Topics

Calculating Isolation Distance

scott.goldthwaite@...
 

I'm not clear on the Min and Max isolation settings.  The example in the PDF (http://www.johnjohnson.info/wp-content/uploads/2013/05/pcbgcode.pdf) section 3.2 uses 0.010" min isolation distance and tool diameter 0.005".  It says the min distance between two pads is 0.010 + 0.010 + 0.005 = 0.25".  But if the min isolation distance is 0.010", wouldn't the closest the pads could be is 0.010"? 


I would have thought min isolation value is the smallest distance you want two traces (or pads) to be from one another.  For example if I had two traces that were 0.01" apart and my min isolation was also 0.01", then this should just make it.  

But the formula in the manual has isolation = dia + min + step x  passes

So is isolation the "extra" copper that's milled off after the first pass?


For the maximum, will pcb-gcode just keep milling until it reaches the max isolation - unless a trace or pad is in the way?  If my tool is 0.005 and my max isolation is 0.020.  Is 0.020" of copper removed or is 0.025" of copper removed?


I'm sure I'm misunderstanding this and I'm looking for some clarification.

 

 

John Johnson <john6060842@...>
 

Thanks for checking the manual first :-)

The terminology and parameters are based on the way Eagle creates polygons, such as pours.
Isolation is the distance from a trace/pad/via (trace) and the outside of the created polygon. Width is the minimum width of any part of that polygon. So in the attached screen shot, the Isolate parameter is set for 0.013", and the width is set for 0.012", and the two pads will be cut between by the tool. Increasing Isolate to 0.014" results in the portion between the pads being omitted, as it is less than the 0.012" required width.

Assuming one pass or the first pass, in pcb-gcode Isolate is set to the min setting, and Width is set to the tool size. In order for the tool to be able to make two passes between the pads (once around each pad), Isolate has to be twice the minimum plus the Width parameter.

In theory, one could set the tool size to something very small, like 0.001", and the minimum isolate to half the diameter of the cut width of the tool used, and one might be able to leave the cut width+0.001" between features.

This is probably not ideal, but with thousands of users, I don't foresee a change in the operation and potentially making life difficult for all the existing users.

Hope this helps,
John

?-circles represent path of etching tool


Isolate increased to 0.014". Not enough room for 2xIsolate+Width, so pads will not be cut between.



On Sun, May 18, 2014 at 12:20 PM, scott.goldthwaite@... [pcb-gcode] <pcb-gcode@...> wrote:
 

I'm not clear on the Min and Max isolation settings.  The example in the PDF (http://www.johnjohnson.info/wp-content/uploads/2013/05/pcbgcode.pdf) section 3.2 uses 0.010" min isolation distance and tool diameter 0.005".  It says the min distance between two pads is 0.010 + 0.010 + 0.005 = 0.25".  But if the min isolation distance is 0.010", wouldn't the closest the pads could be is 0.010"? 


I would have thought min isolation value is the smallest distance you want two traces (or pads) to be from one another.  For example if I had two traces that were 0.01" apart and my min isolation was also 0.01", then this should just make it.  

But the formula in the manual has isolation = dia + min + step x  passes

So is isolation the "extra" copper that's milled off after the first pass?


For the maximum, will pcb-gcode just keep milling until it reaches the max isolation - unless a trace or pad is in the way?  If my tool is 0.005 and my max isolation is 0.020.  Is 0.020" of copper removed or is 0.025" of copper removed?


I'm sure I'm misunderstanding this and I'm looking for some clarification.

 

 




--
Sent from a MacBook Pro

scott.goldthwaite@...
 

Your images are not showing up.

Art Eckstein
 

Just to let you know, they showed up here!

At 09:33 PM 5/18/2014, you wrote:


Your images are not showing up.

John Johnson <john6060842@...>
 

Maybe Yahoo! doesn't like pngs. Here are jpgs.





On Sun, May 18, 2014 at 9:33 PM, scott.goldthwaite@... [pcb-gcode] <pcb-gcode@...> wrote:
 

Your images are not showing up.




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Sent from a MacBook Pro

John Johnson <john6060842@...>
 

Thanks, Art.


On Mon, May 19, 2014 at 7:57 AM, Art Eckstein art.eckstein@... [pcb-gcode] <pcb-gcode@...> wrote:
 

Just to let you know, they showed up here!



At 09:33 PM 5/18/2014, you wrote:

>Your images are not showing up.
>
>




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scott.goldthwaite@...
 

I  just noticed the images did show up in my email.  But in Yahoo Groups I tried two browsers and they didn't work in either.  Strange.

scott.goldthwaite@...
 

I took a look at the images in my email program.  It's strange I can't see them in my browser.  I can't see the jpg either.  I've tried IE, Chrome, Firefox and Safari.

Anyway, regarding the min distance.  It sounds like pcb-gcode will remove any slivers of copper that are less then the minimum. Is that right?  If so, is the purpose of this just to get rid of the thin copper strips.  I've noticed the thin copper strips can get pushed around - which could be bad.

For max distance, this is the width of the copper removed (ignoring min for the moment).  If the width was 0.020, pcb-gcode will keep taking passes until it removes 0.020" of copper (assuming nothing is in the way).

Let's see if I'm thinking about this correctly: For example, if min = 0.010, max = 0.020 and I have two traces where the distance between them is 0.045", then pcb-gcode will mill a gap of 0.020" around each one.  This would leave a 0.005" sliver between the two.  Since this sliver is less then the 0.010" min, pcb-gode will also mill that out.
If my bit diameter is 0.010 and step size is 0.005, then the first pass it will mill out 0.010 around each trace, the second pass will take out 0.005 more, so the gap is now 0.015, the third pass will take another 0.005, so the gap is now at the 0.020 max, then it will take a 4th pass to mill out the 0.005 sliver that was left.