affordable CNC with decent tolerances and speed

I would like to CNC vertical mill some 2024-T3 aluminum parts from stock approximately 12"X12"X2". The parts are about 6"X6"x2" and have
a general profile tolerance of +/-.001. The parts will require full 3 axis machining.
What are my basic options for a fairly affordable CNC but one that has decent enough speed and rigidity to make these parts in an average/reasonable amount of time? For instance I would be happy if I could make them in half the time that say a $50,000 used Haas or Fadal VMC could make them in. The machine would only run about 10 hours a week so it doesn't need to be too hell-for-stout.
A small machining center? A retrofit/conversion? A benchtop? Import vs domestic? Other options?
I would like to keep the price down under about $7k if possible. Am I dreaming?
Thanks folks.
Joe
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On 2 Feb 2005 23:05:27 -0800, joe_d snipped-for-privacy@yahoo.com wrote:

+/-.001, 3 axis profiling, <$7k, half the machining time of a machine costing 7x ??? Not gonna happen.
Your main issue is that I don't think you'll find a machine fast enough for +/-.001" on 3 axis in your price range. Your cutting AL, but I also don't think you'll find anything rigid enough in your price range to hold .001".
If you want fast feed, that also means faster spindles. Fast spindles means hotter cutters and you'll want flood coolant and that generally means an enclosure. Enclosure cost more money. So do the pumps, tanks... for the coolant.
You don't want to pay $50k for a machine but want better than that level of performance. Regardless of your opinion on Fadals, Haas' etc, you really *do* get something for your money spent.
Decide which of your parameters you'll sacrifice (tolerance, speed, price).
--
Skuke
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= For instance I would be happy if I

think you mean twice the time
The machine would only run about 10 hours a

Look for bridgeport rigid ram cnc , 7k all day, I prefer heidenhain, but the very late BOSS [with a crt for instance] are ok from what I hear, the the bridgeport factory pc controls seem to get mixed reviews.
get as new as you can afford.
buy nothing prior to about 1985, preferably 1990
if this is a money making proposition, don't be afraid to borrow money, those HAAS toolroom mils start around 20, so a 4 year lease is something in the 4 hundreds a month, do the math.
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Wasn't there a big lawsuit over Bridgeport's home-grown CNC controller? They were using customers for R&D, and a lot of them weren't too happy about it.
yourname wrote:

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Nothing wrong with using customers for R & D, at least according to microsoft. jk
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Is it research if they aren't interested in the results?
Regards,
Robin
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Which demonstrates a critical differnence between the machine tool and software industries.
--RC "Sometimes history doesn't repeat itself. It just yells 'can't you remember anything I've told you?' and lets fly with a club. -- John W. Cambell Jr.
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Dreaming. A new VMC with those specs will cost $30K-$40K. You might find something used for 2/3 that price. Don't bother with benchtop stuff unless you're certain you'll never be running larger parts. Consider adding an automatic tool changer to your features list.
Profiling requires servos and a decent (i.e. modern vintage) controller that can run all 3 axes simultaneously with look-ahead. Beware of low-cost older machines with decent iron but have stepper drives or a controller box Marconi would recognize.
We bought a couple of these VMCs last year, and they've worked out well in terms of reliability and throughput:
http://www.atrump.com/toolroom/Maximill/MAXIP1.htm
joe_d snipped-for-privacy@yahoo.com wrote:

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Look at: http://www.mckeanmachinery.com/inventory/detail.php3?TheKey=MT7562 as an example of used machines. Keep looking, they are everywhere!

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Good info, thanks all.
Yaa, I meant *twice* the machining time of the 50k machines :)
I would be fine with a used machine but don't want something that will require a lot of maintenance costs of course.
Does the ALLIANT CNC VERTICAL MILL W/ANILAM CRUSADER M EQUIPPED WITH: 9" X 42" fit the bill as far as ability to hold this tolerance and also the run time?
I might be pursuaded to go with an enclosed machining center for a little more money since it may work better down the road. What are my price options for the smaller units and also for the less expensive (I'm assuming import) units? Used prices but not for worn out stuff. What are the top places to watch for these as they become available?
Thanks again guys.
Joe
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On 3 Feb 2005 09:42:59 -0800, joe_d snipped-for-privacy@yahoo.com wrote:

