Opinions For Spindle HP

[DamonJones]

So I have an old Lagun mill that I've converted to CNC. It works great but I am considering using an AC servo for the spindle. The current setup uses a 5hp 3phase motor at 1750 rpm. It has a variable belt clutch setup that is easy for speed changes but still a manual process. Plus I'd like to get rid of the 3 Phase if possible. So here's the question. What would you consider as a minimum HP or KW rating for the new motor? My thought would be if I pickup max RPM to say 4000 I could lose some HP and keep the cost down. I'd eliminate the adjustable clutch and drive the 2 speed gear box directly.  That way I still could have good slow speed torque if needed.

This is a home system so production is not an issue. I don't mind cutting slower but I don't want to cripple the machine either.

[Hood]

On my Beaver Mill I put an Allen Bradley MPL-B580J motor which is 8KW 34Nm cont 87Nm Peak. It is well over powered and I dont have any need for the low range in the gearbox, I can put an 8 inch collet spanner on the collet holder and start the spindle at 1RPM and only just manage to stall it, any faster and no chance.

On the Bridgeport, which I am re-doing at the moment, I have put a F4050 Allen Bradley motor which is 6.7Nm cont torque and about 2.8Kw and although I have not really done much with it yet it seems plenty.
Hood

[DamonJones]

What size driver does the F4050 require?

[Hood]

DSD-030 although you could probably get away with a DSD-020 if you also had an active shunt.


Hood

[DamonJones]

Could you explain the active shunt to me? Save me a bunch of research time. Thanks

[Hood]

The Allen Bradley micro drives do not have internal shunt circuitry so if you try and accelerate too fast or slow down too fast with biggish motors they will trip on Bus overvoltage. The active shunt is a unit that contains the circuitry and also a shunt resistor. I use them with 020 drives on the X and Z of the Beaver mill.

The full size drives have internal circuitry and shunt resistors so an active shunt is not needed and if  more shunt resistance is required you can attach to the external terminals.
Hood

[Hood]

Here is an active shunt, just so you know what to look for.
http://www.ebay.co.uk/itm/ALLEN-BRADLEY-2090-UCSR-A300-ACTIVE-SHUNT-REGULATOR-/230584345515?pt=LH_DefaultDomain_0&hash=item35afe5e3ab
Hood

[DamonJones]

Is there a particular unit you recommend? Or a rating that is required?

[Hood]

Not sure what you are meaning, if its the active shunt you are talking about there is only 1 size as far as I am aware.
Hood

[DamonJones]

Yes the shunt, I'll see what I can find. Sorry AC servos are new to me.

On another note I noticed in one of your other posts talking about line drivers for the DSD drives. What levels are they looking for on STEP and DIR? Do you have a sample schematic of your solution?