Saturday, June 26, 2010

PCB isolation routing - attempt 2

Much better results this time. Milled-and-drilled with excellent results. I decided to switch from my 1/4" router to a Dremel tool - this required a new mounting bracket. Naturally, I used the router table to make the new parts. The process is starting to get easier. I routed two brackets from 3/4" MDF and glued together.

I carefully added the mounting holes so I can easily switch from the router mount to the Dremel mount with only 4 bolts. Works great. Another benefit is the Dremel is considerably less noisy than the router, and the Dremel runs cool the whole time. Running a homeowner-quality router for an hour gets scary - you can smell the varnish on the motor windings getting hot.

Added a saw kerf and a bolt to "pinch" the Dremel into place. Like a rock.

Here's the Dremel mounted.

I secured special 1/8" milling bits from DrewTronics. It was the 1/8" shaft that made the Dremel the easy choice. I ordered 30, 45 and 60 degree bits with the idea to play with them all over time. I had to throw 'em under the microscope - here is a 45 degree bit at 20x magnification.

Routing went perfectly. Tooling still a bit to deep. Milling time was shortened considerably by using the gcode optimizer.

After routing, I decided to try drilling too. Snapped the first bit after drilling the 4th hole. Checking the setting of the gcode converter - I found one setting at zero inches - this caused the tool to move to the "home" position for a tool change, but didn't lift the drill out of the PCB first! Changed the number to one inch, and it worked fine, returned the router to the 0,0 position, raised an inch for easy drill changes.

Drill bits are from Jameco and seemed to do an excellent job.

Here's some of the traces at 20x magnification. I did nothing but scrub the board a little with a Scotch scrubbing sponge - no abrasives, no sanding. Was able to get a trace between two 0.100 inch IC pads.

Next I'll ring it with a volt meter, and if all is good, actually build the circuit.

Wednesday, June 23, 2010

Gcode optimization

I tried the Opti - PCB-Gcode Optimizer from JayC. Tried it on Ubuntu under Wine (Windows emulation), it opened, but wouldn't do the optimization. Had to resort to MS-Windows to run the optimizer. Seemed a bit finicky, but once it ran - WOW what a difference. To the right is how the gcode looks coming straight off the Eagle CADsoft program. Click the image to zoom. All those grey-green lines are where the router is moving in between milling actions. The damn thing spends 60% or more of it's time just moving the router from point A to point B.

Enter the optimizer. DAMN! I'd say 95% of the wasted movement is just GONE! This should have an amazing impact on the overall time to mill.

Now if I only knew enough about C++, I could probably re-compile onto Ubuntu!

I ordered some PC milling bits (30, 45 and 60 degree) from Drewtronics. I should have them in a few days. My router is a 1/4" shank, and these itty-bitty PCB router bits are 1/8" shank. I'll need to track down a reducer.

Monday, June 21, 2010

PCB isolation routing with a real PC board

I did not have the proper milling tool. I had a pointy router bit (60 degree) that is supposed to be used for engraving wood. Fiberglass and copper was too much. Nevertheless, the results were very promising. The router bit was more like a snow blower, just heaping the copper up on each side of the trench it dug.

Here is a close-up of the IC pads. It's tough to see, but it is pretty much a mess. I went at it with some 220 grit sandpaper to get rid of the bulk of the nasty high spots so I can get a peek at what was underneath.

To the right is a 20x image of some of the pads for a .100" header - after sanding. I pulled the board off the router before the pads on the right were finished. I also think I had the bit digging-in a bit too deep.

At the left is a 40x image of one of the IC Pads. In both images, even after sanding, the "piling up" of the copper around the edges of the trench is clear.

Couple of early learnings: The cool dust brushes I made obscure the PCB. This isn't a problem for routing, but it makes setting up the tooling a real nightmare. I've got to re-design the brushes such that they are either fully or partially removable.

Second, the CADsoft to gcode converter does an excellent job, technically, but the resulting gcode is very far from being optimized. I'd estimate 40 - 60% of the time to route the board is the router moving from one end of the board to the other. More than half the milling time is just plain wasted.

Next Steps: Order some real router bits. Consider using a dremel tool rather than a wood router. Try to make a gcode optimizer that I found work.

Saturday, June 19, 2010

PCB isolation routing - first attempt

Last night I downloaded CADsoft Eagle schematic drawing and PCB design software. Learned just enough to make a basic board. Used an Eagle to Gcode converter and created the gcode.

