Has anyone tried to CNC mill boards?

[afischer82]

http://www.engadget.com/2006/06/29/how-to-build-your-own-cnc-machine-part-1/
http://www.engadget.com/2006/07/04/how-to-build-your-own-cnc-machine-part-2/

I found the above how-to for building your own CNC machine using a cheap cutting board, old printer parts, and a dremel tool, and thought this could be a cool alternative to etching boards the traditional way.  I also see some serious potential for tooling and engraving enclosures.  Has anyone ever tried anything like this?  Or, does anyone have any experience with CNC milling that might know some of the pitfalls of doing it this way?

Still haven't convinced my wife that getting a laser printer is a good idea, so I'm still buying my boards from GGG and Tonepad

[afischer82]

Apparently there's a part 3 to that tutorial...
http://www.engadget.com/2006/07/11/how-to-build-your-own-cnc-machine-part-3/

[The Tone God]

Milling boards has good and bad points. The major good points is that you don't need chemicals and you get very consistent results. The bad is you need to know how to program the mill and depending on how complex the board is it may take a long time to mill the board.

As for the design in that article while cheap and cool it takes alot of time to build, uses some weird parts, you need some above average fabrication skills and experience, and you can't be sure of it's tolerances and accuracy.

Andrew

[tommy.genes]

The link to Sherline was pretty interesting. Their "ultimate" CNC milling and lathe package was only about $5k. I had though that CNC milling of boards was a minimum $20k investment.

Not that I'm running out to buy one today, mind you, but it is a tidbit of info to keep in the back of the mind.

-- T. G. --

[R.G.]

I've come up with an incredibly simple way to do CNC boards, and to engrave faceplates and enclosures. It's done with just a batch of old printer parts, and requires almost no mechanical ability.

1. Take a laser printer. It can be any brand or age, as long as it prints a decent image. Even if you buy one new, it costs only about $100-$200. Probably you have one or can use one for free.
2. Get a packet of printable sticky-labels at an office supply store. Remove all the labels and throw them away. Save the backing sheets.
3. Print your PCB pattern or engraving pattern in reverse on the sticky label backing sheets.
4. Clean off the PCB stock or enclosure well and iron on the pattern. Irons are usually already available, but are under $10 if you have to buy one new.
5. Etch the article in etchant. FeCl is widely available and inexpensive, if a bit messy. Cost under $5, and will do many boards.

So if you have to buy everything except a laser printer new, it costs under $50. If you have to buy a laser printer to do this, it might cost as much as $250.

But I do understand the attraction to a $1K+ machine that makes a lot of noise and hazardous dust, requires special milling bits that you break, takes special programming and needs constant mechanical maintenance.

How do I know these things?

[afischer82]

Yeah... the question was more geared towards the DIY CNC mill.  I'm less addicted to pedals, and more addicted to building stuff

The DIY CNC mill looks like it could be done for pretty cheap since I already have a dremel with a flex shaft.  All I would need is the cutting board, stepper motors, rails, etc., most of which appears to be pretty inexpensive.  So I was more wondering why I shouldn't do it. 

That being said, I didn't realize you could do iron-on transfer with the backing for labels.  Do you print on the slick side?  That's gotta be cheaper than press'n'peel blue. 

[puretube]

R.G.: you forgot drilling the holes... 

[R.G.]

you forgot drilling the holes...

I absolutely did. I can get a benchtop drill press suitable for drilling PCB holes for $39.00 locally. If I want to do a GREAT job, I can buy a jeweler's drill press for about $150.00 (I did...)

Yeah... the question was more geared towards the DIY CNC mill.  I'm less addicted to pedals, and more addicted to building stuff

That's a different story altogether! If making stuff in general is your addiction, by all means. I put together a 2' by 3' CNC 'Christmas Machine' with a couple of friends. We used an air powered die grinder with an end mill mounted in it for the cutting tool. Worked great - but it was a LOT of work to keep it running.

The simple small CNC machines are fun, and since the linear bearings and alignment isn't nearly as critical as in the bigger machines, they're less work. But they are expensive, even at DIY rates. A lot of the mechanics can be DIY'ed too. I have a lathe and milling machine out in the shop, so this is another of my several addictions.

In fact, a good start at a CNC mill would be to buy Harbor Freight's micro mill-drill or their mini mill-drill. The micro mill-drill costs $300 when it's not on sale, and will mill anything inside a 9"x4"x8.5" volume without recentering the work. It's basic accuracy WOULD allow you to do a good job of repeatably drilling PCB holes, and the work to make it CNC consists of adapting motors to the handwheels that are already there. The programming and interfacing are the same.

The mini mill is $470.00 when it's not on sale, and offers a much bigger machining volume. Both of these machines will do the work to make the parts to convert them to CNC, by the way. And they are frequently on sale for as much as 20% off these prices.

I am in the process of trading up to one of these: http://www.grizzly.com/products/G0463. 

And you think you have an addiction... 

[puretube]

freehand-drilled 1280 holes of 0.6mm each in a 10cm x 16cm PCB lately...
faster positioning than with a drill-press. 

[R.G.]

Back when I was selling PCBs, I was doing about 2K holes in a 15cm x 30 cm panel - does that count?

It took me about 90 minutes with jeweler's drill press, and I had to pay attention. I set up a fixed magnifier-lamp to see the targets better and had a vacuum cleaner exhaust hose blowing away the cuttings so I could see the next hole location better.

I'm sure that a CNC rig would be better. Might cost more, too. Isn't it always the case that life is a series of trade-offs? 

As I mentioned, I have some experience with doing home-built CNC. It's a great thing, but it does require a lot of time and money invested up front to get started.

For an 0.062" (1.575mm) pad in a PCB, you need to put the hole on target with no more than a 0.010" (.254mm) error on each hole, which means that your basic centering error has to be (a) modestly good to start with and (b) guaranteed to be non-accumulating.  An accumulating error of 0.001" (0.0254mm) per cm will walk you out of alignment with the PCB tracks on very small boards. There are lots of these little issues to be resolved.

CNC is a fun arena, but demanding of both time and money.

[davebungo]

I don't know if anyone else has mentioned this technique before for drilling your own PCBs:
If you can keep all holes on a 0.1" matrix in your PCB artwork/design (which will of course be the case for IC's), then you can stick a paper template to the top side of a piece of vero-board and then in turn onto the PCB.  It helps if you use/create some "datum" holes in the PCB artwork to line the PCB up with the vero-board (I use PCB pins to hold the PCB and Vero together).  You then simply drill through the paper template, through the hole in the vero-board and through the PCB.  The vero-board guides the drill very accurately.  It has worked well for me.  I used a small drill press but it could work free-hand as well.

This obviously only pays dividends if there are quite a lot of holes to drill.  It probably isn't worth it for a simple circuit board.

...and you waste a sheet of vero-board since the holes do get a bit damaged by the slight wandering of your drill.