Hello everybody,

At work we're running after a decent contract for aluminum molds. At this moment we don't have a machine to deliver goods, so we are on a thin string of buying one or building one.
There are few decent products out there, but the price to pay for them is pretty hard to come by. Some of them go over 3 times or more the budget of a build. For just a little over the build, commercially, sizing is limited.
We'd require something that can work in the area of 2500 by 3500 by 350 mm.

If, there will be something out of it, here it goes, attached a basic idea.
This will be my eighth CNC so far, and I would mention, that all the others are junk. Good for hobby, but not professional.

So, here we go:
1. Aluminum: - I am interested in high speed machining with light cuts. If I'll be able to go to 5 mm depth with 4-6 m per minute I'm happy. I'm not into the hard deep milling, because for this kind of job is worthless. Yeah, great for roughing, but when I have 2 sqm of finishing, I don't want to sit 2 months for it to finish. So, light cuts, and high speed. My actual machine, which is like an old tractor, will do 2 - 3 mm depth at 2 m per min. But the tool will wear out in 2hrs due to vibration. 0.5 ~ 1mm is the safe with it.
I usually mill with single flute cutter from Datron 4, 6, 8mm at 24.000 rpm. I am considering to go for 40.000 - 60.000 rpm in this case.
2. Construction: - 2500 x 3500 total dimensions. Frame will most probably be made out of steel. Leveling will be made with epoxy. One bucket, hoses, and pour on both X axis supports. This way I believe, I will get it planar. For the main table, I will fill the base with epoxy granite, inserts, and an extra coat of epoxy which I will mill afterwords. Work holding, most probably a sacrificial ally plate with venturi labyrinth. Gantry, will be 5 or 10mm steel sheet, bent, ribbed inside, and enforced with a 100mm pipe. Not sure yet if I'll fill the gantry with EG or not. On one hand is good for dampening, but it's bad for inertia. Considering that I'll go for the fast and light cuts option, I tend to go for the empty idea.
3. Drives - helical good rack and pinion are hard to come buy, so I am considering a 32 dia ballscrew with 32 mm pitch. Fixed screw and rotating ballnut. 2 per X, one per Y, and one per Z.
4. Motors - I have seen some closed loop drivers for steppers available. If that will be the case I will probably opt for something in the range of 12, 20 or 32 NM steppers. It all depends on weather I'll fill up the gantry with EG, or not.
Ideal encoder placing would've been straight on the ballscrew, but in my case I'll have to settle with on the stepper axle. Servos are the other option, but never worked with them. 400W, 700W doesn't translate much in my head at this moment. Also, I'm clueless about their torque, gearing necesities, rpm and so on.
4. ATC - this would be a nice option to have. Had worked with ATC before, but never tought about implementing one. I'm quite fond of these chinese spindles out there, or I might have been lucky with them. I have seen a version with 24.000 rpm and ATC option for ISO 20. Not sure how does it come by, with locking and releasing. Via air, or via solenoid. Also, haven't seen one for 60.000 rpm with ATC.
5. Mach3 will be the way to go, tough people that I spoke with, machine sellers, constantly tell me it's worthless in the professional environment. Same machine will triple it's speed only because of their dedicated drivers and software. Don't know what to believe, is it hype or plain facts. True, theirs run with 1.5 m / sec!!!

The reason I went for this layout instead of a classical one, is because it looks, at least in theory to be easier to level/square and all. Also, the gantry supports are taken by the table. And table or lower frame, I have to do it either way. So that's another plus. Jobs will probably be fed via the forklift so it will be easier this way. Probably it'll come with back aches when doing a small job, but it's a win/lose situation.

If we'll decide to go with it, instead of buying, I'm hoping at 4 months with it.

I might be very wrong about the logic of it, so if you guys have walked this path before, I'd appreciate your thoughts.

Thanks,
P.