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HP Limitations

Henry L.

Plastic
Joined
Feb 22, 2009
Location
Denver, CO.
I'm looking for a CNC machining center to run in my home garage.
I only have single phase and will be using a phase converter.
I'll be building a converter from a 20hp motor I have laying around.
How big of a cnc mill (HP) can I get away with before running into problems?
Thanks.
 
I'm looking for a CNC machining center to run in my home garage.
I only have single phase and will be using a phase converter.
I'll be building a converter from a 20hp motor I have laying around.
How big of a cnc mill (HP) can I get away with before running into problems?
Thanks.

Depends on a few things but 10hp would be a safe estimate.
 
I just bought a cnc lathe for residential service. The spindle is 10hp, but the two axes are 3hp each, then the hydraulic pump is another 4hp... See where I'm going with this?

The machine is rated at 63A 3ph 230v and designed to be used with a 25kva transformer if needed (440 service).

My solution was to buy a grossly over sized vfd because once you start looking at 40hp idlers you might as well go vfd, as you can't buy the supporting hardware (caps, starters, etc) for what you could buy the whole vfd for (used). I'll still need a disconnect switch, but that's it (the machine has fuses, the vfd has over current protection that I can set appropriately, and the circuit will only feed that vfd so line protection from the main panel will suffice).

The only real question left is how well will the drive handle the dynamic loading due to the DC motor drives and their potential instant on switching (especially with relation to rapid traverse). The spindle drive itself is not regenerative for braking (it uses a disk brake like a car), so that limits the amount of current fed back into the line (could be an issue with over current faults otherwise).

Worst case scenario is I will need another "buffer" motor in addition to the hydraulic pump (that will always be on) to help dampen the demand spikes. We'll see how it works on thursday when the drive shows up.


Something else I discovered in my quest for a power input solution, was that my lathe uses the phase rotation (the angle and timing between each of the 3 legs) to clock the servo drives (clocking is keeping them sync'd together) rather than it's own integrated crystal or whatever. So if you were to use RPC generated electricity, you'd need a vfd to feed that clocking circuit or else you could have accuracy and repeatability issues to no end. After all, without accurate timing between the axes, you cannot follow a designated path. If the control didn't fault out on you (the cnc control that is), you'd at best relegate the machine to a "point to point" machine and that's pretty much worthless for anything but straight lines and poking holes.
 








 
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