Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: mikemill on January 04, 2008, 12:20:30 PM

Title: Spindle Control
Post by: mikemill on January 04, 2008, 12:20:30 PM
I have retrofitted an old Orac lathe, all is working but the spindle direction is erratic. The motor is controlled via a VFD and is set in correct direction, the VFD  in turn is controlled via a relay on breakout board. When I push spindle button on Mach Turn manual screen the spindle sometimes rotates in opposite direction, If I then turn machine off ( control electronics included) and then on again spindle rotates in right direction.

Anyone got an idea whats causing problem?


Title: Re: Spindle Control
Post by: jimpinder on January 05, 2008, 05:04:51 AM
I am a little puzzled. From what you are saying, your spindle motor on your lathe is controlled by a variable frequency drive. Is the direction hard wired on the drive or a switch or push button ?? A single relay on your breakout board controls the motor on/off.

If the above is correct then the fault cannot lie with Mach 3 becasue it does not have control over direction. The fault must lie with your VFD.

I am puzzled by the VFD - mine has two inputs, one for M3 (forward) and another for M4 (reverse). Either one can be switched at any time, BUT NOT BOTH together. there is no forward/reverse switch as such. How does your VFD switch to reverse.

What I would try is rewire the leads between the VFD and motor so you are effectively driving it in reverse, and then reverse the VFD and see if the fault repeats itself in the reverse direction. It could be that the electronics/ relay/ or whatever that controls the forward reverse is a little sluggish.
Title: Re: Spindle Control
Post by: mikemill on January 05, 2008, 06:59:29 AM
The VFD is set to external contol, the output from relay on breakout board goes to forward and reverse on VDF. thus code M03 / M04 should control spindle CW / CCW
If I contol spindle manualy the direction is erratic. could it be the relay bounces when I turn on machine?

Thanks   Mike
Title: Re: Spindle Control
Post by: jimpinder on January 06, 2008, 03:15:58 PM
We will have to get this bit out of the way, before we go forward -

Your VFD has two connections - Yes !
Is one connection for M3 and the other for M4 - OR - is one connection for Go/Stop and the other for forward/reverse. It does not matter which it is, but it is essential we find out which one it is.

Mach 3 simply puts out a signal on one pin for M3 (forward) and another signal on another pin for M4 (reverse). The pins are not on simultaneously (and should not be). My VFD shows a fault if both pins are on simultaneously. This is relatively easy to connect - and it sounds like you are along that road already.

If your VFD requires one signal to tell it to turn on/off and a second signal to tell it to go in forward/reverse direction, this can be simply achieved with a couple of diodes.

If you say you have retrofitted this lathe - is there a book or data for the VFD ???
Title: Re: Spindle Control
Post by: jimpinder on January 06, 2008, 03:44:48 PM
I have just googled this VFD and come up with this link to a forum. There is a chap on there who seems to know quite a lot about it.The link is at

The connections to your VFD bear no comparrison to those on a modern VFD

We now appear to have, as standard 6 pins.
1. M3 connection 2. M4 connection 3. 0v M3/M4   4.V+ connection 5. Speed voltage reference 6. 0v speed regulator
Pins 1 and 2 connected to ground (via a relay) give forward or reverse drive - both cannot be "on" together
Pins 4.5 and 6. which are electrically seperate from 1,2 and 3 give a +v and 0v reference to attach to a potentiometer and pin 5 is the return from the pot wiper, which sets the speed.

The connections shown for the Oracle VFD are nothing like that. You require momentary contacts on the forward or reverse pins (not on/off switches) and the speed sensing seems to be somehow all intertwined with it .

Unless you are a competant electrical guy, I would suggest, in all honesty,that you get yourself a more modern VFD that has standard connections. On the standard set up, Mach 3 has the relevant outputs - M3, M4 and PWM (to run a digispeed controller to control your VFD) - and THEY WORK.

I have had M3 and M4 going for some time, but I also fitted a Digispeed two weeks ago, and now I can control the spindle speed to 1 r.p.m from the computer. It is marvellous.

Without being a pessimist, I think you will spend a lot of time with your old Orac, and all you will manage is  to get forward and reverse going satisfactorily - and that will still leave the speed control up in the air.

Anyway - have a look at the link and see what you think ???