Emco F3 conversion - electronics and controller

[fastbike]

This is a supplementary thread to the others detailing the conversion of my Emco F3 mill, in which I will detail the changes to the electronics and some considerations for selecting a controller.
The original electronics are switch gear that are typical of the period: good quality equipment but very 1980's in execution. The power supply is 3 phase 400V AC, and interesting has no neutral wire, read on. Power to the main motor is controlled via a two speed dahlander switch which allows the motor windings to be connected as delta or star to vary the speed.
Supply to the existing X Axis power feed (the only one originally fitted) is via a transformer and the variable speed is handled by some crusty looking electronics on a board in the control box.
The coolant pump is a 3 phase motor and has a simple 3 pole switch.
The DRO is an obscure brand (Aurki) and requires 230VAC. This is supplied by one phase and connecting the DRO's neutral wire to the mill's protective earth - thus relying on the tie between the neutral and earth at the building's electrical installation to carry the return current. IMO, this is not a particularly safe way of doing it but I'll be ditching the DRO once I have the CNC conversion completed so it stays at this point in time.

The manual controls are placed on a sloped panel facing the operator - this panel sits atop the control box which is a fabricated steel cabinet bolted to the rear of the machine column. Dimensions are roughly 500H x 250W x 190 D, with the control panel protruding another 195mm.


The slightly later F3B model changed the shape of the control box - it does not slope back under the operator panel - and I think a design similar to this could provide additional internal capacity for the gear that needs to be installed.

There is sufficient room to make the box 50mm wider (although I'd like to reuse the door), or make it deeper.

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[fastbike]

I'm also keen to retain some elements of a manual mill, i.e. be able to switch the spindle on at slow or high speed, and move the X/Y/Z axis manually in a variable spped jog mode (including rapid).
I've mocked up a layout of a replacement front panel in CAD, here's the first iteration. I've made this so it is the same dimensions as the existing operator panel.

The Ready and Fault are indicators only (not switches)

[fastbike]

I'm leaning towards a Eding CNC 720 board. The vendor has been responsive to my questions and it comes complete with decent software, connects via Ethernet, mounts onto a DIN rail, is 24V compatible, supports E Stop inputs, 2 coolant outputs etc etc.
I already have CL86T closed loop drivers from OMC Steppers online. These will be mounted to a hinged backplane.
The other items are the power supply for the motors (3 phase 400VAC to 48VDC, 960W), power supply for the controls, spindle motor switching contactors and protection, a disconnect relay for the E Stop button, relays for the flood/mist/light main supply breaker etc.
All in all quite a bit to fit into the box. I'll need to do some layouts to check it fits within the existing enclosure, or I can get a sheet metal fabricator to fold up the parts for a larger unit that will fit in a similar place to the original Emco item.

[fastbike]

OK, have done a little planning for the equipment that needs to be accommodated in the control box:
1 x 3 phase MCB
1 x 3 phase 400VAC coil (main contactor)
48V 960W 3 phase PSU (for stepper motors)
24V 240W 3 phase PSU (for general controls)
1x contactor for stepper motor PSU and spindle (E stop)
3 x contactors for spindle (dahlander control)
1x contactor for pump
1x contactor for mist
4x stepper drivers
1 x DIN rail mount EdingCNC 720 controller board with BoB
1 x DIN rail mount Eding UIO-10 auxillary board
various switchgear for manual/CNC controls
2x fans for coolimg

I've done a rough layout and will design a control box 100mm deeper than the existing.

[fastbike]

I've drawn up a prelim design for the control box. This follows the shape and form of the existing one, however it is 50mm wider, 100 deeper and 30m shorter.

The additional depth was required to fit the components and allow some room for a future fourth axis. I made it 30mm less tall so I can use the two M8 threaded holes in the back of the column to attach the reconfigured Y axis motor mounting plate. As this meant the existing door could not be used I made the enclosure 50mm wider to provided better airflow for cooling.

I have sent the drawings out for a quote from a local sheet metal fab shop. The box will be TIG tacked on the joints and then silver soldered along the seams.

[fastbike]

I've had one reply back for punching and folding the sheet metal, waiting for the other one. In the interim I've started drawing the circuit schematics using DIPTrace which is a useful way of documenting the parts I need and exporting the BOM.

[fastbike]

Ok, so another back. Double the price and a 5 week lead time. I think that helps me to decide

[fastbike]

While I'm waiting for the controller box to be cut and folded, I've gone back to doing the schematics for the controller.

Here's a post I've done elsewhere to figure out how to connect the driver alarm outputs to the controller.
https://www.cnczone.com/forums/stepp...-software.html

[fastbike]

I'm giving the front control panel some initial thought. The existing one is 2mm thick aluminium, painted black with screen printed graphics.

The replacement needs to be durable and affordable. A self adhesive vinyl over a blank alloy sheet would be affordable, but may not be that durable. A screen printed overlay onto a alloy panel will be durable but not that affordable. Another option would be some type of transfer on the underside of a transparent panel, polycarbonate is durable.

Time to talk to the experts. Somebody like this

[fastbike]

So the controller arrived today. Yay. Just waiting for the tinware to be processed so I can start the controller box build.

[fastbike]

I've largely completed the schematics for the electronics. I'll put up a few posts over the following days to document the design.

