[declanhalpin]

Hi all,

I am building an auto-toolchanger for a Techno CNC machine, based on this design (but using a bed layout, instead of the "spider arm".

SO: I have a few newbie questions:

1 - at the moment, I have a relay panel setup to control the power that goes to the air solenoids. It's all wired up and works great, but I'm concerned that there is no "safety" built into the circuitry. The computer is connected directly to the relay board (mechanical relays, btw, not opto-isolated) and I'm worried a short circuit might send juice back through the LPT. Is this a valid concern? If so, how should I solve?

2 - I'd like to have a button on the spindle somewhere so I can release the tool into my hand instead of running an M6 command. I was thinking I could just wire the switch so it bypasses the relay - see attached image. Would this damage the relay?

thanks in advance!!

[Al_The_Man]

1/ make sure you have the commons connected together and earth ground point, your PC P.P. is already at earth ground most likely.
2/ As long as you do parallel to contacts and not the coil!!
Al.

[declanhalpin]

Hi Al,

Not sure what you mean re: parallel contacts. I was planning to split the 24vDC before it enters the relay, run it to the manual switch, then splice back in after the relay.

Are just recommending I don't use the physical relay as my "wire nuts"?

d

[Al_The_Man]

You show parallel connection across the relay, this cannot be across the coil otherwise you short the supply, if in parallel, it would be across the N.O. contacts?
I Never use wire nuts in a machine enclosure, and very rarely anywhere else come to that.
Al.

[declanhalpin]

Sorry Al, I'm a real novice at this stuff, so I'm afraid I don't follow. My plan is to totally bypass the relay as shown in my drawing. Will this short the relay?

d

[Al_The_Man]

On a relay you have 2 terminals for the coil, the other terminals are N.O. or N.C. contact, the number of which depends on the relay, If I read you right, you want to overide the contact action?
IOW, find out which N.O. contact pair is doing the switching and wire the N.O. switch in parallel.
Do NOT wire it across the coil terminals.
All of this is assuming this is a mechanical relay and not a solid state version, as this would change things altogether.
Al.

[declanhalpin]

Hi Al,

Ok, I realize my original drawing wasn't exactly accurate. In actuality the computer is driving the coil (it's a mechanical relay board). So, please take a look at the attached image and let me know if this is OK.

And thanks again for your help. These forums are priceless!

dh

[Al_The_Man]

That would be more like it.
Al.

[declanhalpin]

Sweet. Thanks!