I've programmed and run several Alliant w/ Anilam Crusader (circa 1985-90) as well as well as later Fadals (1993+) and Bridgeport EZ Track (1998). Did R&D, as well a 3 axis Aluminum molds. Neither of the knee mills could hold +/-.001 without a lot of work and very careful setups. You needed to consider ALL aspects of the problem if you really wanted to hold your required tolerances. The Fadal could hold .001" on 3 axis w/o *too* much trouble.
I'm sure you could find a used 3 axis knee mill in the $7k range, but that machine would probably have been "ridden hard and put away wet." It won't hold the tolerance you request (without a lot of extra work, and then only just maybe).
Spend more money and you'll be happier in the long run. JMHO. Also, please consider if you *really* need +/-.001" Are you making matched dies? ...duh, I guess not if they're aluminum. But my point is that .001" is pretty tight to hold day in, day out with any kind of efficient speed.
--
Skuke
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wrote:

That was what I was wondering. I would recommend to the OP to find out how the 3d contour will be measured, and go from there...
Regards,
Robin
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I have a Wells Index CNC knee mill. The mill itself weighs 6000 lbs. So it's bigger than your typical bridgeport type knee mill which weigh about a ton. The control on the mill failed a few years ago and I bought a new control from AJAX. Even though about 20 years old and plenty used the machine is quite accurate. So holding .0005" location when boring holes is a breeze. I can get closer by changing the program to compensate for position error because the machine repeats to .0002". So an older machine can be checked for error in both positioning, flatness, and squareness and if good enough then it might fill the bill. I bought my Index mill mainly for complex shapes, not for production. My next mill will be enclosed, the Index is not. Being enclosed will keep the chips and coolant in the machine and allow higher speeds and feeds without throwing chips and coolant all over the place. ERS
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On Thu, 03 Feb 2005 16:19:33 -0800, Eric R Snow wrote:

I agree with you that one can program out (minimize) positional errors by approaching from the same direction to eliminate back lash issues, center drill, drill... With all due respect, true hole position is much easier to hold and measure than the 3 axis contouring the original poster wanted.
My experience with the knee mills (and even the Fadal to a much lesser extent) is that to interpolate a round circle is pretty gosh darn difficult. You wind up with some "egg" shaped hole with dwell marks at the axis' when the ball screw must actually come to a complete stop for a moment to turn the other direction.
Please try it: Interpolate a ~3-4" circle in a rigid piece of aluminum with a good rigid endmill of your choice. Take a few finish passes. Then, without removing the part from the vise (to eliminate other problems like stress/tension relief), measure TIR with a test indicator. I'm pretty sure you'll have at least .001" TIR.
So I think trying to hold 3 axis timing on a cheaper, less rigid machine will be all but impossible.
...just based on my experiences. ...your results may differ.
--
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My point was that lead screw error can be programmed out. The backlash, once measured, is entered as a parameter in the control. One of the first things I did after installing the new control was measure backlash and enter it in. Unfortunately, there is some variance in backlash over the length of the travel. But, the machine will interpolate a hole that's .0006 out of round in the approximate center of travel. Of course, you are right about a smaller machine maybe not being able to hold tight tolerances. My knee mill is 3 times heavier and aboutt 1.5 times as large as a bridgeport mill. So it is massive enough to get good accuracy on heavier parts. ERS
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Which package did you go with? What size servos did you use i.e. inch-pound torque? What did you end up spending on the retrofit?
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On Fri, 04 Feb 2005 08:08:13 -0500, snipped-for-privacy@email.com wrote:

I used the servos already on the machine. If you want, e-mail me and I'll send you my phone number and I'll tell you all about it. Eric
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Try holding +/- 0.001 mm (1 micron) all day, day in, day out. 0.001" is like having a ballfield to play in by comparison.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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Ok, let's put it another way.... what small enclosed VMCs are available and what do they usually run used (for one that hasn't been beat to death)? I figure if there is a machining center with a toolchanger and everything it will probably do what I'm after. I don't need to hold .001" on the whole part but definitely need to for certain areas of it.
JOe
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You need to identity what you need at this point. After reading this group for several years, and selling tools for several years, knowing what you *need* is paramount.
If you spend $7K on a machine that cannot do what you want it to, you have wasted that money, and the time required to buy (and perhaps sell) that machine.
So... Be specific...
Regards,
Robin
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