First off is the main power circuitry of the machine. The mains supply is 3 phase 400VAC, which is controlled via a contactor and two momentary switches on the main control panel: the first energises the coil of the main contactor and the second de-energies the coil to give a zero volt release mechanism. A NC switch is included so opening the door of the control box will cut power.

Power for control circuitry is provided by 24VDC SMPS. This is always available if the machine is powered up. A DC DC converter supplies 5VDC.

Power for the spindle and steppers is supplied via a secondary contactor, where the supply to the coil is broken by the EStop button being activated or the limit switches being triggered. This ensures in the case of a fault (or the EStop button being activated) the spindle and steppers will stop (the controls will still be active). A fault feedback LED on the operator panel will light if the contactor resets.

Power for the steppers is supplied by a 3 phase SMPS which delivers 960W at 48VDC.

[dazp1976]

When/if I ever get around to sorting out my limit switches I was debating whether to link to the e-stop.
Now I'm thinking not, because my home position will be a back-off setting from a limit switch.
Could potentially cause me a headache.

[fastbike]

When/if I ever get around to sorting out my limit switches I was debating whether to link to the e-stop.
Now I'm thinking not, because my home position will be a back-off setting from a limit switch.
Could potentially cause me a headache.

Surely the home switch should be physically between the limit switches. see this post.
https://support.edingcnc.com/support...d-home-switch-



If the limit switch is tripped, we want the steppers and spindle to be cut off to prevent damage. Although maybe a momentary manual override to allow jogging to back within the work envelope ?

[fastbike]

So the revised diagram with the Limits override switch to allow manual jogging to get the tool back within the work envelope. Hat tip to dazp1976 for getting me to think the idea through

[fastbike]

One other question I have is the indicator LED module, shown as LED1 on the circuit. Ideally I'd rather this was not being fed from the 400VAC, as it is a 230VAC part so requires extra voltage dropping which introduces thermal issues. The alternative is to use a 24VDC LED module connected to the output of the SMPS: this simplifies the circuit driving the indicator but places the 400VAC switch and 24VDC indicator next to each other on the back of the illuminated power switch (Eaton M22-DL-G). Although the parts are rated at 500V, this would require some physical separation to safeguard against the 24V coming into contact with the high voltage.

[mactec54]

Surely the home switch should be physically between the limit switches. see this post.
https://support.edingcnc.com/support...d-home-switch-



If the limit switch is tripped, we want the steppers and spindle to be cut off to prevent damage. Although maybe a momentary manual override to allow jogging to back within the work envelope ?

It is quite common to use the Limit Switch as a Home switch, so saves a switch and wiring, what an axis normally does when Homing is hits the switch and then backs off the switch by a number you choose to set in the Homing Parameters, Once Home is set, soft limits then protect your machine, and should never be able to ever hit a Limit Switch, if everything it setup correctly.

[fastbike]

It is quite common to use the Limit Switch as a Home switch, so saves a switch and wiring, what an axis normally does when Homing is hits the switch and then backs off the switch by a number you choose to set in the Homing Parameters, Once Home is set, soft limits then protect your machine, and should never be able to ever hit a Limit Switch, if everything it setup correctly.

I can see how that would work, and the EdingCNC manual mentions a similar homing sequence: traversing until the Home switch is triggered, and then reversing until it resets.
I like your expression " if everything is setup correctly". I have too much real life experience to rely on that so for the cost of 3 extra switches (I already have the required wires) I'm going for the "belt and braces" approach

[fastbike]

Which segues nicely into the Limits circuit.

This comprises 3 sets of two NC switches feeding into a quad opto isolator, and the Darlington outputs from those connected in series to control a low power relay. The relay is a SPNO configuration. The operating state is that normally all limit switches are closed so each of the opt isolator inputs are conducting, so the relay is active and is closed.

If any limit switch activates (goes open) then the associated opto will stop conducting and the relay will deactivate and and remove power from the motor contactor. An (active low) signal is also sent to the controller's external error input which will shut down some of the outputs (steppers, spindle, coolant etc)

Recovery from the fault condition is via the override switch (shown above in the power circuit diagram) and jogging the appropriate axis back into the work envelope. I thought about restricting the jogging speed if a limit error has occurred but ruled it out on the basis that this is an exceptional situation and is covered by a printed recovery sheet.

[mactec54]

I can see how that would work, and the EdingCNC manual mentions a similar homing sequence: traversing until the Home switch is triggered, and then reversing until it resets.
I like your expression " if everything is setup correctly". I have too much real life experience to rely on that so for the cost of 3 extra switches (I already have the required wires) I'm going for the "belt and braces" approach

Most CNC Manufacturers today only use (1) Proximity switch per Axis works very well, saves wiring and easier to trouble shoot when there is a problem, I'm the same as you, but with a quality control like the Eding less can be better. On a machine like you are doing it won't matter how many switches you use, just remember wherever your Home switch is this will be your work envelope unless you set up the soft limits outside of the Home switch position your max travel will be restricted by where you put the Home switch, which becomes a problem when you want that extra 5mm of travel

[fastbike]

... the Home switch, which becomes a problem when you want that extra 5mm of travel

I'll bear that in mind when I finalise the position of the home switches. I have slightly increased the X and Y travel by changing the mounting of the ballscrews cf the original acme screws so happy to give up a few mm.