[ztstone]

Background:
A colleague and I are starting a shop. We are both engineers and would like to offer the ability to make and modify part to our clients. I have a certificate in machine to technologies and worked as a machinist for a short period after graduating. I learned g code programming in school but have not used it in about 8 years.

What we are looking for:
We currently have a manual Bridgeport mill and a Harrison AA lathe. We would like to add the ability to make more complex parts plus all the other conveniences of a CNC. We are mainly working in the 300 series SSs and aluminum. Most of our parts are 6 inch square or smaller and less than an inches thick, but there are occasionally larger parts (mostly aluminum).
I do not want a bench top hobby mill like a sherline or something like that. I was thinking a used CNC Knee mill. I would like to get a vertical machining center with a tool changer, but simpler would be good for now. I have never bought used equipment before. The mill and lathe we have were purchased from a company that I worked for, so I was very familiar with these machines. Our budget is about $10000 (with a little wiggle room) but we need to keep some money for tooling. We are in the San Diego, CA.

Questions:
Is a CNC knee mill a good choice? If not any do you have any other suggestions?

What are we sacrificing if we go for a knee mill?

We would like to use CAM Software to generate some of the programs, are there any features that we need to look for in the controller so we can have compatibility with CAM?

How can you tell if a CNC machine is in good shape? With a manual mill you can turn the handles and feel tight spots and check for back lash. How can you tell what shape the machine is in, if it is computer controlled and has no handles?

Thanks in advance
Ztstone

[austin.mn]

i was able to pick up an older bridgeport boss with blown controls quite reasonable, then gutted the box added some compumotor drives that I purchased off of ebay. The mill runs great, not overly fast, but for the money that I have invested in it I couldn't have done better. As I understand it they are quite a common machine to find in the shape mine was in (great shape with bad electronics). people don't generally do anything with them once the controls start to go out because new replacement boards are quite expensive. So if you are comfortable with rewiring it, this may be a good option to go for you. It shouldn't be to tough to find a machine in your area.

[bglad]

I used a cnc knee mill for about 4 years. If you make cuts that cause much vibration, you can loose your tram, more so cutting the stainless. Then you have to spend time re-indicating your setup. If you have to hold tight tolerances, this could be a major problem. Rigid head is the way to go.
If you find a machine you like, insist on running a test program on a few pieces of the same part, then carefully inspect all pieces for variance.
I have read on this site that the Tormach cnc mill is a popular item, in your budget, and has a fair sized working area.

[ckm]

With much the same intentions as you, but for a totally different output, I bought a Dyna Mechatronics 4400C mill, which is actually a CNC bed-style (not knee) machine (see my sig for more info). I paid $1200 for it, but it needed a near total retrofit to bring it up to current standards, which is going to cost around $2500 total and would take around 3 weeks if I could do it full-time.

I did a lot of research before I found this machine and everything was either way to expensive (capabilities vs cost, mostly) or really crappy. I did find that Brother VMCs are seemingly pretty good value in a small in footprint. I have seen them for around your budget or less, they don't seem to be all that popular. They are often described as 'tapping centers', but some of them came with Fanuc controls and are in fact small VMCs. A friend of mine has one and he just loves it.

Sharp also makes a couple of small VMCs that seem to sell for cheap-ish. I also recently saw some really nice, relatively cheap Taiwanese mills from Akira Seiki (http://www.akira-seiki.com/). Their small VMC is $35k new. And I really would not discount some of the higher end benchtop machines from Industrial Hobbies or Tormach, for example.

I think that part of the choice of mill may depend on your ability and willingness to maintain it. For example, Hitachi-Seikis are really cheap right now (relatively speaking) because the company went bust, but parts might not be that easy to come by.

One thing I would suggest is that if you are doing complex parts that are going to be on the mill for a while, you really, really want an enclosure and probably coolant. Also, if you don't already have it, you can easily spend $20k on software alone. A decent CAM package will cost you anywhere from $1k to $10k and CAD is no cheaper. There are two very good cheaper CAD/CAM packages, Alibre and DeskProto, which can help keep the costs sane.

Another thing to be aware of is that your are in sort of a dead zone for CNC machines. Decent used CNCs will sell for closer to $20k unless they are really beat (and if they are you will spend a fortune fixing them) and 'benchtop'-type mills (like the Tormach) can't match the performance of a real VMC. There are a few options out there, but they all require you making an investment of time and/or money (like the 4400C, which is close to what your are looking for).

Then again, with the economy crashing, you may be able to find something really good from a going-out-of-business firesale, although you'll be competing with people buying for Asian end-users... Keep in mind that I am also not a professional machinist, so I could be totally wrong. Just relating what I have found in the sub-$10k market.

HTH,

Chris.

[ztstone]

Thanks for the advice. I'm looking into the Tormach machine. It looks really interesting.

Z