Saturdays are CNC setup days (part 3)

Some serious progress....

iPhone photo - 0.2mm 30 degree vbit

After dinner with the family I went back to my office (radio room, work office, home office, man cave, etc) and fired up Eagle again. I used the same board example and output two versions of the board to support a 0.2mm 30 degree vbit.

The reason that I created two files is that I wanted to compare the output with different settings from the Eagle - PCBGCode ULP (v3.6.0.1).   There are a couple of ways to setup the isolation cut messurements within the software.  (In the end both worked the same at the mill when I ran the boards.)

iPhone photo - CNC mill for making PCB prototypes

My mill is nothing overly magical. The table moves on the X/Y axis with two stepper motors and the tool moves in the Z axis with a stepper. In my case I using a Dremel model 395 (ebay) because it fits the mount for my mill. I bought the mill in the summer of 2012 at a hamfest in St Paul, MN. (Tailgate Swap Fest)   The table has holes drilled every 0.5" and tapped for 4-40 screws. There some basic clamps that are held down with 4-40 screws. The grid can also be used to zero and align the board for two sided work. (I tested that a couple of weeks ago and it does work pretty easily if you think through your steps.)

Some common vbit sizes

Part of the magic if you want to work with small parts, tight density, or surface mount parts (SMD/SMT) is that you need to know the width of your bit @ the cutting depth and have some idea of the run out (wobble) on your system.

The test board that I laid out in Eagle and have been using for a couple of weeks has traces from 0.001" to 0.025" laid out 0.050" on center. I am able to hold 0.001 / 0.002" traces if I can figure out tooling width. (I would never actually work with traces that small in the real world.)  The short story is the you change the tool (bit) width in the software and keep re-running the board until you stop over cutting (erasing) your trace. Your are basically backing into your measurement with real world tests. Once you understand the bit size it is pretty easy to setup in the software.

Last weekend while I was out of town I was doing some online reading and found a spreadsheet that someone had started to figure out the approximate tool size. The table (above) shows what common bit sizes should cut at a depth of 0.004" which is what my system is setup for.

iPhone photo - 0.2mm 30 degree vbit

I am having really good results with a 0.2mm 30 degree vbit. In fact I might be cutting a little too deep. It appears that it is cutting an isolation trace of ~0.008" to 0.010". It is small enough that I can't accurately measure it with the tools that I have.

I think that I am close to being able to work with medium sized surface mount components. I think that I need to be able to cut an isolation trace of about 0.008" and I think that I am in the ballpark. (I have some more bits on order too that might be a little narrower.)

Overall I am extremely happy. I am starting to get good response & correlation between Eagle, PCBGCode ULP, LinuxCNC, and my milled circuit boards. --I like using the mini CNC mill so much that I would like to get something bigger for working with metal, wood, and plastic projects.

The time this afternoon was very rewarding and well spent. I am ready to tackle some homebrew projects!

73 de NG0R

Saturdays are CNC setup days (part 2)

Do you remember when I said that an 0.2mm end mill was going to be fragile?

iPhone pic of 0.2mm end mils

I had my feed rate set to about 3 inches per minute with about 10,000rpm of bit speed. (I normally use 5-8 inches per minute for the 0.2mm 60 degree vbits as a comparison.)  

It made one isolation cut and then snapped off.  The cut (while it lasted) was ubber small and would be great for SMT work.  <sigh>

Dinner is almost ready so that will put a temporary stop to my work. Maybe after dinner I will try a 0.2mm 30 degree vbit.

73 de NG0R

Saturdays are CNC setup days

I am working on another CNC PCB milling test. I have a bunch of different sized vbits and and "end mill" that I want to check the cutting size with.  I opened up an Eagle file that I was using a couple of weeks ago and made a copy of it so that I can do some experimenting.

Eagle on a Mac

I have new version of the Eagle PCBGcode ULP (v3.6.0.1) that I am trying out. There is always a little bit of tweaking with each new bit until I have the sizes figured out.

I then export the GCode (Mac) and then open it up in another tool called PCBGCode-Wizard. The tool is Windows based so I am running on a XP virtual machine on my Mac. (It will run in Wine on Ubuntu as well.)   The Wizard lets me see the cutting tool path, remove unneeded paths, and optimize the tool movements to reduce wasted movement. In this case I am removing the extra pass that separates the the groundplane since it is not a important for this particular test.

PCBGCode Wizard running in an XP virtual machine

I am going to go test a 0.2mm end mill to see how wide the isolation cut is. I will also get a feel for how fragile this bit is and how fast/slow the table movements need to.

The outlines are actually the path that the cutting tool will take. I have trace widths from 0.001" to 0.025" with each 0.005" increment a little longer so that it is easily to see the steps visually.

The shop is warmed up (it is winter time here in Minnesota) and the Ubuntu PC for the CNC is ready to go. Time to head to the shop (aka: attached garage.)

73 de NG0R

The rig is on

I am doing some electrical design work in the shack this morning and turned on the KX3.

A quick post from my phone.

73 de NG0R

Christmas Eve Skiing

While visiting my father in northern Minnesota we slipped out for a little while. Ben (12) and I headed over to Grand Rapids for some cross country skiing near the High School.

Nicely groomed trails.

Lots of snow on the branches. It is actually a week old but still looks fresh.

Ben (12) out skiing for the second time. He did a good job and was able to manage all of the hills.

Me (40) out skiing for the second time since I was in high school.

Did I mention that it was 0F when we went out? Getting out of the truck and getting dressed outside made me really question what I was thinking about. The reality is that once we were moving for 5 minutes we were totally overdressed. We kind of knew that was going to be the case but it was so cold we errored on the side of caution.  Our excursion covered a little over a mile of trail and was very enjoyable.

