Ohmic not sensing unless it is off torch

[whiskeymike]

I'm having issues with my ohmic sensor not sensing. I've replaced all of the consumables and still having an issue. Running a Bulltear table, CandCNC electronics DTHCIV ethercut

I take the ohmic wire off the retaining cap. touch it to the metal on the table and I get the yellow light in diagnostics.

I connect the ohmic wire to the retaining cap, with the consumables assembled to the torch and lower the torch to the metal touching it and I get no yellow light.

I take the consumables off the torch, with ohmic wire attached to the consumables without the torch, touch the metal and I get the yellow light.

It's like the torch is shorting out the ohmic sensor?

I tried different consumables, shields, swirl rings, electrodes, and nozzles.

Any ideas? I've noticed that my machine torch where the 4" piece attaches to the body of the torch seems to flex and turns more than I remember. Could something be loose inside?

[BTA Plasma]

Are you trying to use fine cut without a shield?

[whiskeymike]

No, I'm using the finecut shield. I think it's 220948.

[BTA Plasma]

That is the right one. Make sure the ohmic clip is actually touching the shield.

[whiskeymike]

I bent it down a bit to be sure it had contact, but no luck.

[ajfoxy]

I had a similar issue, but with a home built table. I worked it out that between the material, the slats and the water table I was not getting a complete circuit back to the ohmic sensor. I got round my issue by getting a wire with a crocodile clip both ends. I put the one end on the material I wanted to cut and the other end of the rail that the gantry runs along the y. Obviously put it at the end so it does not get run over. That seems to complete the circuit and enables to ohmic sensor to do its job. Not had any drama's since. Y.M.M.V.

[whiskeymike]

Thanks AJ. Did you have the same issue that it worked off the torch, but on the torch it was a problem? Mine has been working great for 6 months, but today decided to throw a tantrum.

[BTA Plasma]

The biggest thing is if it shows z home in the diagnostics tab. Check the plugs on the module itself

[Thor]

Is the shield tip clean? I have had a few times when it just had a coating of slag dust on it that it seemed to not work. Quick wipe with some soft steel wool and back to good.

[jimcolt]

The wire must make a connection to the shield......check continuity with the torch assembled from the shield to the clip where the wire attaches. Often the shield is dirty or the tab that has to touch the shield is not making good contact (bend it so it does!). if you touch the ohmic wire to the plate and it senses the plate.......yet it does not work through the shield.....then it has to be the connections from retaining cap to shield to plate. Clean the plate side of the shield periodically with scotchbrite as well. No rocket science on these connections!

Jim Colt Hypertherm

[tcaudle]

Its basically a continuity tester. One side goes to the Shield and the other goes to the material. If you can touch the two inputs on the FT-01 named TIP and PLATE together and you get the yellow SENSE light then has to be in the connections. The Plate side uses the table structure as the "wire" for that side The TIP terminal uses the Shield . If you can get it to light by directly touching the plate with the TIP wire then the only thing left is the connection at the shield.

If you want to understand how it works get a meter with a continuity test option (beeps when the black wire is touched to the red) and put one wire (black) down on the plate and touch the other to the PLATE input on the FT-01. If you don't get a beep the circuit is open. Start moving on the gantry with RED wire while keeping the black tied to the actual metal on the table, the move the RED down to the table structure unit you do get a beep. That will confirm that the PLATE side of the circuit is working.

[Largemouthlou]

Not sure why yours wont work with torch installed, makes about as much sense as mine not working periodically. Not blaming the unit, I believe it is the material. I can move it all over the sheet to ck and it will sense, but go back to bad spot and it won't.

Been a while since I have had my problem, everyone was good about trying to help. I basically ran another wire to where I run the table from, if it don't sense then I stop the code raise the torch and restart the code, when the torch comes down to sense I then touch the extra wire I ran from the shield to the steel v rail and it makes the connection and keeps on going.

