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Need some guidance on vfd control for mill while also using existing control. Potentiometer?

Sincerd

Aluminum
Joined
Jul 22, 2023
My mill has 4 motors between the power feed and the horizontal attachment. I really only want the main spindle on a vfd and I want to be able to control the speed with the vfd wired to a switch, or something that looks like a potentiometer, that I will run to the existing control box. I would still like the power feeds to be controlled by the control box as well as start and stop from the motor.

Is all this even possible? Because I'm guessing that power needs to be ran to both the vfd/motor and existing control board. Is there anyone that can point me in the right direction? I don't even know where to start. Not finding a lot of similar situations.

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It SOUNDS like you want to isolate the spindle drive, and run it with the VFD, using the normal spindle controls, while leaving the rest of the motors powered with incoming 3 phase, using their normal controls.

No reason you cannot do that. I would rewire the spindle "on" switch to go to the VFD control, and ditto with direction. The spindle power would bypass the spindle "on" switch and go direct to the VFD input, so you are not always turning power to the VFD on and off, you are just telling it to drive the motor, or stop.

Aside from using the correctly insulated wire for the control signals (they may be in a box with higher voltages), it sounds very do-able to me.

Does that cover it, or have I missed something?
 
To add to the above, you would essentially be replacing the spindle motor contactor(s) with the VFD. You'll probably still need some interposing relays or to do some rewiring because the VFD will expect 24VDC controls and the existing controls are probably 110Vish.
 
You also have a 2 speed motor, looks like a 4P/8P, so would be helpful to see the motor tag to determine how it should be run. Most likely 4P, but by adjusting the motor speed with the VFD, you loose the mechanical advantage of the belt ratios. The motor would be directly connected to the VFD, you could replace the three lower right buttons with a stop (unguarded), run (guarded) and a 2 way sustained forward/reverse switch, run the VFD in 3 wire control wired directly to the VFD low voltage inputs. You would need a separate enclosure for a speed pot. You would not use the motor contactors, would look at the wiring schematic to see if they can be removed.
 
No reason to remove anything, it just makes it harder to return to previous condition.

For just one control and a switch or so, the VFD probably has both a dedicated voltage for the speed control, and a general control voltage.

You would disconnect the spindle drive switch from it's existing wiring, and connect the control voltage output and the correct input on the VFD to the switch. Shielded wire would be advised, rated for the voltages o any other devices in the same control enclosure.
 
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Finally getting around to start doing this. I found these in a post with the exact same Mill. Not finding a whole lot of info about this Mill other than that. You guys have any suggestions on specific vfds or switches?
 
Assuming that the two drawings describe everything.

1. Disconnect the three wires from the right side of MS4 to the right side of MS3. Insert your VFD between MS3 and M2.
In first drawing second line, remove connection to MS4 and connect to M3. You have emergency off by your red button.

2. Or disconnect the three wires from M2. Connect R, S, T to the input of VFD and the output to M2.

What does M2 nameplate say?

MS5 looks like a self-destruct connection.
 
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Assuming that the two drawings describe everything.

1. Disconnect the three wires from the right side of MS4 to the right side of MS3. Insert your VFD between MS3 and M2.
In first drawing second line, remove connection to MS4 and connect to M3. You have emergency off by your red button.

2. Or disconnect the three wires from M2. Connect R, S, T to the input of VFD and the output to M2.

What does M2 nameplate say?

MS5 looks like a self-destruct connection.

That's what the guy in this thread said to
 

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You can get busy with a ohm meter and see what the story is.
A convenient connection for a star winding connected coffee warming plate. :drink:
 
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Somebody will know eventually.

I would not put any speed potentiometer in the box shown. That thing is crammed already.
Use a double sided thread bolt with a hex flat in the middle. Use that in place of one of the three flat head counter sunk screws which hold the green box.
On the screw sticking up mount your new speed control box.
 
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