Smooth finish (Arc fitting)

[HughesTooling]

I have an old Heidenhain control and arc fitting is very help full at reducing file size. Fusion's arc fitting works quite well but seems to miss some lead arcs.

In this screen grab green are arcs and blue line moves. 

File attached to this thread. This is a back plot of Setup3.

http://forums.autodesk.com/t5/preview-cam/a-couple-of-problems-with-round-stock/td-p/5435203

Thanks Mark.

[innovatenate]

If you could provide the data set, I will be happy to forward the issue onto the relevant parties. Feel free to send me a public link of the design at nathan.chandler@autodesk.com or post the link here.

You may also consider posting this question in the Autodesk CAM forum. 

http://camforum.autodesk.com/

Thanks,

[HughesTooling]

The file is attached at the bottom of my first post here.

http://forums.autodesk.com/t5/preview-cam/a-couple-of-problems-with-round-stock/td-p/5435203

Link to file.

http://forums.autodesk.com/autodesk/attachments/autodesk/2070/243/1/Temp.f3d

Thanks Mark.

[fonsecr · Accepted solution]

Hi Mark,

When using the smoothing feature we currently allow the arcs to be slightly spiral (ie. start and end radius differ). This is to make the toolpath more smooth. The bigger smoothing tolerance, the bigger the spiral effect will be. However, when you post process the toolpath and your CNC does NOT support these moves the post will linearize these moves which is why you get lines.

Now, I do want to improve this so spiral get output less often. On my todo. However there are 2 kinds of arcs the horizontal ones and vertical ones. And the spirals are only a problem for the horizontal arcs. Since all our linking moves are tangential the vertical arcs will generally happen in any planes. Ie. not ZX and YZ as is normally supported for ISO controls. Some controls do support arcs in all planes but the post will linearize these when they are not supported. So you will generally still get linearized arcs. You could turn of the vertical leads but this is not desired - but if you have an old CNC you might not have an option here.

For the horizontal arcs issues you can reduce the issues by using both tighter tolerances and smoothing tolerances. But here it is a tradeoff against your CNC block processing speed.

If your CNC does support spiral moves it is easy to add support for this in the post and you wont have a problem. E.g. the generic HAAS has a setting for tell which big spirals to allow. Note that this is often a setting or hardcoded limit in the CNC also - so you cannot just allow any spirals.

So you can start by finding out if your CNC happens to support spiral moves.

René

[HughesTooling]

Hi René

Thanks for your answer but I'm not seeing the spirals on the lead outs. I've back plotted the g code into another program and drawn a 3 point circle over the lead out and it fits perfectly.

Here's a screen grab.

.

I set lead ins and outs so they are in the XY plane only. The arc fitting is working realy well on all but the lead outs, the lead ins are converted to arcs. In this screen grab blue are lines green arcs.

Each lead outs is generating 25 lines of code and just about doubles the program size. I'll attache the G code, the DXF back plot and the latest f3d file.

Thanks Mark.

[fonsecr]

It would be hard to see the spirals after post processing since the radius difference will be lower than the smoothing tolerance. However, you can post using the Dumper post dump.cps which will write out "spiral" for all spiral motions.

You should still find out how big radius difference your CNC supports. If we add this threshold to your post many spirals might not get linearized.

PS. Did you customize your own post? Because it is somewhat different from our generic Heidenhain ISO post.

[HughesTooling]

The code I posted here was done with a modified Bridgport post for my EZTrak. I have some questions about the post for the EZTrak and Heidenhaid would it be best to goto the CAM forum for that.

Mark.

[fonsecr]

Absolutely, http://camforum.autodesk.com/ has a separate section dedicated to just posts. So this is definitely preferred.