Need PCB Milling Settings

scott216
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Need PCB Milling Settings

Post by scott216 » Sat Apr 26, 2014 5:20 pm

I've got a stock shapeoko 2 and I'm going to try to mill my first PCB. I'll be mounting my PCB with double stick tape on a piece of MDF which I leveled with the shapeoko. I've got 10 degree V-bits (like these) and singled sided PCB from Inventables. I plan on using PCB-GCode to generate the gcode from an Eagle file. For starters I don't need really fine pitch or thin traces. Since I've got stock Shapeoko 2, my max spindle speed is 30k; I think I read somewhere that PCB milling likes it much higher, but it it what it is. I'd like some advice on what feed-rate and depth setting I should start out with (and any other setting in PCB-GCode that would be important). I've read that this seems to be somewhat of a trial and error process, but I'm not sure where to start with the settings.
Shapeoko v2 with DW660
GRBL v0.9i
Location: New Jersey

WillAdams
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Re: Need PCB Milling Settings

Post by WillAdams » Sat Apr 26, 2014 6:20 pm

What we have thus far is here: http://www.shapeoko.com/wiki/index.php/Materials#PCB

I'd really like to get more data for the SO2....
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

scott216
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Joined: Thu Oct 10, 2013 12:35 pm
Location: New Jersey

Re: Need PCB Milling Settings

Post by scott216 » Sat Apr 26, 2014 8:02 pm

WillAdams wrote:What we have thus far is here: http://www.shapeoko.com/wiki/index.php/Materials#PCB

I'd really like to get more data for the SO2....
Not really anything here yet. I did one little test, but it turns out the run-out in my Dremel is too high. I have a 2nd Dremel and it has high run-out also. I've got a Dewalt DW660 I'm going to install, but I need to make some brackets first. I checked the runout on the dewalt and it's about 0.002"

My test was at 0.005" deep at 2.5 IPM Feedrate. In MakerCAM I made a 2 x .02" rectangle and did a profile cut. I wanted to make the tool diameter 0.0018 inch, but MakerCAM doesn't seem to support anything less then 0.004 inch. For a 10 degree taper bit, I calculated the effective diameter to be 0.0018 inches at 0.005" depth.
If anyone's interested, in Excel this is:
=TAN(RADIANS(B3)) * B4 * 2
Where B3 is the angle in degrees and B4 is the depth in inches
Shapeoko v2 with DW660
GRBL v0.9i
Location: New Jersey

scott216
Posts: 228
Joined: Thu Oct 10, 2013 12:35 pm
Location: New Jersey

Re: Need PCB Milling Settings

Post by scott216 » Sat May 03, 2014 4:31 am

I did my first PCB test cut and it came out pretty good. The only issue seems to be flatness. I used double stick tape and attached a piece of masonite to my table, then milled it flat. Then used double stick tape to attach the PCB. The PCB milled great in the center, but the side were lower and didn't get milled. So I need to figure out what's going on. I guess I know what I'll be doing tomorrow.

I used Cadsoft Eagle with the PCB-Gcode script to create the gcode file. The file it created had a few comments in the beginning that were longer then 50 characters and that generated an error with grbl - easy to fix though.
The settings I used were:
Feedrate 20 IPM
Depth 0.005 inch
Bit Width 0.0025 inch
Spindle speed 30,000 RPM

The bit I used was a 10 degree tungsten bit I got on ebay. I calculated that if my bit is 0.005" deep the effective diameter would be 0.0018 inches. I did some test cuts and it was about 0.016 inches - almost 10x wider then calculated. I guess I've got a little runout in the bit, the chuck or the DeWalt DW660. I did put a dial indicator on the DW660 and it was pretty good - I think it was a couple mills. Maybe I need one of those precision collets. Anyway, the results are pretty good as is. I originally tried using a Dremel, but it had way to much runout. I looked at two different Dremels that I have and the runout bad in both. Other then the DW660, I have a stock ShapeOko 2 setup (for now).

Once I get the setup flat, I'll use 0.016" as the diameter since it seems closer to actual.

I attached a couple pictures so you can see the results. The closeup picture has a ruler with 1/50" graduations.
Attachments
Engraving Bits.JPG
Engraving bits from ebay
Engraving Bits.JPG (33.43 KiB) Viewed 8768 times
PCB Test_closeup_140502.jpg
Closeup with my USB microscope
PCB Test_closeup_140502.jpg (100.67 KiB) Viewed 8768 times
PCB Test_140502.jpg
PCB showing areas not milled
PCB Test_140502.jpg (254.27 KiB) Viewed 8768 times
Shapeoko v2 with DW660
GRBL v0.9i
Location: New Jersey

scott216
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Location: New Jersey

