Conect 121 CNC Lathe Project

[mtrehy]

I plugged the computer in and it immediately started popping and smoking! Suffice to say I think the BBC B is dead. I have a bit of time tomorrow so will power the control box and see what I can find.

I found this on another forum https://www.cnczone.com/forums/gener...78836-cnc.html

Seems to think I can attach a pot to 10, 11 & 12. Not sure what I have to do to the INH - assuming that is inhibit and INH (h) means that it is inhibit when pin 8 has 5v then presumably if it's disconnected then it should run - or maybe I am over simplifying!

[m_c]

You can connect a pot, which if you have one laying around (IIRC they're normally around 100k), I would wire up just to check the drive still works. But as I've already mentioned, be aware those control terminals are probably around half mains voltage.

However I'd aim to keep the spindle computer controlled.
Most breakout boards are capable of 0-10V control, and just need an isolated 12V power source to avoid issues with non-isolated drives. A small DCDC converter is typically used for this, but that power board may already provide an isolated supply.

Inhibits on those boards generally need connected to inhibit. In the case of H, it needs power applied, or in the case of L needs connected to 0V (which may not be 0V in relation to earth)

[mtrehy]

No luck yet with the motor controller. It has 240v to it, I can measure 12v across pins 12 & 10. I attached a pot to 12 & 10 and 11 and can vary 11 between 0-12v but not seeing any output from the motor controller. Tried it with inh connected and disconnected. The motor turns if I attach a 12v supply directly to it. Is there any more I can try with the original motor controller? There is also a component attached below the motor - not sure hat this is...?

[m_c]

That's a choke. They help smooth/suppress noise from the motor.
It's worth checking it's not failed and gone open circuit (either with a multi-meter, or apply the 12V with the choke in circuit).

Have you checked both fuses on the drive?
It could be the Inhibit needs a certain voltage applied, but without a manual, or being able to work out what the wire gets connected to and fed, it's pretty much guess work.

[mtrehy]

THanks MC.

How would that choke be wired? Is it in series like a resistor? It's not wired up at the moment.

[m_c]

It should be in series with the motor.
The fact it's been disconnected would indicate there's been a problem.

Depending on how much money you're willing to spend, and your modification abilities, if I was to retrofit one of these now, I'd probably fit a 750W servo motor and drive. Certainly more expensive than just a DC drive, but would give more control over the spindle (depending on which controller you fit).

[JohnHaine]

https://www.ebay.co.uk/itm/550W-Mute...edirect=mobile

[mtrehy]

That's interesting John. Have you used one?

[JohnHaine]

No but quite a few people over on the Model engineer forum have.

[mtrehy]

Not had much time but a bit of progress on this.

Replaced the original x axis stepper with a Nema23 which was a direct swap, bolt holes all the same etc.

I ordered a cheap chinese motor controller which arrived today and seems to work well - motor is dead quiet and smooth. It's running off a potentiometer so need to figure out how to get that controlled by software at some point.

https://www.ebay.co.uk/itm/282820954577

I have a fairly simple plan for attaching a Nema 23 to the Z axis so hopefully get that done next week.