Re: [CAD_CAM_EDM_DRO] Re: Monarch conversion to VFD

Marcus & Eva wrote:

> Hi all:
> I need some help with a decision.
> I negotiated to buy a Monarch 10EE lathe about 4 months ago.
> The machinery dealer was (and is) having problems getting the old DC drive
> to run up to speed.
> The last 4 months have been spent making foolish promises that they are
> unable to deliver on.
> I have heard that several people have made a conversion to AC with a VFD and
> that they are happy with the result.
> Is this a big job?? (I mean electronically...the mechanical bits I can
> handle.)
> What could such a conversion cost??
> Should I consider this whole fiasco a dealbreaker? They want $10,000 CDN
> for the machine which they say is otherwise totally rebuilt. (I've never
> seen the machine, so at this point I'm taking their word for it)

The tricky part is getting an AC motor that is in the same frame, or at least
something that you can adapt to fit. Apparently, in the 10EE, that is not too
hard, as I believe it is direct belt drive. So, you mostly need an AC motor
about the same diameter, with about the same shaft dimensions.

Modern VFDs are really quite nice, I've got on on my mill, and will have one on

my new lathe when it is ready. If you just want to use the lathe (at $10K CDN,

it sounds like you will be!) then see if they will do the conversion.
Electrically,
it is real simple. You could rig up a 3-position switch, for
forward/off/reverse,
and a speed pot. Or, you could rig up a couple of relays and have forward,
reverse and stop buttons. Electronically, all you need are a speed pot and
the switch arrangement you prefer, wired to the terminal panel in the VFD.
If you have 3-phase power, that's even better, otherwise just get a larger
VFD than the motor nameplate rating, by 50% or so. (Ie. for a 5 Hp motor
and single phase power, use a 7.5 HP VFD.) Make sure to get the heavy
duty braking resistor, as the VFD will need to slow the lathe down and dump
energy into a braking resistor. If you don't have this, the VFD may fault,
or just take forever to stop the lathe.

Jon