005.
http://new.cadalyst.com/code/

I use the 2003 one. It will convert 3D splines into 3D polylines. Not sure if the other one does, but I've heard it may work better with 2D splines.

[locost_cam]

I am working on splines in DXF files. In fact the EMF import already supports splines. If your cad package has the option of EMF export then try it and see it it works for you.
As G-code cannot handle splines all splines will be converted to polylines. If possible you should try to stick to arcs.

Les

[sdantonio]

Hi Gerry,

This conversion from splines to polylines you talk about. Does this conversion also have to be done for b-splines (NURBS) generated from drawing produced in Rhino3D? Or are they handled differently than standard splines by CAM software (RhinoCAM, MeshCAM or SheetCAM)?

Steven

[ger21]

Originally Posted by sdantonio Hi Gerry, This conversion from splines to polylines you talk about. Does this conversion also have to be done for b-splines (NURBS) generated from drawing produced in Rhino3D? Or are they handled differently than standard splines by CAM software (RhinoCAM, MeshCAM or SheetCAM)? Steven

I'm pretty sure Rhino can do it automatically during .dxf export, if the correct options are selected. There may also be native Rhino commands to convert, but I don't use it regularly so I'm not sure.

Just remembered. Version 12 .dxf files don't support splines or nurbs, so they have to be converted when you use that format.

[locost_cam]

Originally Posted by ger21 Just remembered. Version 12 .dxf files don't support splines or nurbs, so they have to be converted when you use that format.

That's right Gerry. I always recommend that you use V12 or earlier for this very reason. Unfortunately not all cad packages support different DXF version.

Les

[spalm]

Les,

Thanks for a great product.

Alibre does have EMF export, and the lowest DXF is V1.4. How do I use EMF import? I don’t see it as a viable option in SheetCam V2.0.3.

Steve

[locost_cam]

Originally Posted by spalm Alibre does have EMF export, and the lowest DXF is V1.4. How do I use EMF import? I don’t see it as a viable option in SheetCam V2.0.3.

Have you tried V1.4? It may work. SheetCam V2.0.3 does not have EMF. You have to change to the development version for this.

Les