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Post by spinnaker on Feb 4, 2016 0:36:39 GMT
I downloaded PCBGCode and tried it a few times to create isolation layers. One feature it has is to allow a minimum and maximum isolation width. Based on the width of the tool, the software calculates the number of passes required to produce that width. I am not seeing such a feature in Line Grinder. Does Line Grinder do only one pass or am I missing something? |
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Post by robinmitchell on Feb 4, 2016 9:44:31 GMT
Firstly you will need to know the angle of your milling blade. Then with that you can determine the width of the cut as you a set distance into the material. Its a basic triangle problem where your cut depth is the adjacent, the opposite is half of the cut width and the angle between the hypotenuse and the opposite is half of the blade angle. For example see the image below:  This blade has an angle of 20 degrees between the two sides. If we want a cut width of 1mm the required depth into the material would be as follows: O = Half cut width A = Cut Depth angle = Half blade angle Angle and O are half because you are cutting the blade in half (to make the calc easier) tan ( angle ) = O / A A = O / tan ( angle) A = 0.5 / tan ( 10 ) = 2.835 mm cut depth Typically in milling you need to shave at least 40uM off as the copper is 35uM so a cut depth of at least 0.2mm is going to be sufficient. So, LineGrinder only does one pass! You just enter the cut width and the depth which the isolation blade should cut and it will do the rest. To be honest multiple passes is a waste of time because the only function of isolation cuts is to isolate copper  Robin
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Post by spinnaker on Feb 5, 2016 0:27:44 GMT
I would think a 1mm tool is moving a lot of material at once. A smaller bit would require less stress on the machine. True? And isn't the idea to mill off as little fiberglass as possible? I do not understand the value of calculating the cut depth based off of the size of the tool. I do understand calculating actual tool width size based on the angle of the bit as this calculator shows. woodworkerb.com/home/pcb-isolation-routing/tool-width-calculator/This site also allows for multiple passes to create a wider separation. rapid-pcb.com/I would think you would want a bit more isolation than a .1mm width. |
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Post by robinmitchell on Feb 5, 2016 16:50:35 GMT
I have not done the math but when I do cuttings on my machine with the bit I have 0.2 to 0.4mm depth cut is sufficient. Isolation routing is something that I do not do but I do v-scores where both sides of the material are cut into lines. Believe it or not but you can cut as much as you want! What then matters is the FEEDRATE. This is a very important number because it tells the machine how fast to move the axis. For example, when I drill into material the feedrate is maximum (700), and when I vscore the feedrate on the xy axis is 1000 (half the max speed). When I used to do tab routing the feedrate was as low as 80! Your right about the 0.1mm but I have not done the math! The smallest I suggest is 0.254mm (10mil) but the depth depends on your bit. You say you do not understand the depth calculation which is fine because it is difficult to explain without a diagram but to help you just tell me the angle of your bit and I can do the rest and show you how I did it  Robin |
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Post by spinnaker on Feb 6, 2016 1:12:28 GMT
I think I might b able to under stand the formula. I just am having trouble understanding the value of calculating depth to get a desired width.
And I do not understand this statement "Isolation routing is something that I do not do". Isn't that what you are doing with linegrinder?
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Post by dnarobotics on Feb 6, 2016 3:15:45 GMT
My first board made with Eagle 6.4.0 and used pcb-gcode-3.6.0.4 to generate single pass G-code to engrave & drill with Mach3Mill I cut very shallow. It had traces running between DIP pins. The cuts were so narrow that it was very hard to solder without bridging to other traces. You can see most of my stuff here: forum.allaboutcircuits.com/threads/milling-pcbs.118705/page-3#post-940394 |
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Post by robinmitchell on Feb 6, 2016 9:08:00 GMT
I think I might b able to under stand the formula. I just am having trouble understanding the value of calculating depth to get a desired width. And I do not understand this statement "Isolation routing is something that I do not do". Isn't that what you are doing with linegrinder? I use linegrinder for converting excellon drill files, creating tab routes for a single PCB and v-score cuts for panel designs. The Vscore cuts are technically isolation cuts but I set the bit width as small as it can be so it makes the smallest isolation cut possible. OK so lets say that you want an isolation width (distance between copper to copper), to be 10mil which is 0.254mm. Lets also say that you have a 60 degree bit. This is how deep you need to cut: Angle = 60 Degrees Bit
Width = 0.254mm
Divide the bit down the middle to get two right angled triangles (makes the math easier)!
Triangles opposite = Distance from the edge of the angled blade to the center of the blade. This is half the cutting width
Triangles adjacent = Depth of the bit into the PCB material
Triangles angle = Angle between the hypotenuse and adjacent. This is HALF of the cutting angle because you split the blade in half
Tan(angle) = (O / A)
Tan(30) = (0.1252 / A)
Rearrange:
A = 0.1252 / Tan (30) = 0.21685mm
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