Re: Need PCB Milling Settings

Post by scott216 » Mon May 05, 2014 9:53 pm

I did another test and which didn't work very well. The edges were very rough, but not all the edges were rough. Some looked pretty good. I don't know why. At first my feedrate was 20 IPM, but the tip of my bit broke (using 10 degree engraving bits). So I lowered to 15 IPM. I measured my runout and it's about 0.010". I don't know if that's the problem or not. I had runout on my first test and didn't get all these jagged edges. I'm using DeWalt DW660 with a fixed RPM of 30K.
Attachments
PCB Test 2.jpg
2nd PCB Test - jagged edges
PCB Test 2.jpg (130.67 KiB) Viewed 8724 times
Shapeoko v2 with DW660
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cvoinescu
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Re: Need PCB Milling Settings

Post by cvoinescu » Tue May 06, 2014 12:07 am

Probably the most useful thing you can do at this point is to add auto-levelling, and experiment with the depth of cut. Or, you may want to try a very small stub endmill instead of the engraving bits. Those are more likely to cut cleanly, and they're less dependent on the exact depth.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

scott216
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Location: New Jersey

Re: Need PCB Milling Settings

Post by scott216 » Tue May 06, 2014 1:55 am

cvoinescu wrote:Probably the most useful thing you can do at this point is to add auto-levelling, and experiment with the depth of cut. Or, you may want to try a very small stub endmill instead of the engraving bits. Those are more likely to cut cleanly, and they're less dependent on the exact depth.
Thanks. What diameter endmill do you recommend? The leveling shouldn't be an issue. I had the PCB on a piece of masonite which I milled flat. After attaching the PCB with double stick tape I put a dial indicator in the DeWalt's chuck and moved it over the PCB to check for level and it was very good. I am planning on playing around with the depth setting.
Shapeoko v2 with DW660
GRBL v0.9i
Location: New Jersey

ThinkItShapeIt
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Re: Need PCB Milling Settings

Post by ThinkItShapeIt » Tue May 06, 2014 11:57 pm

I second the recommendation to use an end-mill rather than the engraving bit. I tried cutting a circuit with an engraving bit and didn't have much luck. Overall, an engraving bit requires much more precision in your Z than an end-mill. Without auto-levelling, it may not be possible to get great results unless you find some copper clad with a very very consistent thickness.

My father milled an RN42 bluetooth breakout board the other day. The cuts are very clean with an end-mill so no cleanup is necessary after a job. Here are some pics.

Image

The extra copper clad was manually peeled from the board.

Image

You may want to try slowing down your cuts too. This circuit was cut at 5IPM taking .003" at a time. He used an .0118 two flute end-mill from Drillman (eBay). Even on such a small circuit, two passes were necessary to get through the copper clad across the entire circuit. A single pass would probably be sufficient with auto-levelling but I'm not aware of an auto-levelling setup that works with GRBL.

scott216
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Location: New Jersey

Re: Need PCB Milling Settings

Post by scott216 » Wed May 07, 2014 1:07 am

That bluetooth circuit is really nice. I'm gonna order an end mill and give that a try. I think I'll also get come engraving bits that have a bigger angle, maybe try 60 degree instead of 10. I tried slowing the feed down to 3 IPM and that didn't help. What did help was some WD40. I did a quick test at 10, 15 and 20 IPM. The edges were rough, but after a light sanding they actually came out pretty good. See picture below. The top trace is 10 IPM, middle 15 and bottom 20.
Attachments
PCB Test 3.jpg
Test with WD40 at 1- to 20 IPM
PCB Test 3.jpg (112.28 KiB) Viewed 8655 times
Shapeoko v2 with DW660
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Location: New Jersey

scott216
Posts: 228
Joined: Thu Oct 10, 2013 12:35 pm
Location: New Jersey

Re: Need PCB Milling Settings

Post by scott216 » Fri May 16, 2014 1:07 am

My 0.0118 (0.3mm) end mills arrived and I did a couple tests. It's surprising to me how "non-flat" the PCB board is. It's held is down on a milled surface with double stick tape. A few people have said that tapered bits don't work well if the PCB isn't flat, so I'll probably stick with the end mills for PCBs.

For my test, I just did a couple of straight lines. I used my DW660 (with 0.010" runout). First time I took shallow cuts 0.001" and went down 0.005" in total. This turned out pretty good. The width of copper cut out was about 0.020". Next I tried 0.002" cuts going down a total of 0.006". This turned out okay also. It did need some slight sanding.

Today I got another DW660 because the one I'm using gets very hot so I think the bearing is bad. The first thing I did was grab the new 1/8" collet and check the runout. The runout was much less, only about 0.003" I did another test with my original DW660 with the new collet and the cut came out very nice. It was narrower (I didn't measure it) and the edges were nice and clean. Tomorrow I'll do a real test with PCB design, not just a couple straight lines.

BTW - the new DW660 runs hot also - can't touch the nut. So I'll just send it back.
Shapeoko v2 with DW660
GRBL v0.9i
Location: New Jersey

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