Please help: which machine to buy?

[jmpatten]

I run a small business designing new types of user interfaces to computers, and I'm looking to do some rapid prototyping of plastic enclosures for a new product. The PCB that will go inside the enclosure is roughly circular and 1.7 inches in diameter, and whole thing will be about a half inch high.

I've been looking at Sherline mills, Taig mills, Syil, Tormach, IH, various brands of laser cutters and 3d printers, but based on size and cost considerations I've pretty much narrowed it down to the Sherline, Taig, (or other similar sized mill) or just outsourcing this job and getting something nicer later. For me the value of doing this in-house is that I can iterate a lot faster and get to the final design more quickly. Also I would use the mill to produce parts more quickly in the short term, but if the product takes off I'd use the case design as a starting point for an injection molded version.

At school I learned how to use a waterjet, lasercutter, and zcorp 3d printer, but I never got to try the CNC mill or lathe. But I have a feeling that there are a lot of extra steps involved in getting to a working part than what I'm aware of. So, a few questions:

1) Would a Taig CNC mill be suitable for cutting models out of ABS plastic? Would another plastic/mill combination be better? Does milling plastic create fumes or bad smells? Would liquid coolant be required?

2) How does the routine maintenance and number of steps to make a part with one of these machines compare to a laser cutter, or a waterjet? I gather there is a lot of lubrication to be done. How long does this take? Are there other tedious steps in the process that I should know about?

3) I'd like to do my modeling in solid works and then take the part from there to whatever CAM program the mill talks to. Is this easy to do with the desktop mills?

4) A lot of people talk about servos versus steppers and ball screws versus acme screws... Do I need to worry about missing steps when cutting ABS, or is this only an issue with metal? Likewise, can I get away with acme screws with a softer material, or is the material hardness not related to the issue of backlash?

5) If one buys a CNC desktop mill, like the Taig or the Microproto one, how long does it take in terms of setup before one can actually make parts?

6) Is there anyone in or near Cambridge, Ma who would be willing to show me a desktop mill in action?

SOrry for asking so many questions! Thanks in advance for any advice!

[Stepper Monkey]

The Taig would serve perfectly for ABS and the level of detail you would need. The Sherline probably would, too, for that matter, but it isn't anywhere near as much of a machine for the money. The Taig is probably the easiest to set up and get running, almost works out of the box. It is limited in size, accuracy, speed, and power for larger items and really serious metal cutting as compared to full-sized benchtop mills like the Syil and the Tormach, but still well within the tolerances I think you are looking for. It also has the advantage of being small and quiet enough you can put it on your desk next to your computer.
If you think you will be using the machine in the future for larger, heavier projects or production work, a Syil X3 or the Tormach would have a lot more capacity and flexibility, but at a higher cost and much steeper weight and space requirements than you probably need just for a small plastic prototyper.
Steppers will work fine, and probably for your needs as well or better than a servo system if you haven't set one up before. Backlash is not related to the material itself, it is inherent in the screw and nut design. I have the feeling that the difference between .0025" vs .001" is probably not relevant for your needs from the sound of it, and the cost and complexity goes up significantly for that difference, so the screw type of any machine you are considering probably shouldn't worry you too much.
In other words, a Taig set up with steppers isn't the best at anything by far - but it is a small, solid, bulletproof, extremely inexpensive, easy to learn and nearly maintenance-free machine that can likely do everything you need it to do very well given your constraints.
If you really do need insane accuracy, rigidity, or cutting at production speeds it isn't your answer, but then you are looking at likely adding a zero to the cost of the rig.
Then I would look into things like a Roland or other small, hyper-accurate machine for small plastic prototype work instead of going to a larger machine.

[Harryman]

The Taig's a great way to start, good value and there are plenty of other users out there to provide help and tips in setting it up.

If you want more accuracy from a small mill, I'd suggest looking at Minitech, they have various models from $5K and up.

I'd say keep it small if you can, no matter what mill you end up with, it's a lot easier to deal with a small mill.

It'll help to keep the plastic cool while cutting, you could use cutting fluid or set up a air jet, easier and less mess.

[jpatten]

Thanks for the replies. Sounds like Taig is the way to go at least to start. I don't need that much precision at the moment. It's also great to know that the Taig doesn't need much maintenance. Even though they are probably overkill for me right now, the work made on the Minitech's looks *amazing* !