Conect 121 CNC Lathe Project

[mtrehy]

Hi All,

I picked up one of these today and plan to get it running for hobby stuff.

I will post some pics during the week but it looks pretty much unused and came with 2 original manuals, bbc computer, control box, monitor, 5 1/4 floppies etc. I don't need to do anything particularly exciting with it and it will probably live at the school I teach at as a training / demo machine only. I do want to be able to cut threads.

Last year I built a cnc plasma using axbbe board and uccnc control software so I have some knowledge although it's fair to say I am good at following instructions rather than fully understanding the electronic principles behind it all.

I want to get this running off of modern software though and ideally (similar to how I run our cnc mill and my plasma) produce code in Fusion 360.

Ideally I also want to be able to use this machine semi-manually, i;e control spindle speed and axis movements from switches.

The spindle motor is a 0.37kw GEC 180v dc motor (I assume original).

My initial thoughts are to use a chinese 400w panel mounted motor controller for speed, and a couple of Nema 23 closed loop steppers for the axes. One thing I am not clear on is whether the spindle needs to be controlled? I appreciate it needs to provide accurate speed via the optical encoder for screwcutting but is that information used to position the axis or also to tweak spindle speed?
I like the axbbe motion controller that I used on the plasma but it is quite expensive - I wanted an ethernet controller on the plasma because of the interference issues from the plasma with usb. I assume this isn't such a problem with a cnc lathe? Can I get away with a cheap chinese usb controller?

Very interested in peoples thoughts on this project. I see a few people on here have got these little machines going so any advice greatly appreciated!

Cheers

[m_c]

If the original spindle drive still works, then I'd use that.
Failing that, I'd either buy a KBIC board, or a Sprint drive, as they'll give more stable speed control than a cheap chinese controller.
One thing to be aware off, is these types of SCR drives often have non-isolated inputs which sit around half of their supply voltage, so need isolated speed control.


Spindle encoder wise, the original setup on these has a single slotted disc, and a multi slotted disc.
In terms of what you'd need, will depend on what motion controlled you use.

You need to be aware that not all motion controllers support turn/lathes and threading.
I'm not sure what UCNC's current status is regarding lathe functionality, or what they'd require in terms of spindle feedback.

The ballscrew setup on these is very basic, and ultimately rely on the stepper motors for endfloat control.
I personally wouldn't bother with a closed loop setup on one of these, as they won't improve accuracy.
Most accuracy problems I had with mine was due to the noodly Myford ML10 base machine flexing.

[JohnHaine]

The venerable old Mach3 system works well on a lathe, I use it on my converted Super 7. It works for threading using a single slotted index on the spindle. Mach3 just uses this to tell it when to start each threading pass, it doesn't control spindle speed , just assumes there's enough power not to slow down. That works for me, I don't cut very deep threads. You have a 1/2 hp motor, could be fine, just try it and see. I believe Mach4 can use encoder pulses from the spindle for finer control, not sure about that. To reiterate his point about the controller, if you want to control spindle speed from the PC you need to make sure it's isolated. If you're happy with manual control there's not a problem. I have a Denford Novamill of the same vintage, it originally used a Sprint drive but I use a KBIC drive with manual speed control.

As m_c says, there's no point in using closed loop steppers, you might as well stick with the original motors, at least to start with. Upgrade if needed. They will probably work much better with modern microstep drivers.

Regarding the PC interface, I use the CNCDrive UC100 on both my lathe and mill, USB interface to a Win10 mini PC.

[mtrehy]

[mtrehy]

[mtrehy]

[mtrehy]

THanks,

How do I go about using the original spindle drive? I believe it was controlled by the computer and not sure what I need to do on the control board to mimic that...

[mtrehy]

[mtrehy]

[m_c]

That's the early system.

The spindle drive board (in your first picture post), should have everything marked on it.
As it's a NEControl, I'm not sure if a manual will be easily found, but some google searches might turn up something.

The only unknown will be what the inhibit (white/black wire) gets switched to. I'd trace that wire, and see if you can work out the circuit it connects to.
As it's connected to Inh (H), I suspect it'll get 5V applied to it to inhibit (disable) the drive, with 0V connected to the speed control L.

The grey and blue wires will go to a circuit that outputs 0-10V (or possibly 0-5V - you can measure the voltage between the L and H terminals, which will give you an idea) to set the spindle speed

Does the original computer power up?
If it does, it would be worth measuring the various voltages, as it'll help eliminate guess work.
It would also let you test the spindle drive, as SCR drives do have a habit of the SCRs failing causing the supply fuses to blow.

It's also worth measuring the voltages on the power supply board (Second photo).
If it's anything like the later board, it'll output ~24V for the stepper drivers, and 5V for the control, as well as providing a pass through for the spindle supply.

Although I'm not sure what the big plastic box does. Is that where the wires from the spindle drive board connect?
If so, it could the isolation circuit.