[whiskeymike]

Yep, doesn't seem complex. But it seemed very odd that the wire directly worked. Then unscrewing the consumables from the torch, with the ohmic wire attached, touching the shield to the plate works. But then screwing the consumables back on to the torch, and grabbing the torch off the magnetic mount, touch the plate and I couldn't get it to light up, was very odd. Wasn't sure if something in the torch could be messing up the continuity.

I was pretty frustrated/tired after replacing all of the consumables and screwing around with it. So I'll try it again tomorrow night with a clear head. It'll probably work out of the gate. . Thanks guys

Is the bottom 4 inches of the torch, just above the consumables loose for you guys? I can twist mine about 90 degrees

[tnbndr]

and grabbing the torch off the magnetic mount, touch the plate and I couldn't get it to light up

Keep the torch attached to the gantry and lower it manually to the plate and it should work, complete the circuit.

[whiskeymike]

and grabbing the torch off the magnetic mount, touch the plate and I couldn't get it to light up

Keep the torch attached to the gantry and lower it manually to the plate and it should work, complete the circuit.

Yep, I neglected to mention it since I figured it was obvious. It all started when the torch would lower, make contact and keep driving into the plate because the circuit wasn't made. My point of taking the torch down off the gantry was that I was able to run the shield into the plate from many angles with no circuit being made. I was also able to touch the plate in a 10" area around the torch to minimize it being the plate covered in rust, too much mill scale, etc.. In addition to the scenarios I listed, I lowered the Z and no circuit was made.

I'll see about cleaning everything up again and try it out tonight. Thanks for the help.

[BTA Plasma]

The orange light doesn't mean anything unless the Z home comes in in the diagnostics tab. That is where home circuit completes for a program. If it doesn't you cannot REF nor run any program. Youll need to start there.

[whiskeymike]

Not sure what you mean. I'm referencing the yellow light in the diagnostics tab in Mach 3 on the computer screen.

[BTA Plasma]

Orange light on the Feather touch, yellow in Mach. However due to the latency you cannot touch off faster than 25-28ipm. So what is your velocity set to in Mach? And what is the Z home speed percentage set to in homing/limits Z home.

Also if you received an OHMIC retaining clip like this you can pretty much blame the clip. This clips lower tab had to be bent to work by the local MFG that has a Star-Lab machine.
The clip was clipped on with a mis clocking from the retaining notch when it was mfg. Make sure your clip is good. Also make sure your speed is not too fast. Zero about 1 inch above the plate and let it come down slow to test.

[whiskeymike]

I see. I'm not sure the speed as I'm at work, but it's been working for 6 months and just started this. For testing, I just jog the Z down manually and leave the torch still and the light didn't come on. I replaced the retaining cap and also tried to bend down the clip to make sure it was touching a new shield.

I'll try it tonight and report what happens.

[poppopsworkshop]

I've had the same issue Whiskeymike only while I used the fine cut consumables. What I found is the I could take a metal wire or screwdriver and touch between the cap and the metal being cut. It would sense then. otherwise it would not sense. I started to grind my metal "shinney clean" and it now works 1/2 the time. I went back to the standard consumables and havent had a issue since then. Hope this helps.

[jimcolt]

I have no issues with the Finecut (or the regular shielded consumables) with the ohmic unless the material has paint, primer or heavy rust on it. With the paint and primer you must remove them.....I find when there is rust you can often (using a pump spray bottle) spray on a light coat of water.....which makes the surface conductive for the ohmic contact process.

Jim Colt Hypertherm

[whiskeymike]

So I've made some progress, but still puzzled.

I took the continuity comment to heart and tested the wire running from oohmic sensor box from CandCnC through the wire/hose cage to the torch. Sometimes continuity, sometimes not. So figured it was the wire was broken. Ran another one, continuity was intermittent.

Finally figured out that that if the main big box from CandCnC is turned on, I lose continuity. Turn it off, get continuity back. Specifically it's when I put it online and it locks the steppers. I tried moving my new wire away from the stepper wires, but no change.

Is it possible the stepper wires are putting off RF that is stopping the continuity? Or what the heck is going on?

I'm baffled.

I hooked up the wire from the box to the torch without going through the wire cage and gantry, but that's not a solution.