I plan on taking the cross country skiis and snow shoes to Iowa later in the week since they have 12-18 inches of fresh snow down there.

CNC milling video from Sunday

Sunday CNC projects - continued

I modified my layout in Eagle a bit from the early posting. I decided to drop the copper groundplane to keep the routing on this pretty simple. The blue vertical lines are traces starting with 1mil on the left and ending with 25mil on the right.

 

I then setup the PCBGCode ULP for wizard to export my board.

I am using a 0.2mm 60 degree vbit that cuts an isolation trace about 12mil wide at 4-5mil deep.

Export script uses 50% of "Etching Tool Size" + the "Default" isolation width to position the cutting bit around the trace. (I found that info on a Google search and it seems to work properly based upon that.)   

I think that my smallest trace on this test run was about 2mill. (The left most and right most trace did not appear in my export and I did not count how many traces until after I was milling. --go figure. )

--Click on any of the images to open the larger versions--

I did a test run yesterday and I was able to drive 1-2mil traces too. This seems like the runout on the tooling is pretty decent assuming that I run a test with each tool and document the configuration for future reference.

At this point I could mill through-hole, 1206 SMD, and SOIC components and probably 805 SMD components with the 0.2mm 60 degree vbit. Anything smaller than that and I will need a smaller bit. (The smaller bits for testing are on order and should be here in a few days.)

Based upon this I probably need to adjust my DRC (Design rule checker) too support 12mil isolation spacing until I can further refine my system which seems pretty workable.

I also shot some video of the project today. I plan to edit that together and post it when time permits.

73 de NG0R

Sunday CNC projects

I am doing a little work in Eagle to validate my CNC setup with a 60 degree 0.2mm vbit.  I have laid out a series of traces and then incremented the trace size.  The traces are 50mil (0.050") on center. The left most trace is 1mil (0.001") and they increment to 25mil (0.025") on the right. The bottom trace on the horizontal axis is a 30mil (0.030") trace.

I am going to see how accurately I can reproduce this test. I expect my isolation cuts to be about 12mil (0.012") with my 60 degree 0.2mm vbit. My expectation is that any of the electrical traces smaller than ~10mil (0.010") are going to be wispy and unreliable with my CNC and cutting bits.

If this test works I will use it to test the new bits that are on order and should arrive this week with some luck. Once I have all of this testing complete I will build a reference document for these tools. That should mean that I can work on single sided prototype boards. --Dual sided boards are research project for another day. ;-)

The garage is heated up so I am headed out there in a few minutes to fire up the CNC mill.

73 de NG0R

Saturdays are for CNC calibration

I found an interesting script for Eagle that can be used to help calibrate your CNC PCB milling settings: 
http://phk.freebsd.dk/CncPcb/calibrate.html

I exported some GCode to go run on the mill.   --I am running Eagle/PCBGCode on a Mac, PCB-GCode-Wizard (when needed) on an XP VM, and then LinuxCNC on Ubuntu.

 I spent a few hours moving between the office and shop this afternoon tweaking Eagle/PCBGcode.ulp and my mill.  I learned a few things so I will consider the Saturday afternoon a success. 

It appears that a 0.2mm 60 degree vbit will cut an isolation trace about 12mil or 0.012" wide. This is pretty consistent with the best of the tests that I ran a week or two ago.   With a SHARP bit I was able to leave behind a 1mil or 0.001" electrical trace. (Yeah, that surprised me too.)  I have pattern of traces from 1-25mil that I used for the test scenarios. 

Gotchya #1: It requires an ubber sharp bit.  Asthe bit wears down or dulls that is a largely unachievable result. The reality is that I would not dare working smaller than 10-15mil electrical traces.  20mil will probably be my norm.

 

Gotchya #2: With the 0.2mm 60 degree vbit my minimum isolation is ~12mil. This going to limit my SMD parts as long as I use that mill bit.

I have the following bits on order:

45 degree - 0.2mm

30 degree - 0.2mm

20 degree - 0.1mm (probably too fragile to use)

End mill - 0.2mm

FYI...

0.3mm = 11.8mil

0.2mm = 7.87mil

0.1mm = 3.9mil

Reality #1: My guess is that ~10mil of isolation might be my realistic limit.  I should have the next round of mill bits here (with luck) by the end of this coming week.  I will need to do some research on SMD package sizes to see how that matches my isolation realities.

 

Reality#2: For homebrew work this is probably will probably more than cover my needs for a while.  Currently I am not working in the crazy small SMD components very often so it is probably not a major limitation. If I need something crazy small it would probably make more sense to send the board out to a fab house or to get an adapter board for prototyping work.

 

Next steps: Document my updated settings so that I can reproduce the results again in the future. Once the new bits are tested my next major testing task will be pin registration so that I can flip the board and mill both sides. Being able to prototype 2 sided boards would let me utilize auto-routers much more effectively and to have more control over board layout and size. 

 

Here is a great link:
http://atxhackerspace.org/wiki/PCB_Engraving_101

That site has some create info that closely aligns with my experiences during my initial testing cycles.

73 de NG0R

CNC pcb milling day 3

Tonight was pretty successful. I spent some time documenting the mill, Eagle, and PCBGCode ULP setup so that I can try to get some reproducible results moving forward. I then spent some time trying to figure out the magic measurement on the Z axis for my 60 degree V bit.  Z -0.0080 is the magic cutting depth for me. (I probably need to slow my feed rate a little bit too.)

Sorry for the camera-phone picture but it is sufficent for 10:30pm on a Wednesday night.  :-)

I believe that I am now at the point where I can start making CNC milled circuit boards for my projects.

73 de NG0R