# Sharing a VFD and DRO Read out between Mill and Lathe



## DickDastardly40 (Jun 8, 2011)

Hi Guys, long time no see!

I am considering changing my Mill and Lathe motors to 3 phase to utilise a Vector Frequency Drive and wonder about the wisdom of buying 2 motors wired to 3 phase plugs with a single VFD with a socket output so I can plug in which ever machine I happen to be using. Obviously the VFD will have to be man enough to drive the larger motor on the mill. Both machines are adjacent so I don't see any wiring issues and a remote speed control would work nicely I think.

On the same frugal lines I was wondering about a DRO install where potentially the measuring scales of both machines can be swapped between a single display mounted as best suits the length of the leads.

What do you think or am I looking at a false economy?


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## mzetati (Jun 8, 2011)

The Shumatech DRO-550 has a 5 inputs, maybe more can be added.
Dunno about availability of the product (it was sold through a power-buy).

http://www.shumatech.com/web/products/dro-550
http://www.shumatech.com
(Usual disclaimer applies)

I'm happy with the old 350 version, which works with 2x24bit scales (though there are some protocol converters designs available).
Another option could be the DRO-350 completed with the DPU-550 unit.

When wiring the scales on my mill, I sent the X & Y wires to a box fastened below the table, from wich a single cable (thee flat one, a common computer network cable) lead the power and signals to the DRO. That same idea could be applied to Your needs, if You go for the shared DRO solution.







Marcello


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## BillTodd (Jun 8, 2011)

First thing to remember is that VFDs are not three phase generators, they are motor drivers and should only be used to drive the motor. Ideally they should be set up to drive a particular motor. 

Secondly, VFDs do not take kindly to being connected or disconnected while on load.

That said, it is perfectly possible to to switch between two motors, or the two windings of a dual speed motor, without any problems. I have been doing the latter for a few years now on my HLV-H and have a similar set-up on my Haighton mill.


If you choose to use a plug and socket arrangement for switching motors, then you really ought to consider mounting a micro switch operating on the socket locking cover so that when the cover is moved (as it must be before removing or inserting the plug) it stops the VFD instantly. 

Most VFDs have multiple stop modes; they usually ramp the speed down and/or apply DC braking to the motor, but the mode you need for this application kills the power and allows the motor to run to a stop.

Some VFDs have the option of using two sets of motor settings , some only have the option to use a second set of start and stop ramps , having either would be very useful if you are going to try running two machines.

Bill


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## mzetati (Jun 8, 2011)

my ideas about VFDs are so vague I would not risk suggestions about wiring them, 
my post was entirely on the DRO part of Your question.
Sorry, for not being clear.

Marcello


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## kvom (Jun 8, 2011)

Given that a lathe and mill may need different parameter sets, and that VFDs ar not particularly expensive, I'd go with separate ones. If you want to use the VFD(s) for speed control, then you probably want the units mounted differntly as well.


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## TroyO (Jun 8, 2011)

The DRO 550 is back in stock and shipping now. I just got one and finished getting it installed last week, as a matter of fact.

The DRO 550 has two machine modes... mill and lathe and you can switch between them. You can set up the Mill Mode to read scales 1,2 and 3 and the Lathe Mode to read 4 and 5 (Or any combination thereof...) so it should work well on multiple machines. I considered setting mine up that way, but as yet I haven't installed scales on the lathe.

I also have an older DRO 350 so I probably won't bother... I'd have to move the machines to do it so it's easier for me to use 2 displays.

Anyway, before I wander to far afield of the original question, LOL... yes, the DRO-550 can handle 5 scale inputs, and you could potentially add a physical switch if you needed more than 5 in total (But no more than 5 at time) so you could have 2 machines fully configured and switch easily between them on a single DRO.

VFD I have no info about.


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## MachineTom (Jun 8, 2011)

I've done a number of VFD installs. Issues to look at, the vfd is motor specific, #of poles 2,4,6, KW rating, Full Load Amps. You would quickly run into problems if one motor is 2 poles (3600 rpm) and the other 4 (1800) reprograming the VFD each time you switch machine, it would quickly become a problem if you set the parameter to 4 pole and used it on a 2 pole motor, not a great idea.

Small HP vfd's are cheap enough that you shoul just buy one for each machine. A lathe will benefit more from a VFD than the mill in my experience. I do have one on each, but the lathes were done long before the mill.

When setting up the VFD, use remote logic control for each function. The VFD should be away from Chips in a vented enclosure.


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