Tie-wrapped a rollerball pen in place of my router, added a flat (MDF) auxiliary table on the Router base, got the paper flat.

Started the EMC software, opened the gcode file. It looked perfect with a "rats nest" of jogs. I set X and Y to home, set the touchoff, and hit 'go'. Board is about 2.5 by 2.0 inches.

Son-uv-a-gun. It did pretty damn good. I am pretty sure I had some of the feed rates too high, and I think I skipped a step or two. Nevertheless, I was blown away. It takes a L O N G time to route. One key learning: keep as much copper on the PCB as you can!

Here is a close-of the bottom left of the PCB. The holes are marked quite well in the pad centers. This was not the case everywhere, though. Next time, I will slow down the steppers.

This will make prototyping PCBs fun, clean and fast (faster than the chemical options!).

I will document my complete setup and experience.

Here is a 73 second video of the CNC machine drawing with the roller-ball pen. You can see the pen flex and the paper move - these are, no doubt, large contributors to the inaccuracy.

Wednesday, June 16, 2010

Software - Introduction

The Software. Now this is where things get confusing for me. CAD this and CAM that. I have successfully milled some parts, but I've not yet figured out all the bits.

For the CAD software, I stick with Google Sketchup. Sketchup is a really amazing product. First, it's free. It is 'easy' to learn (for a 2D CAD package, anyway). There are a lot of great tutorials available. I used Sketchup to create all the CAD drawings for building the router, and all the drawings I posted to this blog. Since it's free, you can get your feet wet while preserving some cash.

For the CAM software, I am playing with the demo (40 uses) version of CamBam. The CamBam website says it best: "CamBam is an application to create CAM files (gcode) from CAD source files or its own internal geometry editor".

There is also a free add-in for Google Sketchup that will cleanly export a Sketchup drawing into a format ready for CamBam.

Take some time to read the three-part software tutorial by Patrick Hood-Daniel on his website.

There is a lot to learn about the CAM software, and I'm only just starting. I've found the CamBam documentation to be very weak, almost useless. I did most of my learning by trial-and-error.

For the machining software, I am using EMC (Enhanced Machine Controller). From the EMC site: "EMC2 is software that runs on Linux, on most standard PCs, that can interpret G-code and run a CNC machine." In my case, I use Ubuntu. I had an extra PC, the EMC software installed and ran first time, no problems. EMC plays perfectly with the HobbyCNC stepper driver board.

On a side note: If you have not considered a Linux system, Ubuntu 10.0.4 is amazing. It is quite Mac-looking, fast-as-hell, robust and stable (my server ran for well over a year with zero issues). And with a product called Wine, you can run most windows applications. It's pretty sweet.

I do suggest you use a separate computer to drive your router. It will suck in dust and crap like you won't believe, and you'd hate to trash your home PC. I open my PC regularly and blow out the collected dust and debris. One challenge, is finding a PC with a parallel port, which is required for the HobbyCNC stepper controller. Most new laptops don't have a parallel port. My Ubuntu system had no issue accepting a parallel port card, tho I do remember having a challenge finding some I/O port address or other. But once I figured that out, all was well.

I hope to give some tutorials or other helpful guidance on getting these three products playing together nicely, but time is a rare commodity at the moment.

Dust Control - making the brush

I settled on the idea of a 'brush' or at least 'bristles' for my dust curtain. I couldn't find anything ready made, so I made my own. Works pretty good, and I'm confident when I upgrade to dual 2" vacuum lines, it'll be smokin'. I started by taking pliers and tearing out the tufts from a Harbor Freight workbench brush.

Try to carefully yet securely grab the entire 'tuft' of bristles with the pliers and rock the pliers to pull out the 'tuft'. Some will get messed-up. Keep going. It takes a hell-uv-a-lotta bristle tufts.

The Harbor Freight brush had a neat little staple like gizmo around the 'tuft' of bristles. This came in very handy when inserting the tufts into my motor mount.

I tried drill bits in the holes left in the brush to determine the proper hole size.

I flipped the motor mount upside down and put holes around the perimeter of the router in a highly un-precise fashion - just guesstimating the spacing.

Then I took a small nail set, and with a file, put a very slight "V" in the end. I would open the bristle bunch a bit, line the "V" of the nail punch over the small metal staple, align it with one of the holes I just drilled and smacked it with a hammer. Repeat until you start talking to yourself.

To the left is a close-up of the bristles in the motor mount. It actually worked quite well, and the bristles are held in quite firmly.

I didn't count 'em, but it took a lot of the little buggers to circle the router and dust port.