Trying to go zero to 60 in CNCing

[DigiTan]

Background

I'm starting a long term craftsmanship improvement project. What I do is rapid electronic prototyping and occasional freelancing where I need to mill case openings for keypads, lcd screens, connectors, etc. Some are aluminum, but the real day-to-day stuff is plastic.

Anyway, the routing and milling are the only parts I really dislike. Until a year ago I did it all by hand, but even with a typical dremel routing table the slowness, unevenness, high runout, and mess make it impossible to do anything really high-quality. I know part of that is technique, but after grappling issue this all month, I realized the only real solution is to automate.

Request
Basically [nomedia="http://www.youtube.com/watch?v=U9-mPOA7PXs&feature=related"]YouTube- CNC Mill Front Plate[/nomedia]. The problem is I have little mechanical experience other than small power tools. Actually, I just found out what CNC means this month so you can count me as a rank amateur. After asking around the web and youtube I was sent here to just find a direction to start in.

• If I want to do a first-time CNC mill for plastic and aluminum, is 1mm accuracy realistic?
• Can you give me a run-down of the tooling and skills needed to build that type of CNC?
• Is there a basic construction type I should look at first (gantry, XY table, etc)?
• Which sub-forum should I look for?
• Any other advice?

Hoping for 1mm accuracy | Biggest case size is probably 8"x8"x4" | 1/8th" thickness

[rowbare]

You can easily get accuracy of much less than a mm. I would suggest a cnc'ed Taig mill as a good option. It is reasonably priced and, with a well selected controller/motor package, can be up and running in a couple of hours. The travels are roughly 12x6x6 so it falls a bit short in the Y direction. However you can probably work around that quite easily.

You want to buy one with a Gecko G540 based controller. A couple of dealers who offer those are;

http://www.deepgroove1.com/cncmill.htm
and
soigeneris (you will have to google them)

I bought from deepgroove1 before the G540 came out and have since upgraded to the Gecko. I have ordered parts and accessories from Soigneris and have been pleased with the service. I think Soigeneris' controller is a bit nicer but you pay a bit more.


bob

[DigiTan]

Okay. I'll to shop around just for comparison, but this is exactly the type of thing I'm looking for.

So I'm guessing the DeepGrove model would come pre-assembled, then I'd add the Gecko and Mach 3 program seperately to be up and running?

[rowbare]

The mill itself comes in two boxes. One contains the column and the other the base. The controller and motors come in another box. You have to bolt the column to the mill and align it and you have to attach the motors to the axes and do the hookups etc... It is pretty straightforward. Deepgroove has a couple of videos that show what to do: http://www.deepgroove1.com/videos.htm

bob

[DigiTan]

This is looking pretty good so far. Would this CNC or one very similar to it be capable of milling printed circuitboards as well? The copper traces generally require 1.98mm, 0.790mm, 0.457mm, or 0.350mm of isolation, depending on the parts involved.

[er-mtl]

Hi,

As mentioned by "rowbare", 1mm precision is awful. If you invest in a CNC machine, it's to get quality results, not an automated way to make low quality stuff. On a faceplate, you will probably need to draw some letters that are only twice that size. Precision needs to be at least 20x better (0.05 mm) to get sharp results. Also, backlash on bad home made machines will make any curved shape or machined hole ugly.

If you really don't like milling faceplates and it ends up with a mess as you mention, trying to make the mechanical part of your own CNC machine seems like a recipe for disaster. Buying a commercial frame is the obvious choice.

The TAIG machine above is very capable for aluminum and even mild steel. It would be a good choice if the 5.5''x12'' (140mm * 300mm) XY size is enough for you, but you mentioned 8"x8" size.

Since you plan on doing mostly plastic, longer milling time when you need to do aluminum parts should not be a problem. if that well describes what you want, then a gantry style machine could be better for you and offer much larger workspace.

