This is one of those wonderful “how long do you have to listen to the answer”-type questions. To get a real, full answer, will take quite a while. But let’s start in on the top-level items, and see how far we can get.
First off, look at your budget. One of the fundamental truths associated with buying any machine tool (mill, lathe, shaper, surface grinder, etc.) is that the associated tooling will cost as much - if not more - than the basic tool itself. So if your full budget is $2500, you need to be looking at mills that are in the $1000-1300 range. So right from the start, you can elminate anything like a brand new Bridgeport or large free-standing model. You are in the range of a benchtop mill/drill, or a benchtop mini-mill, or maybe a used floorstanding machine (if you are willing to put in the time to refurbish it properly).
Once you have the budget identified, look around and buy the largest capacity machine you can afford. If you think you only need a machine with a 8x24" table, but you can afford one with a 10x36" table, always pay the extra price and get the larger one. Fundamental truth number two is “the largest piece of material you have to machine will always be two inches larger than your machine can handle.” A large machine can always work on small parts, but the inverse is not always true. Even if you can’t think of anything on your robot that will need a big capacity machine, you never know what you will want to work on during the off-season or next year.
The next thing to think about is support and maintenance of the machine when you buy it. Is the manufacturer still in business and/or is there a distributor network for spare and replacement parts if you need any? Is the tooling interface a standard size, so tooling will be readily available and inexpensive? Will you have access to other people that have used this make/model machine that you can turn to if you need help? Time for fundamental truth number three: “when your made-in-the-USA machine tools breaks, the part needing replacement is the one piece that was manufactured by a defunct company formerly located in Eastern Slobovia in a factory that now produces shower curtain rings. Your custom-made replacement part will cost more than the original price of the whole machine tool.” Having access to a bunch of other owners of the model XYZ mill will help you find sources for these replacement parts (one great resource is on-line user groups - check Yahoo.com for “model XYZ mill users” or whatever).
OK, so with all that said, here are three specific recommendations:
- Consider the Rong-Fu model 31 mill/drill. It is right in the middle of the price range and capability space that you are looking for. I know of several teams that use this size machine with a lot of success. They use R-8 tooling, which is commonly available. There are several on-line groups (such as the Yahoo Mill-Drill group) that are very active and helpful. And, best yet, Enco has them on sale right now. If you can afford it, go ahead and bump up to the model 45 with a square column - adjustment of the head height is a breeze with this model.
Note: be sure and look for the Rong-Fu model, which is made in Taiwan. They are good quality machines, apparently made by a company that still gives a crap about quality and tolerances. Problem reports on them are infrequent. There are several makes of Chinese knock-off copies, most of which have real problems ranging from sand-filled castings to skewed table ways to horrible backlash problems on all axes. Avoid them like the plague.
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Since you are in the area, get to a meeting of the Chesapeake Area Metalworking Society (CAMS). The CAMS members are active and retired machinists that enjoy metalworking as a hobby. They constantly debate topics like “what is the best mill for my budget?” and can provide a LOT of good information. There is also an active sub-group focused on CAM systems, and converting manual mills to CNC capability (for when you are ready to take that next step).
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Depending on your schedule, there is an event in late spring you may want to consider. At the end of March, there is an annual surplus machine tool sale and auction held in Richmond VA. If you are interested in used machine tools, you can get some great prices here (as good as 10 cents on the dollar against original purchase price). The auction is typically supplied by machine shops that are upgrading or going out of business, and the inventory is always varied. If you go this route, just be sure that you have the ability to evaluate the tools for quality so you don’t get taken and have access to someone skilled that can refurbish used machines.
I hope this helps. Let us know what you decide!
-dave