Intermittent flashing of #1 input light - Que?

[johnm]

Folks -

We were building some bat houses for a kid's woodworking class I'll be teaching on Sunday, and I noticed that the #1 input light would flash intermittently. No real rhyme or reason - it didn't occur during a specific gantry move, or Z move... The machine didn't crash or anything, but it was surely flickering.

Any ideas?

John Moorhead

[mikejohn]

It sounds as though your z plate or wire is touching the shopbot.

..............Mike

[gerald_d]

Hole in the holster?

[johnm]

Folks -

Okay, I've discovered the problem... I have a medical condition that I've suspected was becoming chronic, but this is more of a confirmation that I need.... attention...

My name is John, and I suffer from Cranio-Rectal Inversion.

D'oh! I had set Z zero and not removed the grounding clip from the spindle ground lug...

If all my problems were this simple...

John

[gerald_d]

If I am reading this correctly, you have a perfect illustration of why good grounding is required.....

You have a ground wire (not an input wire) clipped to a ground point and yet you get input signals.

[johnm]

Gerald -

Are you saying I have an open ground? I was in radio (engineering) for longer than I'll admit and am fastidious about grounds - I've chased too many "ghosts in the machine" that were attributable to ground faults or interferences...

I have a grounding lug on the spindle, one on the Z gantry, one on the Y gantry, 2 on X, two on the metal table, 1 in the control box, one on the drive computer and they are all hooked together with 2 #12 ground wires running to a 6'+ long grounding rod.

Now, since I've removed the clip and returned everything to the "holster" I haven't had a trouble.

At rest I show ZERO ohms resistance from the body of the spindle to the ground lug on the table. How would you suggest I check for a voltage drop during operation?

Let me know what you think...

Thanks!

John

[gerald_d]

John, those years in radio engineering make you much more qualified to tell us what is happening there! I am as mystified as the rest on the grounding of a ShopBot. And we have the same experience that loose ground connections cause inputs - there is one particular ground connection in our SB that has to be tight otherwise the z-axis starts moving. My only conclusion is that the SB control system is far too susceptible to the tiniest of signals.

Or, have you perhaps wired the clip and the plate the wrong way around?

[gus]

Input 1 (on Alpha) is in a high state (about 5 VDC) when not active. When active this input is pulled low (0 VDC or something less than 5 VDC) and sets the input. So all things being normal if you are running and the light on input 1 is flashing that would say that the input is being pulled low. Maybe the lead to the z-zero plate or the plate itself is being shorted to your well grounded machine. Unhook the z-zero plate at the control box and see it it still does it. Or hook up your Digital Storage Scope to the input and see what it going on on the input with the machine working.

[paco]

My router motor is always grounded and I clip my Z-plate on the carriage with a metal clip. It's flashing and not a problem. It could be if the control was looking for an #1 input (ON INP(1,1) something to do) but the fact is that in normal cutting file, it's not looking for an input from the #1.

Might be intersting to know that it is looking for input on the #3 (limit switches) pretty much all the time... unless you didn't set input #3 as limit system.