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Author Topic: Help - Pocketing problems  (Read 4845 times)

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Offline astr

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Help - Pocketing problems
« on: December 03, 2008, 10:18:19 AM »
Hi,

I've been trying cut a plaque that was created in Autocad.  Most of the milling involves pocketing the letters and symbols.  I've exported the file as an R12 dxf file.  Once loaded into Lazycam, cleaned and optimized, some objects pocket ok, others do not.  I went back and recreated the file with only a few objects that demonstrate my problems.  I've attached both the original dxf and, in the next post, the Lcam results. 
The file contains five objects that I want to pocket.  From left to right, the first object consists of four straight lines and an arc, all connected.  This will not pocket at all.  The second object is a mirror image of the first.  When I first tried to pocket it, it would not pocket like the first object.  When I replaced the arc with a spline in Autocad, Lcam pocketed it OK.  The third object is the form of the letter "S" that was created in Autocad from a series of lines, arcs, and splines.  When I try to pocket it, I get an inside offset but no pocketing.  The forth object (a "Z") is a mirror image of the previous "S", formed by using the Autocad "mirror" function.  This one seems to pocket OK.  The last object, the "S" was created by mirroring the "Z".  I would expect it to have the same troubles as the first "S", but it pockets OK.

What am I doing wrong?

Offline astr

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Re: Help - Pocketing problems
« Reply #1 on: December 03, 2008, 10:24:29 AM »
I've attached here the Lcam file that was the result of the previous test.

PS - Thinking that the problem is based on my use of arcs in Autocad, I went back, and in Object 3, the "S", replaced the arc with a spline.  It still won't pocket correctly.  In fact, it won't pocket at all whereas above it at least created one inside offset.
Re: Help - Pocketing problems
« Reply #2 on: December 03, 2008, 11:35:52 AM »
The curve in the small profile on the laft had overlapping segments.
When corrected, it pocketed well.

RC

Offline astr

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Re: Help - Pocketing problems
« Reply #3 on: December 03, 2008, 11:45:16 AM »
Thanks Overloaded!  I'll give it a try when I get home.

Offline astr

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Re: Help - Pocketing problems
« Reply #4 on: December 05, 2008, 03:52:12 PM »
The curve in the small profile on the laft had overlapping segments.
When corrected, it pocketed well.

RC
I corrected to overlapping lines, as you suggested, and I was able to pocket the first object OK.  I've been playing with the last three "S" objects and can't seem to find any consistent pattern as to when it will not pocket at all, when it does an offset, and when it pockets correctly.  I played with the "Connection Line Tolerance" for opening the file to insure that I always got the "Closed Chain" box checked when I loaded.  I also noticed really crazy results when I tried to do an offset on the same objects that were giving me troubles when pocketing.  I seems that Lcam did not recognize the existence to some of the curves that made up the object.  I'm still very baffled as what is going on.
Re: Help - Pocketing problems
« Reply #5 on: December 06, 2008, 09:14:30 AM »
Seems to work fine here. What is the description of the tool you are using ?
RC

EDIT: Also, LC typically doesn't like splines, you may need to convert them.
« Last Edit: December 06, 2008, 09:16:28 AM by Overloaded »

Offline astr

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Re: Help - Pocketing problems
« Reply #6 on: December 07, 2008, 03:18:57 PM »
Seems to work fine here. What is the description of the tool you are using ?
RC

The tool was an end mill, 1 unit in diameter.

EDIT: Also, LC typically doesn't like splines, you may need to convert them.

I went back into Autocad and replaced all of the splines with arcs, regenerated the dxf, and now both pocketing and offseting seems to work as expected.  I'll have to go back into Autocad and figure out what I can use instead of splines as sometimes arcs won't work well.

Thank you for your help.

Offline ger21

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Re: Help - Pocketing problems
« Reply #7 on: December 07, 2008, 06:55:52 PM »
In AutoCAD, saving as v12 .dxf automatically converts splines to polylines with straight segments. You can also download lisp routines to convert splines to polylines with more control over the segment quantity. Cadalyst magazine has a couple, search for spline to polyline.
http://cadtips.cadalyst.com/
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline astr

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Re: Help - Pocketing problems
« Reply #8 on: December 07, 2008, 07:27:03 PM »
In AutoCAD, saving as v12 .dxf automatically converts splines to polylines with straight segments. You can also download lisp routines to convert splines to polylines with more control over the segment quantity. Cadalyst magazine has a couple, search for spline to polyline.
http://cadtips.cadalyst.com/

I Use Autocad 2007 and have been saving as Autocad R12/LT2 DXF.