First-timer: Machine for PCB Milling (Primarily)

[sansbury]

Hi all, I am looking for recommendations for a first-time machine builder.

Purpose: My foremost interest is PCB milling and drilling for boards up to 4"x6" or so in size, using ordinary thru-hole construction. Most of my work has been in audio applications where you're not dealing with crazy-small SMT pads and traces, though I wouldn't object to improved accuracy if it can be obtained.

Secondarily I'm interested in ability to do limited work in acrylic or high-density foam for prototyping things like knobs, small panels/plates, that sort of thing. If I can work in aluminum I'd be very happy but I don't expect it.

Skills and capabilities: I'm a software developer by trade and (very) amateur electronics hobbyist, so I feel reasonably comfortable in my ability to piece the electrical bits together. Mechanically I am competent in wood, while my father has a very good shop and can help doing high precision work. I also have a friend who owns a commercial machine shop with (I think) 5-axis CNC, laser cutters, etc. I don't have free run of the place and it's 100mi from where I live, but if I need one or a few parts done, it's not a showstopper.

Budget: Would prefer to keep it as low as possible. Knowing that most DIY projects end up costing twice as much as I start out thinking they will cost, I'd like to target $200-$300. I have a good spare Dremel and lots of ATX PSUs laying around, but I'd prefer something that did not require too much scrounging to meet a budget as I prefer to spend my time building and not shopping.

I would also prefer something that is a common design with a good number of builds, though I'm OK working from plans only if they're decent quality. So far the Brute II on the Crank Organ site seems the closest match, though I've also been looking at the Joe2006 for comparison.

[epineh]

Joe's machine is good by all reports, also look at the JGRO machine (its here somewhere), little smaller and will do all you have mentioned, except aluminium ( I think).

My machine (own design) is accurate to 0.01mm, though I wouldn't use it for the smaller SMT parts, but I milled quite a few boards very successfully, just standard stuff, if you can follow a plan, the JGRO is built with mainly MDF so this will keep costs down.

Not too sure if you will come in under $300.00 though.

Good luck

Russell.

[pminmo]

The biggest issue with milling pcb's is "tightness". Cheap threaded rod will give you enough accuracy. My experience is 2mil's backlash is difficult to live with. Make a machine that is no larger than you need.

[ringram2077]

Look at the Rockcliff design. It is the right size (12X12 cutting area) for what you want to do and it is easy to build. Different options if you need more accuracy. I just finished the basic design with bronze bushings and ground rod.

[wizard]

If you are new to this sort of thing then the use of a set of plans is in order. The issue is which set, which unfortunately I can't answer. I simply have no experience with any of them.

The ability to do PCB's well though implies a bit more accuracy then some of the cheaper designs will be capable of. The issue is getting pitches right for the smaller parts, especially if you go out side of the audio realm. Mechanically there is not a lot of reaction forces to deal with from the tooling so modest machines can be effective here.

The problem comes in when you mentioned some of the other things you would like to accomplish. Milling thin aluminum common to electronics enclosures really isn't a huge problem either. It takes slightly more effort from the machine. The biggest problem is effective clamping of the sheet stock. Where I see an issue though is with the machining of knobs and other larger pieces.

The problems with the larger pieces is that reaction forces are larger thus requiring a stronger machine or lots of small passes. Either way repeatability and rigidity are more important especially if you are wanting good looking parts. combine that with the potential need for different spindle speeds and you wind up needing more of a machine then if you where just doing PCB's and sheet stock.

Now that is not to say that One machine can't do it all (at least all you mention) just that you may want to pay attention to how the machine is designed and its rigidity. If you are serious about milling parts like knobs and other components that are built out of things other than sheet stock I'd suggest making your mill out of metal. Having access to a machine shop should make this much easier for you then many of us here. A very reasonable alternative is to buy a mini mill and do a CNC conversion.

The economics of a CNC conversion might push you to a mini mill. The nice thing with this approach is that you end up will a machine that is a bit stiffer for the machining of larger stock. The machine can still be used for PCB work and many are of ideal size for this. There may be a need for a nigh speed spindle but that is a given and it is not unheard of to have a dremel bolted to a mills headstock for such work. I offer up the idea of a conversion because it would seem to fit your needs and would be quick. You would still end up needing access to a machine shop but the amount of works is vastly reduced.

The only problem I can see here is if you want or desire to handle 19" panels. Then you are talking about a larger mill, tricky setups, or back to a router design. The router ends up getting real big real fast. The way I understand it you are looking for desktop hardware.


dave