I have a K2CNC KT2514S-09 that's not as precise as the TAIG (less rigid) but the work area 25''x14'' (635mm * 360mm) is 5.5x bigger and more than enough to do almost all electronic enclosures including 19" rack faceplates (or even complete racks except the sliding rails). If you are sure you will never need more than 14"x14", then the even less expensive KT1414 might be right for you. If your budget is higher, you can go for the KG models that are higher quality and offer better rigidity (ballscrew & supported rails). You can find them all on this page and there is a forum about K2 machines on CNCZone.

it's not advertised on their website, but you can order just the frame (they sometimes sell them on ebay), and prices are much lower than complete machines . 0.2 pitch lead screws are available at the same price and allow for twice the speed while maintaining precision with microstepping controllers. Make sure you get the couplers, cable rails, zero switches, router support, router (I like the Bosch Colt) and T slotted aluminium table top is you want it). Since you're into electronics, adding motors, 48V power supply and a controller should be easy (use shielded cable for the motors !). Keling is a good source for the motors, controller and power supply. I went with KL8060 drivers and KL23H2100-50-4B motors, but that's overkill. 3 x low inductance KL23H2100-35-4B (or even KL23H276-28-4B if your budget is really tight) a Geko G540 and a KL-350-48 48V/7.3A power supply will give you a very responsive machine for less money.

Other things you will need for a complete machine include limit switches and an Emergency stop button. You will also need a shop vac to clean the chips, a strong table (else, depending on the acceleration for your axes, it might get quite jerky !), Calipers (chinese made with inch/mm conversion are very nice and cheap when they go on sale) You can find better ones, digital scales, dial indicators and more here (the "anniversary sale" is just a marketing trick, it's the regular price) or there (they have lots of stuff that might be useful later).

To control the machine, you will need an old or low end PC. I used an Atom based all in one motherboard with 1Gb of RAM (512M is enough) as recommended on the EMC website. The board I used is not sold anymore, but it was similar to this one. A faster processor is not always better. Many motherboards with elaborate power saving features or integrated video card will have latency spikes (really bad !). The CNC control software is either Mach3 (Windows) or EMC (Ubuntu Linux). EMC is free and you can get a bootable CD image that includes both Ubuntu Linux and EMC, all configured, so you'll really be up and running in minutes as it works from the CD and then you can install it to even a tiny hard drive. You don't need to be a Linux guru to use it. If you mainly use Windows or a Mac, this file "teleportation" tool will be very useful as it automatically replicates and updates files across a set of machines, no matter if they are Windows, Linux or Mac (they have a 2Gb free version, and 2Gb of CNC files is more than you need).
To design your faceplates and other stuff, you'll need a CAM software. Here too you can get a basic version of CamBam for free (Windows only). You can also draw 3D objects with Google Sketchup (Windows & Mac), export them to .stl format with this plugin and mill them with Freemill.

You can make PCBs with these machines if you're careful. 0.35mm is 14 mils, that's very realistic and should work fine if the PCB is well clamped. There are some tiny spindles designed for that use (Wolfgang Spindle). You can also use a regular router with precision collet, else the spindle runout will cause vibrations and premature bit breakage. I tried standard/precision collet with my Bosch colt spindle and there IS a difference, even for woodworking.
For finer geometries needed when using small pitch SMD components, X and Y precision are quite easy to achieve but depth (Z axis) is a problem since PCB itself is never perfectly flat and 5% thickness variation across a board is normal. The most appropriate tools are V blades (tiny flat end milling bits are too fragile except for very high end machines). Since with V shaped bits the cut width increases with depth, doing fine lines PCB with constant cut depth will be a challenge. Usually, a floating head (or better, a simulated floating head) is required. There is another interesting principle in this thread that seems to yield impressive results.
PCB software and milling plugin are free.
I bought V shaped milling tools and small routers bits from this ebay vendor from Hong Kong. Delivery time was good.
I have just bought a 100 pcs drill bits set from this guy (USA, not yet received, but fast answers from the vendor are a good sign).
Since you do electronics prototyping, you can also easily use the CNC machine for solder paste deposition (no need for messy stencils), and even basic pick and place and controlled heat gun soldering. all you need for this can be found here (syringes, nozzles, USB microscope, vacuum pickup, heat gun, etc ...).
Being able to control every step of the way turning your CNC into a "desktop factory" when crafting electronic devices will really send your productivity to a whole new level !