My approach was a straight plunge.

The lines I was cutting were often multiple line segments, which I tried to clean up, convert to arcs, etc. but a crop circle would still sneak in on me occasionally. I used cleanup and optimize, which helped a little in some instances, but I did a sign using and Old English font, which drove it crazy. The crop circle (term used on their forum) was a random event. It you could have two identical letters and it would have a problem with one and not the other.

I found that in every case there would be an errant line of code that was easily identified. I wrote a program that would read the GCode file, identify the bad lines of code, and eliminate them. I just got tired of jumping through so many hoops for a simple 2D cut path.

The only thing I used BobCAD for was GCode generation. I do all of my CAD work in AutoCAD. BobCAD's CAD program was atrocious. It was very clumsy, non-intuitive, and generally poorly conceived. I was using version 20, and BobCAD's people told me that some of this was addressed in the newer versions, but they wanted more for the upgrade than I paid for VCarve Pro, and it has yet to have a single glitch. So far, I think I made a good decision on switching, and am looking forward to upgrading to Aspire when I can afford it.

Thanks for the further explantion.  I agree that the learning curve on BobCad is steep - very steep.  Has BoobCad every addressed the issue?  Or did they try to upgrade you?  LOL.  

One other question.  What post processor do you use in BoobCad?  Forgive me - but I've had some bad experiences using the applicaton too.  I'd tell you about them, but dragging up the old memories is just to brutal!

The 'crop circle' issue seems to be one that has gone back for several releases. If you look on their support forum and use the search term 'crop circle' you will find MANY messages relating to this issue. The last contact I had with them stated that many of these issues have been addressed in later releases (again, I was using version 20 and they are up to 23). They wanted me to upgrade to (maybe) correct these problems (for the upgrade price of $800.00 or more).

I was using a Mach3 post processor.

As to the learning curve on BobCAD, that wasn't my issue, it was the clumsiness and unnecessary selections. For instance:

In BobCAD, to 'MOVE' an object you have to select the objects, then click on 'Change' then 'Translate' (what the hell does that mean, I want to MOVE an object), then select the method. You can select 'Increment' then enter an X coordinate ,then a Y coordinate, then OK to move it, or select 'Snap' and select the snap coordinates, etc.. In AutoCAD you select the objects, right-click, select 'Move', then you can (for increment) just type '@1,1' to move it over 1 and  up 1 , or click on any 'snap' point and select another snap point and it is moved, or you can enter the new coordinates. All with a single mouse click and some typing.

In BobCAD, to trim/extend an object you go through the same thing. Several menu selections to get to the point that you can trim/extend anything. In AutoCAD you simple select trim or extend, select the trim/extend lines, the proceed to trim/extend as many objects as you want.

My biggest peeve is that in BobCAD the scroll button acts as a PAN function which is worthless (there may be a way to change this but I was never able to find it in their 'documentation'). In most other programs the scroll button acts as a zoom in/out. When trying to create a GCode file from BobCAD it would often not see a string as complete (usually a .005 or less gap in the string). I had to zoom in to EVERY intersection many times to find the break. Since the scroll button acted as a 'PAN' instead of 'ZOOM' I had to continually 'CROP' the intersection, zoom in, crop again, zoom in, etc. sometimes as many as 6 or 8 times to find the break. In AutoCAD I put my cursor on the intersection and used the scroll button to zoom in as much as necessary.

Don't get me wrong, BobCAD worked for me for several years. I used it from 2003 until just recently, but the more complex my drawings got the more glitches I found and the more work I had to do to get them to work without destroying material. I think the 'crop circles' were just the final straw to get me to find something better for my purposes. So far, VCarve has answered that. I have yet to have a single cut error using VCarve, and I'm cutting MUCH more complex drawings than I ever did with BobCAD.

Ken

Can't speak of BobCad since I have not used it since Ver 17  which was a long time ago.
You may want to take a look at a tutorial in Memebers Docs  called ARC Motion. ALthough
is was done specificaly for the lathe there is a lot of general information which pertains to a mill also.

Crop circles are covered rather in depth, and for the mill, you can change the programs shown for  G17
along with the replacing the Z with Y.  You need to have the correct Cam and Mach configuration
for things to turn out correctly. Take a good read of the info and you'll be able to identify and fix almost any crop
circle problem you come across. Unfortunately the Cad / Cam problem is a different story as all the programs have their quirks.
FWIW,
RICH

I'm new at this game, but I feel I've come a long way in a short time.  I got BobCad originally V23 and find the same issues with moving objects.  I have read the other posts on crop circles (G0/G3).  I've just never had it happen to me (yet).  Of course I only use bobcad for "technical" drawings - lots of straight lines and an arc or two.  For complex work I'm using vcarve pro 5, cut 3d and aspire.

I really appreciate you taking the time to write such a lengthy explanaton.  It helps me (us) understand the code better.  Thanks again!

It's true that all software has it's glitches and quirks. As you said, once I knew what to call the problem (I found the crop circle reference after describing the problem on the board) I found PLENTY of information on them. This fact in itself would indicate that it is a problem that should have been addressed long ago. Oddly, the crop circles aren't even the real glitch, I'm sure there is a mathematical reason that the program sees these line segments as circles. The real glitch is the fact that they don't show up in the cut path, you only find them in the middle of a part when it destroys your work.

kthomson,

'Oddly, the crop circles aren't even the real glitch, I'm sure there is a mathematical reason that the program sees these line segments as circles.
'
......There are explainations in the ARC Motion tutorial that address this.


"The real glitch is the fact that they don't show up in the cut path, you only find them in the middle of a part when it destroys your work."

......Wise to always dry run.


RICH