[GalaticDan]

Questions all to cnc bods:

I've got an Allen Bradley F series servo (weight 18Kg) 3 phase 240v AC. I've been working on building my own CNC machine for sometime and have collected parts from THK slides to DC servos and Gecko drives. I would like to think I've a solution for main spindle drive that mounts into a chuck but need some suggestions, I accept I could have completely gone the wrong road on this one.

Materials:
I would like to use this 2.2KW motor as my main spindle drive for machining of aluminium block (50mm thick) and sheet stainless 2-4mm thick 304 grade.

Mounting:
My idea is to mount the motor directly on my Z axis slide and make fit a suitable MT2 attachment for tools and chucks. This does mean my heavy spindle motor will move up and down on the Z axis. I've spoken to a spring maker and he can make me large extension springs to take the load off my Z axis gecko drive controller and motor (same way shopbot do). I am worried about torque directly on the spindle motor when maching my chosen materials. I've got no idea how much torque will be applied to my spindle when machining the above materials but do have figures from the motor's manual:

F-4075 motor radial loading:
500RPM = 41.7Kg, 1000RPM=33.1Kg, 2000RPM=26.3Kg, 3000RPM23.1Kg
44% of above figures for axial loading.

Now I should say that the gantry travel is fairly large 600mm in the Y direction, 1300mm on the X direction and the spindle motor has the potential to move 200mm in the Z (but it's more likely to be 100mm max.).

1). Firstly I guess, does my idea sound ok or not? I've seen this mounting method on wood cnc machines.

2). Is my motor suitable given these figures and the metal I wish to machine for a direct mount of a chuck onto the spindle in some manor?

3). Is this going to overload my DC servo motors and Gecko drives? I.e. the force required to just move the motor over the gantry in all directions and then machine aswell?

Many thanks for your replys

GalaticDan

[Kmed]

The sping idea will work, or there are two other options. Cantalever it, with a pull and weight, to balance the head (with no ball screw / exact weight or really close, or you can use a pnematic cylinder with a pressure valve with the length you need and balance it that way. I like the air cylinder as it adds minimal weight (vs cantaliever), and is linear vs the sping. All you need is a little portable air tank, and a small compressor, or just your average compressor (10 gal or so). I dont know about your servo motors, but as long as they can resist pull down if you are taking a heavy cut, with an up spiral, then you will be fine with any of the above options. (BTW the air cylinders, were used to balance our big 5 zxis routers at my old shop, and worked well, and the heads weighed upwards of 600lbs.).... I have some pictures I could upload (not great) if you would like.

Good luck.

[Al_The_Man]

I would guess that your biggest problems machining those materials is going to be rigidity. Many have found this out the hard way when converting drill presses for milling etc, even these do not do the job for the above reason.
Al